The outside A/C condensor unit (Trane TTJ type) of my home has a CSR-type compressor. It has two phase 120VAC fed to it. There is no (apparant to me) low-pressure cutoff switch on the unit. When the thermostat calls for cooling, the fan runs but not the compressor, even after it has rested for 24 hours. The A/C ran last summer. I just bought the house last year so I don't know the history of the unit or its maintenance. I took the cap off the freon return line and pressed the valve, there is at least some freon in the system but I don't have gauges to see how much pressure.

There is a run capacitor across the S and R terminals of the compressor. The electrical schematic diagram of the compressor shows a resistor (heater?) between the electrical coils of the S and R terminals.

The resistance between the C and R terminals is 2 ohms. The resistance across the S - R terminals (and the run cap) is between 1-4 megohms. I take it this means my run cap is not shorted. Based on the high resistance, is the S terminal open or the S coil burned up?

I have not measure the voltage to the compressor while the relay is engaged, so one of the relay contacts may be bad...but I thought I would try some meter probing first...

Gado