A/C & furnace control issues

Discussion in 'Towing, Vehicles, Maintenance and Repairs' started by TexasTrader, Feb 28, 2021.

  1. TexasTrader

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    Feb 28, 2021
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    1) Furnace will not turn off once setpoint is reached. We have to go to the thermostat controller and turn the unit OFF. Furnace then does normal shutdown. Furnace comes back on once we turn the thermostat controller back on.
    2) A/C will not turn on when setting thermostat to Cool / Fan Auto.

    Dometic 5 button Comfort Control Center Thermostat
    Suburban SF-42 furnace
    Dometic Penguin II low profile A/C

    Steps taken so far:
    Power cycled 12v system
    Power cycled 120V system
    Checked fuse for thermostat
    Replaced the thermostat (I had a back-up unit)

    Unique events recently:
    We are in Texas, and had a really cold spell recently with snow. These symptoms began during this cold spell.
    We also had short rolling blackouts for a few days.

    Any ideas on things to look at and troubleshoot would be helpful. Thanks in advance!
  2. BankShot

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    May 26, 2013
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    Hi and welcome to the forum. Sorry to hear you are experiencing problems with your AC and furnace. I am by no means an electrician but I do know a few things about what you are going thru. Those rolling blackouts you mentioned could very well be the cause of this. Power outages along with even "brownouts" can do weird things to the electrical system in an RV. The fact that the furnace does still run, just not properly means that the fuse for it has not tripped however in that the AC will not turn on could mean that the fuse for it has tripped? Also did you by chance check the main circuit board that is usually located in a storage bay? Something there could have been shorted out? If everything was working okay prior to the outages and cold weather, etc. chances are it is a fuse or even a capacitor, etc that can be changed out once found. Again, if you are unable to find the "culprit" best to get a pro to come check it out IMHO. I'm sure someone else on the forum with a lot more electrical knowledge will jump in shortly and possibly be able to add more assistance than I am able to give. Let us know when the problem is resolved and what the cause was as this will be of future help to others that may experience the same thing. Safe travels ahead to you. Also be sure and post a review of the RV parks and campgrounds you stay at, on the flip side of this site......

    Regards, BankShot..................(aka Terry)
  3. Rollin Ollens

    Rollin Ollens
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    Sep 17, 2007
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    I wish I could give you some concrete advice. My first suggestion would have been thermostat and obviously it was yours as well. The circuitry is simple but components in today's appliances can get complicated. If your problem was that the furnace would not run there are safety devices that could be the problem, high limit switches and such. Clearly, a message is not being delivered to say "turn me off" so that is where one must look. I suspect there is, built into your system, the means to not allow your AC to operate if the furnace is in use. A stab in the dark is that might be your AC problem. As BankShot suggested, me thinks this is the job for a pro.

  4. mdcamping

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    Jul 3, 2007
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    One small shot in the dark would be to cycle all power off, sometimes just unplugging & plugging the jack connections where the Tstat feeds to might do the trick, especially after having black outs or maybe brown outs in your area.

    sometimes aged low voltage connections, especially when exposed to constant temperature changes will build up pitting. As mentioned, chances are you will need a tech

    Good luck
    #4 mdcamping, Mar 3, 2021
    Last edited: Mar 3, 2021

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