A/C System Components and Functions

System Components:
The A/C system components are specially designed for R134a refrigerant. The system components are:
1. Condenser
2. Compressor
3. High-pressure and safety switch
4. Temperature switch
5. Evaporator
6. Low-pressure switch ("Pressostat")
7. Receiver/dryer
8. Filler valve
9. Quick-release couplings
10. Expansion pipe (orifice)
- Quick-release couplings (9) are used for the evaporator connections and connections to the receiver (dryer) if any. Special tools are required to undo these couplings.
- The plastic rings on quick-release couplings are there to show that they were correctly fitted at the factory.
- The compressor is fitted with a temperature switch (4) which cuts power to the compressor if it overheats,if the temperature rises above approx. 105 °C (221 °F), e.g. if there is a refrigerant leak. Power is restored once the temperature has returned to normal, around 90 °C (194 °F).

Systems With R134a:
As A/C systems with R134a need a certain amount of special treatment, there is a decal on the right-hand wheelhouse and a yellow plastic ring around the filler cap (8) marked "R134a".
For systems with R134a:
- Under no circumstances may other refrigerants be mixed with R134a.
- Special PAG oil must be used when refilling the compressor.
- Since the system absorbs atmospheric moisture very readily, connections must be plugged as soon as they are opened.
- Instead of the ETF and service valves, there is a filler cap of different dimensions to line with international standards (SAE).

Points To Note When Working On System:
It is essential to fill the system with exactly the right amount of refrigerant. Too much or too little, and performance will deteriorate - and, in extreme cases, the compressor will be destroyed.

Using anything other than special PAG oil runs the risk of breaking the compressor.

Avoid exposing the system to air for any longer than necessary: plug connections immediately when removing a component. If the system is open to the air for more than about 10 minutes, you will need to replace the receiver (drier).

Recycling equipment should always be used when servicing system.

Use The Right Refrigerant:
Filling the system with the wrong refrigerant will destroy a number of components:
- The compressor will overheat and malfunction, because the oil used with R134a is unique. Other oils are not miscible with R134a, losing the lubricant effect.
- The working temperature will be too high, destroying hoses and seals.
- The receiver/dryer will not work properly, as it contains a drying agent designed specifically for R134a.
- Likewise, an A/C system designed for R12 will be destroyed if filled with R134a.

Compressor:
Compresses the refrigerant in gaseous form. Gas emerges from the compressor at high pressure 10-25 bar (145-362 psi) and temperature 65-105 °C (149-221 °F).

Condenser:
A heater which cools the refrigerant to liquid form (condensing). Fluid leaves the condenser at higher pressure 9-24 bar (131-348 psi) and lower temperature 40-80 °C (104-176°F) than from the compressor.

High Pressure And Safety Switch:
This has three functions:
- It shuts off the compressor if pressure in the system rises too high, more than approx. 30 bar (435 psi).
- It shuts off the compressor if pressure gets too low, less than approx. 2 bar (29 psi).
- It sends a signal to the engine management system to start the radiator fan. If the pressure is over approx. 16.5 bar (239 psi), one of the pressure switches closes and the radiator fan runs until the road speed is over approx. 65 km/h (40 mph). This cools the condenser more effectively and maintains the A/C system performance.

Expansion Pipe (Orifice):
A choke which reduces refrigerant pressure and temperature to enable it to evaporate at room temperature. After passing through the expansion pipe, the media is partly in liquid form and is at low temperature approx. 3-6 °C (37-43 °F).

Evaporator:
A heat exchanger which evaporates refrigerant, i.e. heats it and vaporizes it. It takes the heat it needs from the air. The cool air then passes into the passenger compartment. The evaporator emits gas and a small amount of liquid at low pressure 1.5 to 3 bar (22-44 psi) and low temperature approx. 2-5 °C (36-41 °F).

Low Pressure Switch:
The low pressure switch (Pressostat) senses the pressure of the refrigerant leaving the evaporator, i.e. on the low-pressure side of the system. If the pressure is too low, less than approx 1.6 bar (23.21 psi), the A/C compressor shuts off and restarts once the pressure rises again (over approx. 3.1 bar [45 psi]). If it did not shut off, the evaporator would cool down so far that the condense water in it would freeze.

Receiver (Dryer):
From the receiver (dryer), gas exits at low pressure and temperature 0-10 °C (32-50 °F). The receiver (dryer) has a four-way function:
- It removes any moisture from the refrigerant using a drying agent.
- It tops up the refrigerant if there is a leak.
- It separates any drops in the refrigerant so that only gas passes to the compressor.
- It returns oil to the gas passing to the compressor.

More Details About R134a:
Known as PAG (Poly-Alkylene Glycol), the oil which circulates in the compressor and A/C system has been developed specially for R134a. Satisfactory lubrication requires that the oil be miscible with the refrigerant.

R134a operates at a maximum temperature approx. 10 °C (18 °F) lower than R12 and at a pressure approx. 2 bar (29 psi) higher.

R134a lack of ozone-depletion potential is attributable to the fact that it contains fluorine rather than chlorine.