Category Archives: AC & Thermal Management

Replacing Thermostats Along with Water Pumps

Gates explains why it makes sense to replace thermostats along with the water pump. 


It is good garage practice to change the water pump as part of a scheduled drive system maintenance programme. This makes sense whether the water pump is driven by the timing belt or the accessory belt. In most workshops, however, thermostats are not normally replaced as part of either a scheduled timing belt maintenance programme or an accessory belt replacement.

“If the thermostat fails and the timing belt has to be removed before it is possible to gain access to it, changing the timing belt at the same time as the thermostat becomes the most appropriate solution.”

After removing a water pump, the cooling system should always be flushed to expel all potential contaminants, whether chemical or physical debris. Failure to flush the cooling system could lead to premature water pump failure. As the thermostat would prevent the whole of the system being flushed, it should be removed. It is good garage practice to fit a new thermostat and gasket after the system has been flushed, rather than risk refitting the old ones.

Common engine designs

The location of the thermostat can also be a critical issue. For example, in certain VW Group models fitted with V6 engines, the thermostat is seated directly behind the timing belt drive. Typical applications include Audi A4, A6 and A8. The Vauxhall Astra, Corsa and Meriva 1.6 petrol four cylinder engines have a similar design. In both the VW and the Vauxhall/Opel examples quoted, the timing belt must be removed before the thermostat can be replaced.

If the thermostat fails and the timing belt has to be removed before it is possible to gain access to it, changing the timing belt at the same time as the thermostat becomes the most appropriate solution. Re-installing components from the previous layout risks premature drive system failure, warns Gates.

This is because the ‘installation tension’ of the timing belt is a critical measurement that cannot be reproduced. As new belts are never reliable partners for older tensioners and idlers, new belts should always be fitted alongside new tensioners and idlers.

Timing belt kit solution

After considering the problems associated with parts identification and system compatibility, Gates devised a simple solution that benefits both installers and their local motor factor. The Gates PowerGrip Kit Plus Water Pump Plus Thermostat range means that it is possible to order all of the matching parts and to receive them in a single box, all at the same time. It should be noted that such kits for Subaru Impreza, Forester and Legacy also include a Gates spacer tool that resolves other fitting issues that had previously caused premature drive system failures on these models.

Each of these is an example of a practical and cost-effective solution for installers, with an emphasis on improving workshop efficiency and increasing installer protection. This is because there is a Gates part number for each of the vehicles mentioned so far and because all of the parts inside the box are covered by the same Gates warranty.Screen Shot 2017-07-03 at 11.04.39

Why thermostats fail

Thermostat failure is usually mileage and age- related. Most drivers only become aware of a problem when the cabin heater doesn’t work as well and, unsurprisingly, that’s during the colder winter months. A thermostat sticks shut if the wax element is damaged by

previous overheating, corrosion or age. It blocks the circulation of coolant in the engine. It’s this that causes the radiator to overheat, which could be disastrous.

‘Fail-safe’ thermostats fail in the ‘open’ position and cause the engine to overcool. This creates problems such as a slow warm-up cycle, poor heater performance in the cabin, increased engine emissions and reduced fuel economy.

The effects of an ‘open’ failure are undesirable, however they are far less catastrophic than those of a ‘closed’ failure.

Hot tips for colder engines

Gates says it makes planning for the replacement season easier by recording the fastest selling thermostats around Europe. The 2016 results are in. Check out the table below, which also includes some new-to-range items:

Screen Shot 2017-07-03 at 11.05.23

In many cases, it makes more sense to replace thermostats while the timing belt is stripped down and in these cases, the Gates PowerGrip Kit Plus Water Pump Plus Thermostat range makes things easier. All components match OE specifications, are ideal for each application and all fall under the same Gates warranty.

Visco clutch

General points

The Visco clutch is part of the Visco fan. If has the task of creating the frictional connection between the drive and the fan wheel depending on temperature, and thus influencing its speed. There is a plastic fan attached to the clutch which generates the air flow as required.

Visco fans are mainly used in cars with longitudinally- mounted large-capacity engines and in trucks.

Design/Function

Screen Shot 2017-06-09 at 15.55.24

The Visco clutch is usually driven directly by the engine via a shaft (Fig. 1). If no cooling air is required, the Visco clutch switches off and continues to run at a lower speed. As requirements increase, silicone oil flows from the storage area into the working area. There, the drive torque is transferred to the fan, the continuously variable speed of which is set automatically on the basis of the operating conditions by means of wear-free viscous friction. The switching point is around 80 °C. In the case of conventional Visco clutches, the air expelled by the fan meets bi-metal (Fig. 2), the thermal deformation of which has the effect of opening and closing a valve via a pin and valve lever. Depending on the valve position and thus the amount of oil in the working area, the transferred torques and fan speeds are set. The amount of oil required is 30 – 50 ml (passenger car). Even with the working area completely full there is a difference between the speed of the drive and that of the fan (slip). The heat produced is dissipated to the surrounding air via the cooling ribs.

