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TXredfish · 05-06-2011, 04:52 PM

My motorhome has 2 Dometic 13,500 air-conditioners which I take turns running when hooked up to 30A service. I don't run both at the same time.

Today, I had the (front) zone-1 = on and and (rear) zone-2 = off. Therefore, only the zone-1 A/C should be running. I notice from time to time while front is running the rear (zone-2) A/C compressor will come on for a few minutes and then shut off.
Also when running the zone-2 = on and zone-1 = off. Zone-2 A/C running and cooling OK and zone-1 A/C off. When temperature (78) is reached the rear A/C cuts off but compressor is still running for about 5 minutes and then turns off. When running front A/C and it cuts off after reaching desired temperature the front A/C and compressor cuts off at the same time.

To re-explain - both A/C will cool correctly. But when front runs by itself, and temp cuts off, both A/C and compressor cuts off. But still the rear A/C rear compressor will come on sometimes.

When rear A/C runs by itself and turns off, compressor keeps running for about 5 minutes. Front A/C compressor does not come on when only rear running by itself.

I don't think this is normal. Would a good cleaning of both top units solve this problem? Or could it be the Dometic control center thermostat or a bad compressor starting to go bad.

I hope these explainations make sense. Thanks for your help........

Gary RVRoamer · 05-07-2011, 07:37 PM

An a/c should never come on when it is turned off at the thermostat. Something is not wired correctly.

scenic route · 05-07-2011, 07:52 PM

TXredfish, I'm not real sure I'm following the problem. It's just that I've never heard my zone 1 or 2 system's compressor run independently from the squirrel cage fan before, so I don't know what that sounds like. I can hear the compressor kick in and out while the fan is running (when the fan is in low or high mode). If the selected zone's fan is in 'Auto' and the selected temperature is met, both the compressor and the fan will both kick 'off'. At the same time, if the selected zone's fan is in 'low' or 'high' mode, just the compressor will kick off and you can hear the difference...the fan will continue to blow. When the selected temp is not met, the compressor will kick back in with the fan until that temp is once again met...fan still on w/ the compressor off.

If your zone 1 or 2 'mode' is set to 'off', that zone should not run...in this mode(off), the fan button and the temperature 'up' and 'down' will be deactivated and that zone should be inop...no fan, no compressor. Could it be that although you do not have the 'non running' zone in 'cool' mode, you might still be in 'fan only' mode? This could be what you're hearing - especially if the fan is in the high or low mode when the other operating zone has achieved it's temp setting and kicks off.

I hope this helps and doesn't add to the confusion...this is how our system works. Good luck... Bob

TXredfish · 05-08-2011, 01:49 PM

An update to my A/C problem. Like I said front A/C works fine.
Motorhome set overnight with no A/C on and circuit breakers off.
I turned on front A/C circuit breaker. Front did not come on.
I turned on comfort control. I set comfort control mode to both A/C to off.
I turned on circuit breaker to rear A/C, rear A/C compressor came on right away for about 5 minutes and then shut off but no air from duct inside motorhome so I am fairly certain that it is compressor and not the fan. Also, since the MH was sitting overnight with no power, the A/C could not be freezing up.
It is odd that compressor would come on with comfort control mode set to off.
After this, I reset comfort control using procedure in manual by pressing zone button and mode button at the same time and turning on thermostat power button, until FF appears and release. Rechecked as above, still had same problem.
I set comfort control temperature on rear A/C to temperature to 74. It came on and checked air from duct at 58. So it is cooling OK. After reaching 74, rear A/C cut off but compressor still ran for about 5 minutes (no air from duct). I set comfort control mode to off. Compressor was still running. I then turned off comfort control power switch and compressor still running. I then turned off circuit breaker and of course no power to thermostat or A/C and A/C compressor turned off.

Basically, the problem is that compressor starts right away with no hesitation when circuit breaker is turned on. When A/C reaches desired temperature A/C fan turns off but compressor keeps running until circuit breaker is turned off.

Could this problem be the comfort control thermostat or low on freon or bad compressor? I am leaning toward thermostat control but is there a way to troubleshoot the comfort control other than purchasing a new one? But I could be wrong.

Thanks ...................

Mike Canter · 05-08-2011, 03:05 PM

I would suspect the control board in the AC unit. It is not because it is low on freon and not a bad compressor. It is what ever is controlling the AC unit. The thermostat just tells the unit to turn off or on.

If I understand you correctly you only have one thermostat. Is that correct?

TXredfish · 05-08-2011, 06:13 PM

Yes, I have one thermostat. But, it can control both front back separately.
It has a separate mode settings for each zone front and back). Each zone separately can be turned off using a mode setting, fan speed, temperature, etc. But has one power switch, which should turn off complete A/C system, thermostat and unit (compressor and fan). But when turning off power switch, rear compressor is still running (problem). Front compressor will turn off OK.

TXredfish · 05-11-2011, 07:49 PM

I had a retired RV repairman look at my A/C. He did some troubleshooting and determined that I had a bad relay on the control board. He ordered a control board from Dometic. I hope this fixes my problem. Thanks for your help.