To test a compressor, primarily an HVAC or AC compressor, follow these steps:
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Safety First: Turn off the electrical power to the unit, using the electrical disconnect or breaker to avoid shock.
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Initial Electrical Testing: Use a multimeter on the compressor wires (usually three: common, start, and run). Measure the electrical resistance between pairs of wires to check the windings' condition. Typical readings:
- Lowest resistance between common and run
- Medium resistance between common and start
- Highest resistance between start and run
If you see open loops or inconsistent readings, the compressor might be damaged.
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Test for Short to Ground: Measure resistance between the compressor casing or a ground point (such as the copper tubing attached to the compressor) and each wire. An infinite resistance (open loop) indicates no short; low resistance indicates a short to ground.
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Physical Inspection: Look for visible damage on the compressor, burnt wires, or leaking refrigerant around any seals or plugs.
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Testing with Pressure Gauges: Connect gauges to the system's high and low pressure valves to measure operating pressure and identify abnormal conditions.
This accurate testing sequence with a multimeter and pressure gauges helps determine if the compressor is functional or faulty and if it needs replacement or repair. Additional care is needed when handling refrigerants or electrical components. This procedure is applicable for single-phase compressors but general guidance applies to other types as well.