Screen Shot 2017-06-09 at 15.55.34

In the case of the electrically triggered Visco clutch, control takes place directly via sensors. A regulator processes the values and a pulsed control current carries these to the integrated electromagnet. The defined guided magnetic field regulates the valve which controls the internal oil flow via an armature. An additional sensor for fan speed completes the regulator circuit.

Electronically-controlled Visco clutch:

Screen Shot 2017-06-09 at 15.58.03

Effects of failure

A faulty Visco clutch can become noticeable as follows:

  • Increased engine temperature or coolant temperature
  • Heavy noise development
  • Fan wheel continues to run at full speed under all operating conditions

The following can be considered as possible causes:

  • Lack of frictional connection through leaking oil
  • Loss of oil due to leak
  • Soiling of the cooling area or bi-metal
  • Internal damage (e.g. control valve)
  • Bearing damage
  • Damaged fan wheel
  • Permanent full frictional connection due to faulty clutch

Troubleshooting

Screen Shot 2017-06-09 at 16.00.32

Test steps towards recognising faults:

  • Check the level of coolant and the antifreeze content
  • Check the Visco clutch with regard to outer soiling and damage
  • Check the bearing for play and noises
  • Make sure no oil is leaking
  • Check the Visco clutch by turning it by hand with the engine switched off. With the engine cold, the fan wheel should be easy to turn and with the engine hot it should be hard to turn.
  • If possible check the slip of the clutch using speed comparison between the speeds of the fan and the drive shaft. With full frictional connection, the difference may only be max. 5% for directly driven fans. An optical speed measuring device with reflective strips is suitable for this purpose (Fig. 3)
  • Check the electrical connection (electronically- triggered Visco clutch)
  • Check air cover/air baffle plates
  • Make sure there is enough air flowing through the fan

Expansion tank

General points

The expansion tank in the cooling system is usually made of plastic and is used to trap the expanding coolant. It is normally installed in such a way that it represents the highest point in the cooling system. It is transparent to allow the coolant level to be checked, and has “min” and “max” markings. In addition, an electronic level sensor can be installed. Pressure compensation in the cooling system is achieved by means of the valve in the lid of the expansion tank.

Screen Shot 2017-06-09 at 15.40.11

Design/Function

An increase in coolant temperature leads to an increase in pressure in the cooling system since the coolant then expands. This increases the pressure in the expansion tank, opening the pressure control valve in the lid and allowing air to escape.

When the coolant temperature is normalised, a vacuum is created in the cooling system. Coolant is sucked back out of the bottle. This in turn creates a vacuum in the bottle. As a result, the vacuum compensation valve in the lid of the expansion tank is opened. Air flows into the bottle until the pressure has been balanced.

Screen Shot 2017-06-09 at 15.40.45

Effects of failure

A faulty expansion tank or a faulty lid can be noticed as follows:

  • Loss of coolant (leak) at various system components or the expansion tank itself
  • Increased coolant and/or engine temperature
  • Expansion tank or other system components are cracked/burst

The following can be considered as possible causes:

  • Excess pressure in the cooling system on account of a faulty valve in the lid
  • Material fatigue

Troubleshooting

Test steps towards recognising faults:

  • Check the level of coolant and the antifreeze content
  • Check whether the coolant is dyed/soiled (oil, sealant, lime deposits)
  • Check thermostat, radiator, heat exchanger, hose lines and connections for leaks and function
  • Burst test the cooling system if necessary (pressure test)
  • Make sure no air is trapped in the cooling system, vent the system according to vehicle manufacturer’s instructions if necessary

If all the above points are carried out without complaint, the lid on the expansion tank should be replaced. It is very difficult to test the valve on the expansion tank lid.

Heat Exchanger

General points

The heat exchanger is installed in the heating box of the vehicle interior and has coolant flowing through it. The interior air is routed through the heat exchanger and thus heated up.Screen Shot 2017-06-09 at 15.08.21

Structure/function

Like the coolant radiator, the heat exchanger is made up of a mechanically jointed pipe/fin system. The trend is moving to all-aluminium design here, too. Coolant flows through the heat exchanger. The flow quantity is usually controlled by mechanically or electrically controlled valves. The interior air is heated up via the cooling fins (network) of the heat exchanger. The air flow produced by the interior fan or the wind blast is routed through the heat exchanger which has hot coolant flowing through it. This heats up the air which is returned to the inside of the vehicle.

