System Protection

From the condenser the liquid passes into the Receiver-Drier which has three functions:

• Storage vessel for varying system refrigerant demands.
• Filter to remove system contaminants.
• Moisture removal via the desiccant.

With the passage through the receiver-drier completed the, still high pressure liquid refrigerant, enters the Expansion Valve where it is metered through a controlled orifice which has the effect of reducing the pressure and temperature.

The refrigerant, now in a cold atomised state, flows into the Evaporator and cools the air which is passing through the matrix.

As heat is absorbed by the refrigerant it once again changes state, into a vapour, and returns to the compressor for the cycle to be repeated (Fig. 5).

There is an automatic safety valve incorporated in the compressor which operates should the system pressure be in excess of 41 bar. The valve re-seats when the pressure drops below 35 bar.

Note: The division of HIGH and LOW side is simply the system pressure differential created by the compressor discharge (pressure), suction (inlet) ports and the relative inlet and outlet ports of the expansion valve. This differential is critical to system fault diagnosis and efficiency checks.

System Protection

The trinary pressure switch, located in the liquid line, cuts electrical power to the compressor clutch if the system pressure is outside of the range of 2 Bar (1st Function) to 27 Bar (2nd Function). The third function is to switch on the cooling fans when pressure exceeds 20 bar.

General System Procedures

Leak Test

Faults associated with low refrigerant charge weight and low pressure may be caused by leakage. Leaks traced to mechanical connections may be caused by torque relaxation or joint face contamination. Evidence of oil around such areas is an indicator of leakage. When checking for non visible leaks use only a dedicated Refrigerant E134A electronic analyser and apply the probe all round the joint connection. Should a leak be traced to a joint, check that the fixing is secured to the correct tightening torque before any other action is taken.

Do not forget to check the compressor shaft seal and evaporator.

Note: Never use a dedicated CFC 12 or naked flame type analyser.

Charge Recovery (System Depressurisation)

The process of refrigerant recovery depends on the basic characteristics of your chosen recovery-recycle-recharge equipment, therefore, follow the manufacturers instructions carefully. Remember that compressor oil may be drawn out of the system by this process, take note of the quantity recovered so that it may be replaced.

CAUTION: Observe all relevant safety requirements.

• Do not vent refrigerant directly to atmosphere and always use approved recovery-recycle-recharge equipment.
• Wear suitable eye and skin protection.
• Do not mix the refrigerant with CFC 12.
• Take note of the amount of recovered refrigerant, it indicates the state of the system and thus the magnitude of any problem.