Suburban Furnace runs heater and A/C

[Bill_Scott]

(Posted on Tech Forum as well)

Just bought a new Forest River Hemisphere Fifth Wheel. Testing the furnace out because tomorrow night we are getting a freeze. Set the Dometic thermostat to FURNACE and the heat to 90 (just to test), After a few seconds, the AC comes on and blows cool air from the ceiling into the unit. After several more minutes the heat started coming out of the floor registers. Dropped the thermostat to 40 (the current temp is maybe 55-60). The furnace stopped heating, but the AC blower never stops blowing. Left it on for an hour and the AC blower is still blowing full blast. I can't figure out what is going on. So I turned the thermostat off and the AC fan finally stopped.

The last RV I had, I don't recall the ac unit blowing air at all when the furnace is turned on. Maybe someone else has had a similar experience.

 

[steveblonde]

Lol i have the same Dometic set up its wierd hopefully some one will chime in sorry im not near mine keep playing with it. I know it took me a while to figure mine out . Sorry i hope someone can simplify it for you
I
http://www.dometic.com/QBankFiles3/EPiServer/Dometic/US/Manuals/RV-manuals/Air-Conditioning/Single-Zone-LCD-Operation-Manual_17590.pdf

 

[Bill_Scott]

Thank you Steve. That did it. My dealer didn't include the Dometic thermostat manual or tell me how to program it. I have the installation manual for the furnace, but I do not have the operator's manual the documentation refers to. Makes me wonder what else I don't have.I will have a conversation with my dumba$$ dealer on Monday. Furnace is up and running, and AC is off thanks to you. The only problem I have now is to ponder, 'what nincompoop would ever want to run the AC and the furnace together, and why on earth does it appear to be the default'?  :-\

P.S.  I guess I might paraphrase Donald Rumsfeld when I say, "The problem is we don't know what we don't know."

 

[Gary RV_Wizard]

It's only the a/c fans that are running (or should be, anyway), and the idea is to circulate the heated air throughout the RV. Whether that is a good idea or not depends on how well the heat ducts are laid out in the RV.  It's not unusual for there to be hot and cold spots in some models & floor plans, and sometimes using the fans helps.

 

[Bill_Scott]

Thanks, Gary. That makes sense. But the constant howling of the fan makes it difficult to carry on a conversation in the living room. If the fan would stop when the correct temperature is reached it would be a better idea. We have a ceiling fan. Rather use that than the nosy A/C motor. I can only hope that the fan only comes on when the compressor is running, else we may have to stock up on earplugs.  :

 

[Linedog]

Mine was doing the same thing. Turn the T-stat to fan, set to AU (automatic) back to heat and the AC fan should not com on.

 

[Bill_Scott]

Thanks Linedog. Everything seems to be working now.