Screen Shot 2017-06-09 at 15.09.22

Effects of failure

A faulty or poorly working heat exchanger can become noticeable as follows:

  • Poor heating performance
  • Loss of coolant
  • Odour build-up (sickly-sweet)
  • Fogged windows
  • Poor air flow

The following can be considered as possible causes:

  • Poor heat exchange caused by external or internal impurities (corrosion, coolant additives, dirt, limescale deposits)
  • Loss of coolant through corrosion
  • Loss of coolant through leaky connections
  • Soiled interior filter
  • Impurity/blockage in the ventilation system (leaves)
  • Faulty flap control

Troubleshooting

Test steps towards recognising faults:

  • Watch out for smells and windows fogging
  • Check interior filter
  • Check heat exchanger for leaks (hose connections,beading, network)
  • Watch out for impurities in/discolouring of the coolant
  • Check coolant flow (blockage through foreign matter,limescale deposits, corrosion)
  • Measure coolant inlet and outlet temperature
  • Watch for blockages/foreign matter in the ventilationsystem
  • Check flap control (recirculated air/fresh air)

Causes of noise

Hints for fault diagnosis of noises and compressor exchange

The following notes should be observed for fault diagnosis (noise sources) and before every compressor exchange:

  • Check all the retaining bails and mounting points for cracks, missing bolts or nuts. Any vibration can cause excessive compressor noise. Lever gently against the brackets and mounting points with a tyre lever for example, to see if the noise changes pitch. If it does, the noise is not caused by the compressor.

Screen Shot 2017-06-05 at 15.33.08

  • Check the hoses to see if they are transferring the engine vibration back to the passenger compartment, causing the noise. Grip the hoses tightly in your hand to see if the noise changes.Screen Shot 2017-06-05 at 15.41.48
  • Check all drive belts, idlers, pulleys and tensioners for exessive movement, ease of rotation and alignment. The extra movement can be caused by worn parts, which create the excessive noise.
  • Excessive high pressure can cause abnormal compressor noise. If the high pressure service port is located after a blockage, the real pressure can be much greater as shown on the gauge. Checking the temperature of the condenser will help diagnose the problem.Screen Shot 2017-06-05 at 15.42.17
  • An overcharge of refrigerant, or charging with contaminated refrigerant will cause excessivley high pressure, causing compressor noises. Refrigerant that contains excessive levels of non-condensable gases (air) will also cause noise.
  • Insufficient airflow across the condenser will cause excessive high pressure, which might cause compressor noise. If air is inadequately fed to the condenser, the refrigerant cannot condense sufficiently and the high pressure rises excessively. This can cause abnormal noises. Be sure that the fan/fans are transporting enough air to the condenser. Check also the condenser and radiator fins for any fouling.Screen Shot 2017-06-05 at 15.42.45
  • Often noises can be caused by dirty expansion valves or orifice tubes often. This can arise from pollutants in the form of, e.g. metal particles. Through this, the refrigerant flow is reduced and this leads to an increase of the high pressure. Faulty expansion valves can produce various clatter-, whistle- or roaring noises for example. These can be also readily noticed inside the car.

Screen Shot 2017-06-05 at 15.43.39

Are BHS compressors filled with oil on delivery?

Screen Shot 2017-06-05 at 15.03.27No matter the delivery state of the compressors, the oil filling level and viscosity must be checked for every compressor before installation in the vehicle, and corrected according to the manufacturer’s specification and enclosed documentation if necessary.

The reason is that many compressors can not only be used in one vehicle, they can be used in a wide range of different vehicles. The respective oil quantity must be adapted accordingly.

The individual steps are clearly presented in this description.

Since most compressors do not have an oil draining screw, oil can only be removed through the high and low-pressure fitting or through the filling bore hole in these cases.

 

 

 

1.Pour the filled oil into a receptacleScreen Shot 2017-06-05 at 15.04.28

Turn the drive shaft to make sure that all the oil is removed.

 

e.g. with filling bore hole

 

 

 

 

 

e.g. without filling bore hole through the high-pressure connection

 

 

 

 

 

 

2.Measure the drained oil quantity

Screen Shot 2017-06-05 at 15.05.22

3.Determine the oil quantity to be filled into the compressor

If the complete oil quantity has been removed from the system for the the air-conditioning system to be flushed, the complete oil quantity must be filled into the compressor again. The quantity specifications can be found in the Hella online catalogue in the filling quantity handbook (following login to the Hella Aftermarket Club) or with the aid of respective specialist literature.

4.Fill the prescribed quantity into the compressor

Screen Shot 2017-06-05 at 15.06.01The complete prescribed quantity is filled into the compressor. If the device has not filling bore hole, then through the low-pressure connection. Turn the drive shaft at the same time. The complete system quantity might not be able to filled into the compressor. In these cases, feed the residual quantity through the service unit.

e.g. with filling bore hole

 

 

 

 

 

e.g. without filling bore hole through the low-pressure connection

 

 

 

 

Flushing

Flushing the air conditioning system and its components

Air conditioning systems are flushed to remove soiling and damaging substances from the refrigerant cycle. The following information is intended to support users in their introduction to the subject of “flushing air conditioning systems” by providing answers to important points such as:

  • Why air conditioning systems have to be flushed at all
  • What the term “flushing” means in the context of vehicle air conditioning
  • What types of soiling can be removed by “flushing” and/or what effects these types of soiling have
  • Which flushing methods are available and how they are used.

