Originally Posted By: jpeck
This post was automatically imported from our archived forum.
It’s an “or”.
Most (if not all) compressors have crankcase heaters nowadays (I think).
The problem comes in when the temperature is below 60 degrees (65 just adds another safety factor) and the unit is not 'on' (not that it has been run, but that it is 'on' with power to it), leaving the oil cold and stiff. Cranking up the compressor then could damage the compressor.
If it is 60 or warmer, for that same 24 hour period, that should not be a problem.
If it is colder than 60 degrees but the a/c has been 'on' (again, not necessarily 'running' but have power to it) for 24 hours or more, the oil in the crank case is warm enough to work as intended and not damage the compressor.
Thus, it's an 'or', either makes it 'safe' to operate the compressor.
Now, if the breaker to the condenser (compressor) unit is OFF, you know the crankcase heater is also OFF, and that you do not want to operate it UNLESS it is 60 degrees (65 degrees is safer) or warmer, also for 24 hours. Then the oil is warm enough to operate the compressor.
Anyone out there who can explain it better than me, go for it (or correct me if I'm wrong in my explanation).