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A/C Compressor coil burnt up?

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. 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.

There is a run capacitor across the S and R terminals of the compressor. No start capacitor. This is a permanent split capacitor type hookup where both run capacitor and start winding stay in the circuit during start and after the motor is up to speed...

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 start coil burned up? If the start coil is burned up, is there any way to start the motor using the run coil and some external whizardry?

See figure 4-13 of

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where the start winding has a series resistor...maybe its in case the run capacitor shorts it would cause the thermal protector to trip... protecting the start coil? The C terminal has an internal thermal overload to protect the run coil.

There is no (apparant to me) low-pressure cutoff switch on the unit.

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.

--
gado
Reply to
gado
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S, R, and C should all be low ohms.

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gado writes:

Reply to
Sam Goldwasser

Your description of the system (a single capacitor) indicates that you have a PSC compressor.. not a CSR type. A CSR type would have both start and run capacitors. You have 2 ohms between the C-R terminals, indicating that the run winding is probably OK. If the resistance between the S-R terminals is that high, that indicates that the start winding is open. Time for a new compressor. Or a new A/C unit {:

Reply to
DaveM

Your compressor has a burned out start winding, it probably locked up from sitting or short cycled.

Reply to
James Sweet

Did you measure S-R at the compressor terminals (removing any protective cover that might be in place) or did you measure at the contactor terminus?

Reply to
Travis Jordan

Also measure C-S at the compressor terminals and report back.

Reply to
Travis Jordan

Travis,

I measured high resistance across the terminals of the run capacitor.

So I removed the plastic cover to gain access to the compressor terminals. A different story here. C-S is 4.6 ohms, C-R is 2.5 ohms, S-R is 2.2 ohms but sometimes 6 ohms (these may be a little mixed up as I did the measurement in the dark using a flashlight and inspection mirror to place the alligators on the terminals...)

I'm going to try to replace the 35 uF 440VAC run capacitor, its terminals are quite rusty. I thought about sanding the terminals but as long as I am this far in I might as well replace it.

I removed the leads and got a low reading from the capacitor contact to the compressor so I think the wire is ok, doesn't feel brittle and no charring of the insulation)

Thanks for the idea!

Gado

--
gado
Reply to
gado

There's no way a bad capacitor will give you a higher resistance reading than the terminals it connects across. You've got a bad connection somewhere.

Reply to
James Sweet

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