Why should a vehicle air conditioning system be flushed at all?Screen Shot 2017-06-05 at 14.02.30

Faulty system components (old filter-dryers (photo), compressor damage etc.) can lead to dirt particles picked up by the refrigerant being distributed in the whole air conditioning system. If in the case of compressor damage, for example, only the compressor is replaced, dirt particles can collect in the new compressor within a very short time and lead to the destruction of the newly installed system components as well as the expansion valve/throttle valve or multi-flow components – expensive follow-on repairs are the logical consequence. To avoid this, the system must always be flushed following component damage which could lead to soiling of the refrigerant cycle through metal chips, rubber abrasion etc.! Many vehicle or compressor manufacturers (e.g. Ford + GM / Sanden + Visteon) already require that systems are flushed.

What does the term “flushing” mean in the context of vehicle air conditioning?

The term “flushing” is used to describe the removal of soiling or damaging substances from the refrigerant cycle. Flushing is necessary to enable professional repairs to be carried out, avoid expensive follow-on repairs, maintain warranty claims towards suppliers and ensure customer satisfaction.

What types of soiling can be removed by “flushing” and/or what effects do these types of soiling have?

  • Screen Shot 2017-06-05 at 14.03.07Abrasion in the case of compressor damage:
    The material particles block expansion valves, throttle valves (orifice tubes) or multi-flow components (condensers, evaporators)
  • Humidity:
    Expansion valves and orifice tubes can freeze up. Chemical reactions between refrigerants and refrigerant lubricants on the one hand and humidity on the other can form acids which make hoses and O- rings porous. System components are damaged by corrosion.
  • Elastomers (rubber):
    Elastomer particles block up expansion valves, orifice tubes or multi-flow components.
  • Screen Shot 2017-06-05 at 14.03.53Soiled refrigerant lubricant or refrigerant:
    Soiled refrigerant or the mixing of different refrigerant lubricants can also lead to acid formation. These acids can make hoses and O-rings porous. Further system components can also be damaged by corrosion.

Which flushing methods are available and how are they used?

1. Nitrogen 2. Chemical agents 3. Refrigerant

1.) Nitrogen:

The connection pipes or system components have to be flushed individually. With the aid of a universal adapter they are blown out and dried using pressurised nitrogen (max. 12 bar). For this purpose a cone-shaped adapter connected via a hose and a pressure reducer to the nitrogen bottle is connected alternately to the ends of the hose or the components to be flushed.

Advantage:
The only costs incurred are the low costs for the medium itself, no disposal costs.

Disadvantage:
Additional labour costs are incurred for fitting and removing the hoses and system components. A cleaning effect is not achieved when nitrogen is used for flushing. In addition, nitrogen is not suitable for loosening jammed particles. Nitrogen can only be used to blow out loose dirt particles and for drying purposes.

Screen Shot 2017-06-05 at 14.04.332.) Chemical agent (flushing fluid):

The connection pipes or system components have to be flushed individually. They are flushed by means of a chemical agent (flushing fluid) with the aid of a universal adapter on a flushing gun. Following the flushing process, nitrogen must be used to remove the residual flushing agent from the refrigerant cycle and the refrigerant cycle has to be dried.

Recommendation:
Maximum effectiveness is achieved by combining the use of flushing fluid and nitrogen. Initially, flushing with flushing fluid loosens even jammed particles and hardened deposits. The subsequent blow-out with nitrogen completely dries the refrigerant cycle or components again.

Disadvantage:
Costs for the chemical cleaning agent and its correct disposal as well as additional labour costs for fitting and removing the pipes and components.

3.) Refrigerant:

During flushing with the refrigerant (R134a) the existing air conditioning service station is equipped with adapters and filter elements to flush liquid refrigerant through the refrigerant cycle.

Screen Shot 2017-06-05 at 14.08.19Disadvantage:
Only loose dirt particles and oil can be removed from the system. In addition, adaptation plates are required to be able to flush correctly. These adaptation plates cause increased costs on account of additional installation and removal work. The service station is not available for other vehicles during the application.

Note:

Whereas tube & fin and serpentine components can usually be cleaned easily, it is often not possible to clean components which use multi-flow (parallel flow) technology. If there are doubts about the success of cleaning such components, the component must be replaced.

