An accurate diagnoses and determination of air conditioning system function and more importantly, malfunction, depend largely upon the ability of the technician to interpret gauge pressure reading. The importance of a refrigerant technicians’ manifold and gauge set is often compared to that of a doctor’s stethoscope. Your technician determines the quality of your A/C Performance Test.

Firstly, an improper gauge reading will relate to a specific a/c performance test problem. More than one problem may be associated with particular gauge reading, however. A system operating normally will have a low side gauge pressure reading that corresponds with the temperature of the liquid refrigerant as it becomes a vapor while removing heat from the air flowing over the evaporator coil surface. The high side gauge readings should correspond with the temperature of the vapor as it becomes a liquid while giving up its heat to the ambient air flowing through the condenser.

Secondly, any deviation from ambient dependent normal gauge readings, other than slight, indicates a malfunction. This malfunction, if within the system, may be caused by a faulty control device, a restriction or a defective component. It should be noted that improper mounting or location of components in a newly installed system may affect system performance. The vehicle engine may also affect system performance and will be noted as abnormal gauge readings.

Pressure readings are normal, A/C system is not cooling.

• • Warm air infiltrated into the evaporating unit or passenger compartment.

• • Warm water infiltrated in the heater.

• • Ice on evaporator core.

• • Normal situation if ambient temperature is very low.

• • Too little refrigerant quantity, 70-75% less. check for leaks.

• • (V) Expansion valve stuck partially closed or blocked

• • (V) Clogging in the H.P. or L.P. branch between filter and evaporator.

• • Blockage in the H.P. branch between compressor and condenser-filter hose, but before the H.P. reading point.

• • Normal situation if ambient temperature is very high.

• • Excess refrigerant charge, 30-5% more.

• • Condenser overheated.

• • Air present in the A/C system.

• • (V) Compressor displacement regulator valve defective.

• • Blockage in the H.P. branch between compressor and condenser filter hose, but after the H.P. reading point.

• • Compressor belt jumped. Probably caused by misalignment of the pulleys

• • Electric clutch of the compressor not engaged.

• • Compressor damaged.

• • (V) Compressor displacement regulator valve defective.

• • Suction and drainage hoses reversed on compressor.

• • Electric clutch of the compressor not engaged.

• • Expansion valve stuck open. If the compressor is “variable displacement type”, the low pressure has small but fast oscillations.

• • (V) Compressor displacement regulator valve incorrectly set or defective

• • Compressor damaged

• • Filter saturated with moisture

• • (V) Compressor displacement regulator valve stuck at maximum displacement.

• • (F) Blockage in H.P. or L.P. branch between filter and evaporator.