When electrically inspecting or troubleshooting a compressor, you should always protect yourself against the possibility of terminal venting. This occurs when an electrical terminal of a compressor blows out and vents the refrigerant within the compressor and the system. Usually you discover this after the fact. Typically, you are called out for a system that is not cooling, only to discover the system has lost its entire refrigerant charge and one of the compressor terminals has blown out.
There is always the possibility of this occurring while electrically testing a compressor charged with refrigerant, so always stand to the side when placing your meter leads onto the compressor’s terminals. Never look straight at terminals; you would not want a terminal blowing out during this time. There could be sufficient force behind the terminal to cause serious injury. I have actually seen a manufacturer state in their literature not to electrically test a compressor unless you remove the refrigerant first. Not a very practical option, but it would always prevent this type of injury.
To further prevent yourself and others from injury, always make sure to reinstall the compressor’s terminal cover; do not leave the cover off. I have been on many jobs where the cover is either completely missing or off to the side. Sometimes reinstalling the cover plate is challenging, but it is important to always reinstall it. It would be nice if manufacturers would make it easier to take off the covers and reinstall them, but we need to work with what we have.
While servicing a compressor, you should also always make sure its electrical connections are tight. A loose electrical connection could result in a failed system and an unnecessary return visit. This is definitely a preventable failure and should be checked while working on the compressor.
Another issue you may have to deal with is a compressor with damaged or corroded terminals. Depending on the extent of the damage, you may not be able to reconnect the wiring to the compressor. They do sell terminal repair kits that could be used, but if the damage is too extensive, the compressor will need to be replaced.
While servicing and repairing single-phase hermetic compressors, you may need to identify the electrical terminals of the compressor. Normally this is done by measuring the resistance across each terminal. The highest resistance measured will be across the run (R) and start (S) terminals. The next highest resistance will be across the common (C) and start (S) terminals. The lowest resistance measured will be across the common (C) and run (R) terminals.
To make identifying the electrical terminals a little easier, many U.S. compressor manufacturers follow a standard terminal configuration. The standard terminal configuration of C-S-R is read from top to bottom and left to right. Even though this configuration is widely accepted, it is always best to confirm the electrical terminals by measuring the resistances across each terminal.
So remember, next time you are inspecting the terminals of a compressor, be mindful of the possibility of the terminal venting and always re-install the compressor’s cover plates.