Following refrigerant cycle flushing, care must be taken that a sufficient amount of new oil is refilled into the system. The following specifications (% of total oil quantity) serve as a guideline:

Condenser: 10%

Dryer/accumulator: 10%

Evaporator: 20%

Hoses/pipes: 10%

Flushing set 100 (part no.: 8PE 351 310-001) has been designed for flushing with flushing fluid and is made up of the following components:

  • Gun with plastic cone-shaped connector (resistant to oil and acids)
  • A spiral hose that can be extended to 2 m for connection to the supply bottle
  • Screen Shot 2017-06-05 at 14.05.44  Supply bottle (1 litre, operating pressure 4.5 to 6.5 bar with suspension fixture and pressure relief valve (24 bar), quick-action connection with manometer marked with both bar and psi and a ventilation valve
  • Wall bracket with dowels and screws
  • Plastic tank (5 litres) for collecting used flushing fluid
  • Cover for plastic tank with 2.5 m of transparent hose and connection cone
  • 2 attachment brackets for connection cone
  • Operating manual in 5 languages (English, German,French, Spanish and Italian)

A 1⁄4″ adapter with a right-hand thread is required for the supply of compressed air to the air conditioning Screen Shot 2017-06-05 at 14.10.55system flushing set 100. Since different hose and adapter systems are used in different European countries, this adapter is not included in the scope of supply.

Behr Hella Service supplies the following flushing fluid for the flushing process:Part no. 8FX 351 310-081: (1,000 ml)

Part no. 8FX 351 310-071: (3,785 ml)

Flushing set 150 (part no.: 8PE 351 310-111) has been designed for flushing and drying with nitrogen and is made up of the following components:

  • Nitrogen pressure reducer
  • Universal flushing adapter with connection cone
  • Screen Shot 2017-06-05 at 14.12.23Hose (1.8 m)In addition, Behr Hella Service also supplies a bottle cart (8PE 351 226-011) for the safe transport and storage of 10 l nitrogen bottles.

When the adapter 8PE 351 216-111 and the filling adapter 8PE 351 216-001 (high-pressure side) or 8PE 351 216-011 (low-pressure side) are used, flushing set 150 can also be used directly for pressure testing at the vehicle. In this case 12 bar should not be exceeded.
General notes on flushing:

  • Please read the respective operating manuals, instruction leaflets, instructions from vehicle manufacturers, safety data sheets etc. through carefully
  • Screen Shot 2017-06-05 at 14.12.54Before and during flushing, make sure you heed the respective safety conditions including the technical information sheets “Handling refrigerants” and “Removal and fitting instructions”.
  • Compressors, dryers/accumulators and expansion valves and orifice tubes cannot be flushed.
  • Make sure that all dirt particles or damaged components have been removed from the refrigerant cycle.
  • Make sure there is no residual flushing solution in the system by drying the components thoroughly using nitrogen (do not use compressed air).
  • Fill the compressor with the correct amount/specification of oil (PAO-Oil 68 is particularly suitable) Take the quantities for the flushed components into account here.
  • Rotate the compressor 10 times by hand before putting it back into operation.
  • After installing the compressor, start up the engine and then operate the air conditioning at idling speed for a few minutes.
  • Replace the filter-dryer or accumulator and the expansion valve or orifice tube.
  • Fill the refrigerant cycle with the prescribed amount of
    refrigerant once it has been evacuated according to specifications.
  • Only R134a may be used as a refrigerant.
  • Carry out a system pressure, functional and leak test.

Screen Shot 2017-06-05 at 14.13.16If the above-mentioned points are not heeded, the respective warranty is no longer applicable.

Fault diagnosis

Cooling performance check

Every workshop needs, besides special tools, technical knowledge to do a proffesional job. This can be purchased by special training. This applies particularly to air-conditioning systems. The following instructions can merely serve as guide due to the different systems in use.

Screen Shot 2017-05-18 at 16.41.55

It is very important to correctly interpret the pressure gauge reading. Some typical examples:

Screen Shot 2017-05-18 at 16.42.32

Ambient temp= surrounding environment temperature.
Tests should not be carried out in extreme cold or warm environmental conditions.

Compressors without magnetic clutches

General

Screen Shot 2017-05-18 at 15.27.04For some years, so-called clutchless, externally triggered, variable compressors have been used (Fig. 1). All well-known compressor manufacturers use a great variety of different basic types. Here is a list of the most common types on the market: Denso, with the types 6SEU & 7SEU, Sanden, with the types PXE 13 & PXE 16. However, Delphi/Harrison is also represented via the CVC7 series, the design of which is very similar to the V5 compressor. This generation of compressors is used by almost all vehicle manufacturers (Audi, BMW, Citroen, Seat, VW, Opel). Externally triggered means that the stroke volume of the compressor is determined by a built-in control valve that is triggered by the air-conditioning control unit, depending on a wide variety of system parameters such as outside/desired temperature, high/low pressure, rotational speed, engine load. Clutchless means that the compressor no longer has an electromagnetic clutch. This means that the compressor is permanently driven via the pulley and works even if the air-conditioning system is switched off. However, in relation to this, the power is regulated down to a few percent.

