Initial Inspection and Diagnostic Overview

For any refrigeration system to function properly all components must be in good working order. The unit cooling cycle and the relationship between air discharge temperature and ambient temperature and the pressures at the compressor can help to determine proper operation of the system.

The length of any cooling cycle is determined by such factors as ambient temperature and humidity, thermostat setting, compressor speed and air leakage into the cooled area, etc. With these factors constant, any sudden increase in the length of the cooling cycle would be indicative of abnormal operation of the air conditioner.

The low and high side pressures at the compressor will vary with changing ambient temperature, humidity, in-car temperature and altitude.

The following items should be checked before operating the system:
- Compressor drive belt tension.
- Compressor magnetic clutch operation.
- Condenser fan operation.
- Condenser fins (dirt will cause poor cooling and higher operating temperatures).

The following conditions should be checked after operating the system for several minutes:
- All high pressure lines and components should be hot to the touch.
- All low pressure lines should be cool to the touch.
- Inlet and outlet temperatures at the receiver/drier should be at the same temperature (warm). Any very noticeable temperature difference indicates a blocked receiver/drier.
- Heavy frost on the inlet to the expansion valve may indicate a defective valve or moisture in the system.
- With ambient humidity between 30% and 60%, compressor pressures and evaporator air discharge temperature should fall within the general limits given in the A/C pressure gauge chart.

A/C Pressure Gauge Chart:

A/C Pressure Gauge Chart

NOTE:
- Low and high side pressures are guides not specific limits.
- Evaporator air temperatures will be lower on dry days, higher on humid days.