Fault-Tracing, Repair

Fault-tracing, repair





Checking the capacity and function of the air conditioning system

Compressor
In principle there are three reasons for a compressor not starting:
- a fault in the magnetic clutch.
- incorrect pressure in the system (too low or too high).
- fault in the wiring or the compressor control system.

Performance test
The performance test provides an indication of the air conditioning system capacity. During the test the temperature of the air flowing out of the center dashboard vents is measured under predetermined conditions (engine speed (RPM), fan speed, control settings etc).
If the capacity is too low this may be due to a number of "external" reasons, for example
- slipping compressor drive belt.
- insufficient air flow to the condenser (blocked by insects/dirt, foreign objects).
- poor engine cooling fan (FC) function.
- insufficient air flow to the climate control system (duct blocked by leaves etc).
- poor blower fan function.
- incorrectly adjusted control/damper/water valve for airflow - recirculation - temperature.
Too low capacity can also be caused by "inner" causes (faults in the system).
Initially this is checked by:
- visual check (damage, leakage. In the event of leakage there is often excess oil = greasy surface).
- listening (there is always a little noise in the system when the refrigerant changes between gas and water form at different pressures).
- feeling the components (if there is cold/warm air, how cold/hot they are).
- measuring the pressure in the system (if possible measurements should be taken on both the low and high pressure sides).

General repair instructions





Caution! Moisture (water) in the system is the worst enemy of an air conditioning system.

Remedy immediately!
Any leakage must be remedied immediately in order to prevent moisture, air or foreign particles entering the system. In addition it is vital that working conditions are kept clean and dry.
If dirt has entered any component it must be cleaned or replaced.
In the event of collision damage, all components that may have been damaged must be checked thoroughly. Soldered joints must be checked extra carefully.

Note! Damaged hoses/pipes must be replaced. They must not be repaired.

Use plugs!
Protective plugs must be used as soon as a connection is separated. The plugs must be removed as late as possible (directly prior to connection).
This is especially important for the receiver drier and evaporator.
A plug kit is available as a replacement part.
The oil is hygroscopic (= moisture absorbent) and must therefore be stored in a seal container. This is especially important for PAG oil.

O-rings, threads
If a connection is taken apart the O-ring(s) must be replaced.

Note! Different O-rings depending on the type of refrigerant.

O-rings and threads must be lubricated with the correct type of oil prior to installation.

Caution! The ability of O-rings to seal is dependent on them being lubricated.

Replacing the receiver drier
If the system is opened the receiver drier must be replaced:
- if air has entered the system for longer than 10 minutes.
- if it is suspected that there is moisture in the system.
- if the receiver drier is more than 1 year old.
The receiver drier should usually be replaced on most of the occasions that the system is opened.
This is because the drying agent is not reversible. It is not possible to extract water from the drying agent by vacuum pumping the system.

Topping up oil
Too much oil reduces cooling capacity.
Too little oil will damage the compressor.
The oil must be topped up when repairing a leak or when replacing a component.
The amount of oil required depends on the extent of the leak, whether it was large or small and on which components are replaced.
There are different oils depending on the type of refrigerant and compressor.

Some of the effects of too much water in the system
Internal corrosion ("rust")
Corrosive damage, applies in particular to systems with R12.
At high temperatures water functions as a catalyst for the break down of R12. Chlorine in R12 then compounds with the water and forms hydrochloric acid (=corrosive damage).
Poor power, interrupted operation (the compressor is disengaged for long periods).
The water freezes to ice at low temperatures and blocks the system, for example in the expansion pipe. As a result the pressure in the high pressure section increases and the safety switch disengages the compressor. It is then disengaged until the ice melts and the pressure has dropped.
Damage to the compressor (breakdown, reduced service life).
Liquids cannot be compressed so drops of water increase the load on the compressor.
Difficulties extracting the water from the system when vacuum pumping.
When the pressure sinks the water evaporates. Because pipes and hoses are poor conductors of heat, the heat (energy) required for evaporation is obtained from the water. As a result the water is over cooled and freezes to ice, blocking the system.

Safety information





Use overalls, goggles and rubber gloves
The refrigerant used has a low toxicity. The main risk is from frostbite caused by coming into contact with refrigerant. Protect your eyes and skin!

In the event of refrigerant coming into contact with eyes
- Rinse immediately with clean water for at least 10 minutes.
- Contact a doctor in the event of problems with vision or other difficulties.

In the event of refrigerant coming into contact with skin
- Rinse with warm water.
- Contact a doctor in the event of problems with vision or other difficulties.

Avoid high temperatures and mixing with air
Ensure that refrigerant does not come into contact with naked flames, welding, electrical discharges or hot metal surfaces etc.
Do not smoke when working with refrigerants.

Caution! Heated refrigerant can form irritating and toxic gases.

Caution! The pressure in a refrigerant container rises as it is heated. Do not expose a container with refrigerant to temperatures above 45°C (113°F) - risk of explosion.

Caution! Mixture of air + R134a at increased pressure (= above atmospheric pressure) is already flammable at a mixture of 50% air.

Equipment

A/C stations
To satisfy the legal requirements and to allow rational handling, Volvo has developed A/C stations which can be used to:
- empty the system and clean and recycle refrigerant.
- vacuum pump, check seals and top up the system.
The instructions for service and maintenance of the A/C station must be followed carefully so in order for it to function correctly.

Caution! Different refrigerants/oils must not be mixed. Therefore equipment adapted for the relevant refrigerant must be used. Otherwise there is a risk of damage to the equipment and to the system in the car.

Draining the system
The system (car) should have a temperature of at least 20°C (68°F). In cold climates the car should be taken into the workshop the evening before the work will be carried out.
The drainage time is reduced if the A/C system has recently been running and the engine is hot (radiant heat).

Vacuum pumping, leak testing the system
Any topping up of the oil in the system must be carried out prior to vacuum pumping.
This primary aim of vacuum pumping is to evacuate any moisture from the system. The low pressure means that the water evaporates and can then be sucked out of the system.
To ensure that all moisture is removed from the system, it is important that vacuum pumping continues for at least 50 minutes . In humid climates this may take even longer .
This other reason for vacuum pumping is to check that the system is sealed. When pumping is complete, the negative pressure may only be reduced minimally for approximately four minutes.

Caution! Water that is sucked up by the drying agent cannot be extracted by vacuum pumping.

Warning! Compressed air must not be used under any circumstances to leak trace a system with R134a. A mixture of air and R134a is explosive at high pressure and high temperature.

Topping up the system
Fill with the correct amount of refrigerant (the amount depends on the car and model year etc).
Too much refrigerant reduces the capacity. In addition there is a risk off refrigerant in liquid form reaching the compressor with increased wear/incidence of breakdown as a result.
Too little refrigerant reduces the capacity. In addition there is a risk off poor compressor lubrication (lack of oil) with increased noise/wear/incidence of breakdown as a result.

Leakage test
In addition to the vacuum method (vacuum pumping) a supplementary test must be carried out with a leakage locator after the system has been opened.

Note! The leakage locator must be adapted for refrigerant.

On hoses with PVC casing the casing must be removed and the hose with connections must be wiped clean prior to leak tracing.
This is because refrigerant diffuses (= forces its way out) through the hoses. The small amount that forces its way out is then collected under the casing and this amount may be sufficient to affect the leakage locator.

Performance test
After the system has been opened, a performance test must be carried out to check the function of the system and its capacity.