Screen Shot 2017-05-18 at 15.28.06Operation

The pulley unit of the compressor consists, for example, of a drive plate and the actual pulley (drawing). The drive plate consists of a rubber element and forms the connection between the pulley and the compressor shaft. It acts as a vibration damper and also protects the compressor or the other driven units from overload or damage. If the compressor should lock up for example, the transmission forces between the pulley and the drive plate increase considerably in the area of the rubber element.

Depending on compressor manufacturer or type, the connection is interrupted by the deformation of the rubber element or by the triggering of an overload protection . The pulley then simply runs freely. This prevents damage to the belt or other units driven by the belt.Screen Shot 2017-05-18 at 15.36.42

The control valve (Fig. 2) is located in the compressor and receives its pulse-width modulated signals (PWM) from the air-conditioning control unit. The current which is fed from the control unit to the control valve, and which ultimately determines the power of the compressor, can be displayed as a measured-value block with the aid of diagnosis equipment. Clutchless compressors also have a safety valve (Fig. 3), which is intended to protect the compressor and the other
components of the air-conditioning system from excessive pressure. The valve usually triggers at a pressure between 35 and 45 bar (depending on the compressor manufacturer). The valve opens only until the overpressure has reduced. Afterwards, it closes again, so as not to release the entire quantity of refrigerant into the atmosphere. If the film of the valve is damaged, it can be assumed that the valve has triggeredScreen Shot 2017-05-18 at 15.37.23

Diagnosis

The pulleys and their rubber elements that are designed as overload protection are,
depending on the compressor type, designed differently. Depending on the type, it is possible in different ways to determine whether or not the overload protection has
been triggered:

  • Rubber abrasion parts are visible on the inside of the pulley (Fig. 4). The compressor shaft is no longer driven. Provided that the compressor can be turned easily, the pulley and the rubber element can be replaced.Screen Shot 2017-05-18 at 15.39.23
  • The over load protection has triggered the drive plate (Fig. 5). The drive plate and the rubber element can be replaced individually.
    Prerequisite: The compressor can be turned easily.Screen Shot 2017-05-18 at 15.39.58
  • A triggered torque limiter cannot necessarily be detected visually. In order to check whether the limiter has triggered, the compressor shaft must be held using a suitable tool (Fig. 6), and, at the same time, the pulley must be turned to the left. If the pulley can be turned to the left, the limiter has triggered and the compressor must be replaced. In the case of compressor types Sanden PXE 13 and PXE 16, replacement of the torque limiter is not possible.

Screen Shot 2017-05-18 at 15.45.22
In the case of the Audi A3 for example, at the lowest temperature setting, the maximum current that is fed from the control unit to the control valve is approximately 0.65 A. In relation to this, the compressor reaches its maximum power. In regulating operation, an average current of 0.3 A flows. In the case of newer vehicles, however, the problem is that diagnosis outside the engine-management area is not yet possible with many testers. Here, ideally, the use of an oscilloscope is helpful. With the aid of suitable test peaks, the PWM signal at the plug connection of the compressor can be recorded. In relation to this, the oscilloscope should be set to 5 V/div and 0.5 ms/div. With the engine running, the individual modes of operation can now be depicted on the screen of the oscilloscope. In the case of the lowest temperature setting ( Lo ) a square wave signal with a duty factor of approximately  75% (Fig. 7) is shown. The duty factor results from the ratio of pulse width -B- and the signal distance -C- (in this case 75% operating time, 25% switch-off time). At the same time, a readout of the level of the vehicle-electric-system voltage (approximately 13.5 V) can be taken on the basis of the volt divisions (A=5 V). The voltage value(9.8 V) displayed as a number is simply an average value. The pulse width depends on the desired cooling performance and the vehicle-electric-system voltage. Over the distance of the area -B-, the current to the control valve from the control unit is regulated . Depending on the setting of the control panel and ambient influences (e.g. outside temperature) the pulse width of the square wave signal is changed in such a way, or the control valve is triggered in such a way, that the compressor power necessary to reach the desired temperature is produced. Fig. 8 shows how, in the case of the temperature setting High, the compressor is regulated downwards. Fig. 9 was recorded in Econ operation (compressor off) and shows no signal. On the basis of these methods, it can be determined to what extent asignal change takes places through the control unit. If a plausible change of the signals takes place, but no change in the blow temperature or lowering of the interior temperature results, the compressor is probably faulty.Screen Shot 2017-05-18 at 15.45.52

Screen Shot 2017-05-18 at 15.46.34
In addition, there is diagnosis equipment on the market with which it is possible to generate a PWM signal with a different pulse duration. Thus, it is possible to determine whether a triggering of the compressor leads to a change in the refrigerant pressure. This serves as the basis for being able to make a statement as to what extent the compressor still functions perfectly.Screen Shot 2017-05-18 at 15.47.30

A functional check by means of a PWM signal can also be carried out using a function generator (Fig. 10). For this, it is however essential to connect a load which corresponds to that of an electronic control valve to the control-unit side of the air-conditioning system. Otherwise, the control unit will detect a fault in the system and will store this in the fault memory. This can lead to malfunctions or to failure of the system. In this case, a readout of the fault memory must be taken and
deleted using diagnosis equipment.

