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shogun7
04-04-2004, 12:44 AM
One of the most important, overlooked and misunderstood compressor checks is a locked rotor voltage check. This is a reading of the voltage available to the compressor while it's attempting to start but failing to do so.
Here is a step-by-step procedure for checking locked rotor voltage:
1. Disconnect electricity to the air conditioner or heat pump at the fuse box or service panel.
2. Attach your voltmeter's alligator clips to the compressor's load terminals.
3. Stand back, well away from the compressor terminals.
4. Reconnect electricity to the air conditioner or heat pump.
5. Call for cooling.
6. Check the voltage reading while the compressor is humming or attempting to start, then disconnect the electricity at the fuse box or service panel.
If the locked rotor voltage reading is less than 197 volts, the problem is probably in the unit's electrical supply circuit. Check for:
· Undersized supply wiring.
· Excessive length of supply wiring.
· Loose or dirty connections in the supply circuit.
There is also a possibility that the problem is in the contactor. To check this out, check the locked rotor voltage with the voltmeter attached to the contactor line terminals. Compare the two voltage readings.
If the two readings match, the problem is in the supply circuit. If the line voltage reading is higher than the load voltage reading, it indicates high resistance through the contact points of the contactor. Replace the contactor.
Roger ;)