Furnace blowing cold from AC vents?

SeventyGTX · 01-01-2020, 03:27 PM

We are getting ready to trade in our 262RGX and since it's cold out, I decided to kick on the propane heater. It fired right up, and blew somewhat warm air out the heater vents at first, but it was also blowing cool air out the AC vents. Now it is just blowing cool air from the ceiling and the furnace is still on. The Dometic controller is set at 78 and it's cold in there! Any help it appreciated, I don't need the dealer to give me any reason to knock me down in trade.

Kimber45 · 01-01-2020, 03:48 PM

fan set to auto? have a heat pump that is on in to cold of weather?

Thurman · 01-01-2020, 04:02 PM

IF you have a Dometic digital t'stat you may need to set the t'sat to "AUTO", as Kimber stated

SeventyGTX · 01-01-2020, 04:15 PM

Thanks guys. I was just looking at the manual and didn't even know there was an auto setting. We rarely use it when heat is needed and only used the AC.

I went out and put it on auto, and it got rid of the cool air from the ceiling vents. But the bedroom and bathroom vents are barely blowing out anything. The kitchen floor vent it is doing ok. I'm sure it's ok, just had me spooked when it was blowing out the AC vents.

SeventyGTX · 01-01-2020, 04:17 PM

Quote:

Originally Posted by Kimber45

fan set to auto? have a heat pump that is on in to cold of weather?

We have no heat pump option that I saw with the mode switch. Our manual says that comes with "select models".

cavie · 01-01-2020, 04:58 PM

It will not say "Heat Pump" on the t-state. You 'll have to look up the model #. but if it cam on in the heat mode it is a heat pump.

Larry-NC · 01-02-2020, 03:53 PM

Quote:

Originally Posted by cavie

It will not say "Heat Pump" on the t-state. You 'll have to look up the model #. but if it cam on in the heat mode it is a heat pump.

Cavie, unfortunately, these new-fangled Dometic Thermostats integrate the heating and air conditioning more than the old, reliable mechanical thermostats did.

The design engineer was probably thinking "All the hot air will go to the ceiling and the travelers will get cold feet. Let's run the A/C fan for circulation whenever the furnace runs." Well, it turned out to be a bad idea. Moving air takes away surface heat from your skin and makes you feel cooler. With the maldesigned Dometic Thermostat the only way to disable that misfeature is to set it to "Auto."

SeventyGTX · 01-02-2020, 04:05 PM

Quote:

Originally Posted by Larry-NC

Cavie, unfortunately, these new-fangled Dometic Thermostats integrate the heating and air conditioning more than the old, reliable mechanical thermostats did.

The design engineer was probably thinking "All the hot air will go to the ceiling and the travelers will get cold feet. Let's run the A/C fan for circulation whenever the furnace runs." Well, it turned out to be a bad idea. Moving air takes away surface heat from your skin and makes you feel cooler. With the maldesigned Dometic Thermostat the only way to disable that misfeature is to set it to "Auto."

The Jayco we are getting has a Coleman. Hopefully it is a bit simpler. I never was crazy about the Dometic in ours. The Coleman in our 2006 Tioga Class C was great, like a home unit.

**Flybob** · 01-02-2020, 04:13 PM

Your heat vents are all near the floor while the AC vents are on the ceiling. There is no connection between them. You can also look at in the vent openings to determine the actual vent size. You will most likely find the bathroom and bedroom vents are 2" while the main room vent is 4". The further away from the furnace vents may also have the vent line constricted by a wire or support.

Kirk S · 01-03-2020, 11:21 AM

I learned about the "auto" setting quickly after our purchase thanks to this forum.
Our Dometic digital thermostat mode choices are air conditioner, heat pump, furnace, and off with high, low and auto fan settings.

When we're camping in cool enough weather we run the heat pump. With the Auto setting, if the heat pump can't satisfy the thermostat the system automatically switches to the furnace. Nice that I don't have to get out of bed to fool with it.

Comanchecreek · 01-03-2020, 11:22 AM

This would have to be the most common problem on these pages. I have to say, what is up with Dometic that they make a thermostat with such a perplexing problem for so many people? I had to figure it out, and I try to help anyone else. Good luck folks. Share your knowledge with the next guy, cause that's the only way we all figure it out. Maybe Dometic will change the thermostat in their next model release. Who Knows.

5picker · 01-03-2020, 11:30 AM

Quote:

Originally Posted by Comanchecreek

This would have to be the most common problem on these pages. I have to say, what is up with Dometic that they make a thermostat with such a perplexing problem for so many people? I had to figure it out, and I try to help anyone else. Good luck folks. Share your knowledge with the next guy, cause that's the only way we all figure it out. Maybe Dometic will change the thermostat in their next model release. Who Knows.

It isn't a problem and it's all spelled out in the manual.

It is engineered and built that way on purpose.
Heat rises and when the furnace runs, the heat from the floor goes towards the ceiling.

Dometic has given you the option to distribute that heated air via the A/C fan mounted in the ceiling. Since R/Vs are closed air systems (only draw air from inside) the A/C unit will draw the warm air at the ceiling into the A/C ducts and redistribute it throughout the R/V using the A/C fan. The compressor does not run, only the fan.

Some folks complain the air from the A/C fan creates a draft and feels cold. For those folks, they have the ability to turn it off. In bigger R/Vs (especially higher 5th wheels) there can be a HUGE temperature difference from floor level to ceiling level. Having the option to move that heated air is a good thing.

Comanchecreek · 01-03-2020, 11:36 AM

Quote:

Originally Posted by 5picker

It isn't a problem and it's all spelled out in the manual.

It is engineered and built that way on purpose.
Heat rises and when the furnace runs, the heat from the floor goes towards the ceiling.

Dometic has given you the option to distribute that heated air via the A/C fan mounted in the ceiling. Since R/Vs are closed air systems (only draw air from inside) the A/C unit will draw the warm air at the ceiling into the A/C ducts and redistribute it throughout the R/V using the A/C fan. The compressor does not run, only the fan.

I agree with what you're saying. Basically it was done that way to allow for the removal of ceiling fans in new rigs by the manufacturers. Problem is, many people don't understand the function and perceive it as a wiring problem, or some other issue. A separate switch to allow for air circulation would make much more sense to most people, in my humble opinion.

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