Screen Shot 2017-05-18 at 15.47.51
Again and again, complaints about compressors are hastily filed in connection with noises and other problems of air- conditioning systems. In very many cases, it turns out that the compressor  is alright, or that the cause of the fault does not stem from the compressor itself. For this reason, all components of the system should always be included when troubleshooting. Noises are caused not only by the compressor, but also by its fastening, the drive, the expansion valve or the lines. An incorrect quantity of refrigerant can also be responsible for various noises. In relation to this, there is the separate technical information. Noise development. The technical information Compressor damage provides information about different types of compressor damage and their causes.
In addition, the oil provides important information about possible damage:

  • If the oil in the compressor has taken on a red colour, this may be attributable to much moisture.
  • Oil with a black colour points to a defective compressor.
  • Silver-grey oil should be checked for metal swarf. The greyish discoloration points to metal abrasion.

As the system oil quantities become ever lower (sometimes only 80 ml), the monitoring and observance of the oil quantity is of great importance (e.g. during air-conditioning servicing and when replacing components.

The repair of clutchless compressors is possible only to a limited extent. It is essential that suitable tools and repairinformation are used when carrying out such a repair. Of course, assessment of the system pressures is very important when carrying out diagnosis work. In relation to this, the specified values of the vehicle manufacturer should be consulted.

This also applies to the blow temperature. Guidelines in relation to the assessment of system pressures can be taken from the table below:
Screen Shot 2017-05-18 at 15.56.31

Compressors without magnetic clutches

General

Screen Shot 2017-05-18 at 15.27.04For some years, so-called clutchless, externally triggered, variable compressors have been used (Fig. 1). All well-known compressor manufacturers use a great variety of different basic types. Here is a list of the most common types on the market: Denso, with the types 6SEU & 7SEU, Sanden, with the types PXE 13 & PXE 16. However, Delphi/Harrison is also represented via the CVC7 series, the design of which is very similar to the V5 compressor. This generation of compressors is used by almost all vehicle manufacturers (Audi, BMW, Citroen, Seat, VW, Opel). Externally triggered means that the stroke volume of the compressor is determined by a built-in control valve that is triggered by the air-conditioning control unit, depending on a wide variety of system parameters such as outside/desired temperature, high/low pressure, rotational speed, engine load. Clutchless means that the compressor no longer has an electromagnetic clutch. This means that the compressor is permanently driven via the pulley and works even if the air-conditioning system is switched off. However, in relation to this, the power is regulated down to a few percent.

Screen Shot 2017-05-18 at 15.28.06Operation

The pulley unit of the compressor consists, for example, of a drive plate and the actual pulley (drawing). The drive plate consists of a rubber element and forms the connection between the pulley and the compressor shaft. It acts as a vibration damper and also protects the compressor or the other driven units from overload or damage. If the compressor should lock up for example, the transmission forces between the pulley and the drive plate increase considerably in the area of the rubber element.

Depending on compressor manufacturer or type, the connection is interrupted by the deformation of the rubber element or by the triggering of an overload protection . The pulley then simply runs freely. This prevents damage to the belt or other units driven by the belt.Screen Shot 2017-05-18 at 15.36.42

The control valve (Fig. 2) is located in the compressor and receives its pulse-width modulated signals (PWM) from the air-conditioning control unit. The current which is fed from the control unit to the control valve, and which ultimately determines the power of the compressor, can be displayed as a measured-value block with the aid of diagnosis equipment. Clutchless compressors also have a safety valve (Fig. 3), which is intended to protect the compressor and the other
components of the air-conditioning system from excessive pressure. The valve usually triggers at a pressure between 35 and 45 bar (depending on the compressor manufacturer). The valve opens only until the overpressure has reduced. Afterwards, it closes again, so as not to release the entire quantity of refrigerant into the atmosphere. If the film of the valve is damaged, it can be assumed that the valve has triggeredScreen Shot 2017-05-18 at 15.37.23

Diagnosis

The pulleys and their rubber elements that are designed as overload protection are,
depending on the compressor type, designed differently. Depending on the type, it is possible in different ways to determine whether or not the overload protection has
been triggered:

  • Rubber abrasion parts are visible on the inside of the pulley (Fig. 4). The compressor shaft is no longer driven. Provided that the compressor can be turned easily, the pulley and the rubber element can be replaced.Screen Shot 2017-05-18 at 15.39.23
  • The over load protection has triggered the drive plate (Fig. 5). The drive plate and the rubber element can be replaced individually.
    Prerequisite: The compressor can be turned easily.Screen Shot 2017-05-18 at 15.39.58
  • A triggered torque limiter cannot necessarily be detected visually. In order to check whether the limiter has triggered, the compressor shaft must be held using a suitable tool (Fig. 6), and, at the same time, the pulley must be turned to the left. If the pulley can be turned to the left, the limiter has triggered and the compressor must be replaced. In the case of compressor types Sanden PXE 13 and PXE 16, replacement of the torque limiter is not possible.

