120V Issue - One Leg Not Working

[JimNCheryl Domenoe]

We are on the road in humid Florida and have encountered a problem.  Last night the air conditioner (basement style) kept running but it was no longer doing much cooling.  I have since determined that there is no AC going to leg 1 of the AC circuit.  I checked shore power and it is not the problem.  I also ran the generator to see if I have two legs of 120V but that didn't change the outcome.

I have checked all of the breakers in the bedroom as well as the breakers in the box underneath (4 breaker switches in a gray box on the ceiling of the bay forward of the rear wheel, passenger side).

Is it harmful to run the air conditioner with only one leg of AC available?

If anyone has any suggestions, please let me know.  I am trying to find a mobile repair person, but no luck so far.  I will be in my current location until tomorrow and plan to hit the road to head north into Georgia.

Thanks in advance for any suggestions.

[Dick Simonis]

On mine, the fans both run on leg one power so if the fans run it would suggest that your problem is power to the 1st stage compressor not loss of the entire leg.  How did you test it.

Dick

[JimNCheryl Domenoe]

Well, I just read another post that made me try something else.  It seems that the thermostat fan switch was on low, and therefore, only one compressor will work.  I turned the system back on and put the fan switch to Auto/High and both compressors kicked on.

I still have a reading of OFF for AC Leg 1 on my CMP-10.  I don't understand why this is reading zero.  Leg 2 varies but it around 120-122. Both AC legs are drawing around 12 amps which seems right with both compressors running.

Maybe I am just missing something here.  I am not a pro at this by any means and I may have misinterpreted the meaning of these readings.

Jim

[Steve Huber Co-Admin]

Jim,
Sounds like the problem is with the CMP sensing of the AC leg rather than the AC itself. If your showing a 12A draw on each leg you've got AC on both.
Not sure where the CMP senses the voltage though.
Steve

[Frank Towle]

Jim, mine is located next to the automatic 120V relay in the same sized box.  Major electricity there from post, inverter or generator - BEWARE!  Could be bad/loose connection in box or connection to central CMP system.  Agree that if showing AMP draw of course voltage is there. 

[Edward Buker]

Jim,

There is a grey box on the ceiling of the bay next to the transfer switch as mentioned by others. That box has two circular toroid transformers with windings that sense the AC current. There is also a small standard transformer for each AC leg with I think a 10 to 1 winding ratios that converts the 120V to 12V for a sense module to interpret. You could check to see that the wiring is as it should be and measure the 120V side and then the 12V side on the transformer to see if it is working. If you have an open winding you could replace it if that is the problem. One of the small transformers should measure differently from the other, probably 0V AC on the secondary winding for the leg that is not working on the monitor panel. The number in the photo on the transformer would identify the replacement.

Later Ed