For the first time yesterday my central air unit tripped its breaker. I turned it back on and didn't think anything of it until later that night when the thermostat wasn't calling for cold air, and the outside fan was still running.

Took the cover off today and found the Start Capacitor totally blown apart. I cleaned it out and found one online for about $35... not a big deal, but here is my question:

-By looking at the wiring diagram and doing a little google-ing, it seems that the start cap only helps get the motor up to speed quickly and then does nothing when the motor is running (makes sense why the thing still runs). If the contactor is bad, does anyone know how I could tell that? Everything looks fine to me with the thing (i.e. no burnt connections... nothing looks fried). I don't want to turn the breaker back on and try to probe the thing while its running without knowing exactly what I'm doing. Is there any chance that replacing the start cap will fix the problem? I have a sneaking feeling that there will be more involved here because the cap shouldn't have anything to do with the unit turning off correctly.

Thanks for the help

Besides the main contactor that engages power to the entire condenser unit, there should be a smaller starting relay in there. Its purpose is to remove the start capacitor from the circuit once the compressor motor is running. This relay is normally closed, and if it fails to open I could see this causing the capacitor to blow up.

Two possibilities are:

The contacts are stuck together
Try moving the relay contacts to see if they can actually separate.
The coil is open
Test this with a ohmmeter. Not sure of the reading, but it should not be open.

These steps may be best done after removing the relay from the unit.

You've done a lot of good detective work so far. Don't screw it up and forget to TURN OFF THE POWER while working on this.

Best of luck,
WallyH

Hi Wally,

Thanks for the advice, I replaced the cap and found that the contact was stuck together. I freed it up and it is working perfectly again. Thanks for the help, just thought u would want to know the outcome

Craig

Thanks for the follow-up... it adds greatly to the thread value when we know how it turned out.