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Thread: AC and furnace run at the same time???

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    AC and furnace run at the same time???

    We have a 2012 Greystone 33ck.
    When we are plugged in to power and turn the furnace on the AC fan kicks in and blows air out of the roof vents at the same time as the floor vents are blowing hot air. Is this normal or do we have a wire crossed somewhere??

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    Re: AC and furnace run at the same time???

    You need to scroll through the menu on your thermostat and set the fan to auto. It sounds like it is programed to either high or low.
    Plenty of people have had the same thing happen and it is an easy fix. I doubt you have a wire crossed.

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    Re: AC and furnace run at the same time???

    I think I've figured out why this is confusing. In our homes, there is one blower that pushes air for both A/C and heat. If it's on Auto, when the heat or the A/C comes on, the blower comes on. If you switch it to manual, the blower runs all the time to circulate air. In the RV there are 2 blowers: one for the furnace and the other for the A/C. The furnace blower comes on automatically and only when the thermostat calls for heat (regardless of thermostat fan settings). The A/C blower is controlled by the fan settings on the thermostat and comes on when the thermostat calls for A/C, or if the fan is set to run continuously in High or Low mode. We're all used to having a single blower controlled by the thermostat at home, but that's not what we have in our RV.


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    Re: AC and furnace run at the same time???

    So you are saying that there is both cold and hot air flowing into the unit? Is it possible that the lower vents are are just the blower kicking in, but it feels cold? Sometimes when I get confused like this I will look for an air conditioning Indianapolis company for help. Have you thought about doing this?
    Last edited by inthemidwest85; 09-07-2011 at 05:16 PM.

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    Re: AC and furnace run at the same time???

    We had close to the same issue, but it was the heater that was causing the A/C to come on. The furnace came on and would not shut off, once it got too hot the A/C kicked in. We found that the thermostat wire for the furnace had a short, but there was an extra one in the wire loom so I just switched it over. So far we are good with no issues.

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    Re: AC and furnace run at the same time???

    We are having the same issue. I will try putting the fan to auto to see if the air shuts off. This past weekend it was below 30 and we had to throw the AC breaker off to get just the furnace to run....I wish that the owners manuals gave you a little bit more on operations vs installation.

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    Re: AC and furnace run at the same time???

    Quote Originally Posted by Maggiemay View Post
    We are having the same issue. I will try putting the fan to auto to see if the air shuts off. This past weekend it was below 30 and we had to throw the AC breaker off to get just the furnace to run....I wish that the owners manuals gave you a little bit more on operations vs installation.
    Did you find a solution?? We just took delivery of our 2012 HL Big Country last Friday. The evenings here in SDiego are cool. When we turned on the furnace, the a/c also came on and blew cold air from the ceiling vents at the same time the furnace was blowing warm air from the floor vents. The dealership was 'going to look into it and get back to us' ... so far, no word. Trying to find a resolution on our own. Would appreciate any help...

    Thank you so much!
    Ken & Kat Atwood (Both Retired U.S. Navy)
    2012 Heartland Big Country 5th Wheeler


    UPDATE: After further research online, I have found a solution. To be clear, we have the Dometic thermostat. When I click the ON/OFF MODE button to turn on the furnace, the digital selector gives me the opportunity to adjust the FAN, COOL, and FURNACE settings. When you push the ON/OFF MODE button, make sure you see AU in the FAN selection. (There are three choices AU, HI, & LO. Make your selection using the UP/DOWN arrows.) For whatever reason, our thermostat was set to HI but once I changed the FAN setting to AU and then turned on the furnace, the problem was solved. No longer is cold air coming from the ceiling vents; ONLY the furnace is supplying hot air from the floor vents.
    Last edited by Katwoodx2; 01-21-2012 at 01:00 AM.

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