Screen Shot 2017-05-18 at 15.45.22
In the case of the Audi A3 for example, at the lowest temperature setting, the maximum current that is fed from the control unit to the control valve is approximately 0.65 A. In relation to this, the compressor reaches its maximum power. In regulating operation, an average current of 0.3 A flows. In the case of newer vehicles, however, the problem is that diagnosis outside the engine-management area is not yet possible with many testers. Here, ideally, the use of an oscilloscope is helpful. With the aid of suitable test peaks, the PWM signal at the plug connection of the compressor can be recorded. In relation to this, the oscilloscope should be set to 5 V/div and 0.5 ms/div. With the engine running, the individual modes of operation can now be depicted on the screen of the oscilloscope. In the case of the lowest temperature setting ( Lo ) a square wave signal with a duty factor of approximately  75% (Fig. 7) is shown. The duty factor results from the ratio of pulse width -B- and the signal distance -C- (in this case 75% operating time, 25% switch-off time). At the same time, a readout of the level of the vehicle-electric-system voltage (approximately 13.5 V) can be taken on the basis of the volt divisions (A=5 V). The voltage value(9.8 V) displayed as a number is simply an average value. The pulse width depends on the desired cooling performance and the vehicle-electric-system voltage. Over the distance of the area -B-, the current to the control valve from the control unit is regulated . Depending on the setting of the control panel and ambient influences (e.g. outside temperature) the pulse width of the square wave signal is changed in such a way, or the control valve is triggered in such a way, that the compressor power necessary to reach the desired temperature is produced. Fig. 8 shows how, in the case of the temperature setting High, the compressor is regulated downwards. Fig. 9 was recorded in Econ operation (compressor off) and shows no signal. On the basis of these methods, it can be determined to what extent asignal change takes places through the control unit. If a plausible change of the signals takes place, but no change in the blow temperature or lowering of the interior temperature results, the compressor is probably faulty.Screen Shot 2017-05-18 at 15.45.52

Screen Shot 2017-05-18 at 15.46.34
In addition, there is diagnosis equipment on the market with which it is possible to generate a PWM signal with a different pulse duration. Thus, it is possible to determine whether a triggering of the compressor leads to a change in the refrigerant pressure. This serves as the basis for being able to make a statement as to what extent the compressor still functions perfectly.Screen Shot 2017-05-18 at 15.47.30

A functional check by means of a PWM signal can also be carried out using a function generator (Fig. 10). For this, it is however essential to connect a load which corresponds to that of an electronic control valve to the control-unit side of the air-conditioning system. Otherwise, the control unit will detect a fault in the system and will store this in the fault memory. This can lead to malfunctions or to failure of the system. In this case, a readout of the fault memory must be taken and
deleted using diagnosis equipment.

Screen Shot 2017-05-18 at 15.47.51
Again and again, complaints about compressors are hastily filed in connection with noises and other problems of air- conditioning systems. In very many cases, it turns out that the compressor  is alright, or that the cause of the fault does not stem from the compressor itself. For this reason, all components of the system should always be included when troubleshooting. Noises are caused not only by the compressor, but also by its fastening, the drive, the expansion valve or the lines. An incorrect quantity of refrigerant can also be responsible for various noises. In relation to this, there is the separate technical information. Noise development. The technical information Compressor damage provides information about different types of compressor damage and their causes.
In addition, the oil provides important information about possible damage:

  • If the oil in the compressor has taken on a red colour, this may be attributable to much moisture.
  • Oil with a black colour points to a defective compressor.
  • Silver-grey oil should be checked for metal swarf. The greyish discoloration points to metal abrasion.

As the system oil quantities become ever lower (sometimes only 80 ml), the monitoring and observance of the oil quantity is of great importance (e.g. during air-conditioning servicing and when replacing components.

The repair of clutchless compressors is possible only to a limited extent. It is essential that suitable tools and repairinformation are used when carrying out such a repair. Of course, assessment of the system pressures is very important when carrying out diagnosis work. In relation to this, the specified values of the vehicle manufacturer should be consulted.

This also applies to the blow temperature. Guidelines in relation to the assessment of system pressures can be taken from the table below:
Screen Shot 2017-05-18 at 15.56.31