HVAC will cycle on and off properly. PLEASE HELP! THANKS!

[Goatkeeper]

Briefly, we have a 2008 Holiday Rambler Admiral with dual Brisk Air heat pumps and a gas furnace run through a SINGLE Duo-therm 5 button CCC 3109228.019. We were at a campground hooked to 30 amp service, we left for a few hours with only front A/C running and more than likely had several voltage drops from to many units, but upon our return the front A/C was not working. Service guy came and replaced fan motor and control box.

Since that time, HVAC will not cycle on and off properly.

FRONT UNIT: In A/C mode, unit will turn on when thermostat is turned below 70 deg, will run and cool properly BUT not turn off until you manually raise the CCC to 72 degrees, even when temperature setting has been reached or bypassed! Then unit shuts off almost immediately. In Heat mode, basically just the opposite happens, you must set the CCC to 72 or above to turn on, unit will run and heat normally, but never turn off until the setting on CCC is manually changed to 70 degrees, even if tempature reached 85 degrees! Same thing happens with furnace, with one exception…the furnace burner will cycle on and off, but fan will never stop until you manually reduce thermostat setting to 70 deg. Then fan runs in proper cool down mode for a minute or so and then shuts off.

REAR UNIT: The rear Heat and A/C operates semi-normally! By-the-way, it was turned off during the low voltage incident! The unit seems to function normally, except that it also has a “temperature number that it likes!” What I mean is, it will function in HEAT MODE if you set the thermostat to 73 degrees or warmer. It will run, heat and cut-off properly! BUT, if you set the CCC to 71 degrees, it will never turn on! ALSO, if the front HEAT is running and you then set the rear unit to run, it will not turn on until you raise the setting to 80 degrees or more!

Please understand that while I am not a HVAC person (although I have now learned way more than I ever cared to know!), I am a mechanical engineer. We have used temp probes to verify that requested temp is either less or more than ask for. Our rear remote sensor has always been about 2 degrees warmer than front.

This is a list of what has been tried:

Two new thermostats have been tried…with no change to problem!
12 DC current is correct to thermostat (12.50v) and CCC (11.41v)
Run capacitors exchanged, front to rear…no change to operation
Original control board was tried…functioned same as new one. Rear control board was moved to front unit…no correction to problem
Wiring traced…appears correct
Replacement fan is correct part number
Control boards are correct numbers 3109226.005
No shorts appear in 12 volt wiring to thermostat
CCC reset each time disconnected or dip switches changed

Did not replace start capacitor or PTCR…was not sure if they might affect fan operation

The initial service tech never came back. The local dealer where we were contacted Dometic and they said it was a CCC issue, hence first new CCC! We have since had to come to Texas and I contacted two local mobile repairmen and BOTH said it had to be thermostat, so I went to local dealer and talked to Service Manager. He confirmed it had to be thermostat! Hence second CCC. Needless to say, it don’t work!

Anyone have a fix? Suggestion?
Thanks!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!

[sparkydog]

It sounds like you may need reset the 5 button thermostat. There is sequence on dometic web site. That's the first I would try, I've had to do it on several occasions.

[Goatkeeper]

Thanks sparkydog, I knew I was forgetting something in the list of items tried (have since corrected and add this). I had to tell the first repairman about this and how to perform the recalibration...only because I had read the instructions!

[itdave]

Has anyone looked at the actual temperature near the front and rear remote temperature sensor. I am not sure where your sensors are located but in my coach there in locations where they are impacted by outside temperatures and location of the ducted vents. I would suggest that you get a new remote sensor and plug it into the inside AC unit control board to see if that changes the problem.

[Goatkeeper]

Thanks itdave! Yes we have checked temps with digital heat probes and the rear sensor seems to be working near correct temperature. The front sensor is in the CCC and it does not seem to be functioning. Like I stated we have tried the original and two new CCC's and all act exactly the same...heat on at 72, must manually change CCC to 70 to turn off. Otherwise it runs on...several times exceeding 85 degrees in coach. AC is opposite...70 to turn on and 72 to turn off. Will cool coach to 65 or colder and still run. It is almost like there is no automatic mode anymore...just manual on and off!
Thanks again!

[itdave]

Since the remote sensors first connects to the A/C unit is it possible the board in the unit has failed?

[H. Miller]

Wish we could help with the a/c problem but would like to point out that this situation is the perfect reason for installing a $250. energy management system (Progressive Ind. or otherwise). Incoming low and high voltages are shut down along with many other problems identified.