A/C problems

Rooftop A/C compressor won't come on. Fan works.
Where should I start looking? The capacitor?

Thanks,

2002 2720SL

[TrailManorMan]

That would be a start, they often fail after years of use. Most are reasonable also.

[Bill]

If you are competent to work with live houselhold electricity -
- AND I CAN'T EMPHASIZE THAT ENOUGH -
you might use a multimeter/DVM to check on whether power is actually reaching the compressor.

This requires crawling on the roof, to remove the air conditioner shroud, remove the inner covers over the electrical connections, and make the tests, so it is an inconvenient place to work. Get on the roof only when the TM is closed and latched down. Be sure to put down pieces of plywood to spread your weight. And make sure someone else is there watching you, just in case you get into trouble.

The capacitor in the compressor motor circuit is a likely candidate for failure, as already mentioned. However, I suggest checking power to the compressor motor simply because in some air conditioners, there is only one capacitor to serve both the fan and the compressor. Since the fan runs, there may be a different problem, such as a stuck-off overload sensor, or a bad mode switch. What model AC do you have? We could check the electrical diagram.

Bill

[Padgett]

Guess I think a bit differently. The roof AC pulls a lot of power on starting, even more if a bad capacitor keeps it from starting.

With an outside generator you should hear it grunt. On mains power I'd put a DVM on a 200vac scale and probe the AC plug by the fridge.

With that in sight, turn from fan to AC. You should see a dip of at least 5v and possibly as much as 20 when the compressor tries to start. If no dip, power is not getting to the compressor at all.

I just tested on mine which is currently on a 100ft 10 gauge extension cord to the normal TM cord. Running at 124vac/High Fan & switching to Low Cool I saw a momentary dip to around 110v then came back up to 120vac with the ac running. Thermo switch to max cold.

If you see a larger dip that does not come back, the compressor is not starting & the capacitor may be bad. Turn off immediately if you see this. If you see no dip, the compressor is not getting power. If the fan does not come on, you have a different problem.

ps once you turn the compressor off, wait a few minutes (five should be good) for the pressure to equalize before trying again or Bad Things may happen.

pps if you have the heat option installed (Lo Heat below Lo Fan) then turn the AC thermo all the way to hot and when turned from Lo Fan to Lo Heat you should see a similar but smaller drop.

[Bill]

Simpler solution, Padgett. I like it.

Bill

Thanks for the info.

I had that problem also... fan runs no compressor. My problem ended up being the thermostat was bad, local rv shop had a drawer full of them so I'm guessing that's a common problem.