Car AC Pressure Switch Testing

by Anthony Faccenda
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Auto air conditioning pressure switch testing allows you to diagnose potential or existing AC problems. Pressure testing the vehicle's low and high ports, which are connected to the AC compressor, is beneficial in regard to thermometer, compressor, leak detection and refrigerant diagnosis.


Older model vehicles require R12 AC gauge sets, while newer models use an R134a AC system. You may begin reading either pressure port after you determine your vehicle's appropriate gauge requirement.The low pressure gauge should be able to read from zero to 30 inches of vacuum Hg, and zero to 250 psi. High pressure gauges should be capable of reading zero to 500 psi.

Low Pressure Readings

Low pressure AC readings are critical in diagnosing temperature output problems. A low pressure reading higher than normal may indicate a faulty compressor or refrigerant overcharge. A lower than average reading likely indicates an incorrect amount of freon.

High Pressure Reading

Higher than normal high pressure readings could mean that there is too much system air, airflow restriction and/or too much refrigerant. Poor airflow may indicate an AC condenser problem. Low high pressure readings usually indicate low refrigerant levels. Irregular pressure reading may also signify "worn parts" within the AC compressor.

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