Furnace questions

[Terratravels]

I have just started to use the heat (Florida based) When I turn the thermostat (Dometic digital) to Furnace and adjust the temp....heat comes out of the wall vents but blows cold air out of the overhead unit.
I don't even want to use the overhead unit because it is so noisy.
In my previous AS (2008 Bambi 16) I had a separate furnace and overhead air conditioner with heat strip...which I did not use in the cold weather.
Do I have that option with this set up?

[xrvr]

Istheheatpump separate from the furnace when you select the mode? jim

[Alumaholic]

The furnace, hot-air ductwork is not connected to the overhead unit.
The overhead unit (Air conditioner and heat pump) is a separate appliance with its own compressor and and easily discernible fan.

Are you saying the AC fan is coming on when you are in "Furnace" mode?

If the answer is yes, you have a wiring problem.(Unlikely)

If the AC fan is not coming on, you are probably feeling a circulating air loop caused by the fairly powerful furnace blower. A furnace duct opening directed upward could create this illusion. (Most likely)

[Silver Goose]

The Dometic thermostat is sometimes referred to as the Comfort Control Center and the components should work as follows:

Heat Pump Mode - The A/C unit on the roof runs in heat mode and warm air comes out of the ceiling plenum, it cycles off and on when the set temperature is reached. Yes this is noisy, but doesn't use propane. When the outside temperature drops below 30, the heat pump and its blower shut down completely and the furnace comes on as needed. There are 2 reasons for this: Heat pumps become less efficient as the temperature drops and only the furnace provides warm air to the plumbing/tank area under the floor to protect in freezing temperatures.

Furnace Mode - The furnace cycles on and off as needed to maintain the set point temperature. Initially, cool air will be felt at the vents near the floor until the burner ignites. In furnace mode, the heat pump is off. The rooftop blower should not be on.

The CCC is a microprocessor and as with many of its cousins, a system reset often cures weird behavior. At the CCC, turn the switch to Off. Press and continue to hold the Mode and Zone buttons together. Turn the switch back to On. FF should be displayed, then release the 2 buttons, the FF should go away and the display will be blank except for Zone 1. Select Furnace and see if that fixes the problem. If not, or if something other than FF is displayed, make an appointment with your Airstream dealer or an authorized Dometic servicer.

This applies if your CCC looks like this one. Dometic has a newer model. I can't say if it is reset the same way.

[Terratravels]

Thanks Yankee Doodle...the reset worked fine even though I have the giant Controller II model with 11 buttons! Heat coming through the vents the AC unit is not producing any air.

[Silver Goose]

We all love to hear success stories! Thank you for letting us know what fixed it and now we know the reset process is the same for either model CCC.

[Mrs. Bale]

Does the furnace blower require 30 amps like the AC? Or can it be run off of 110?

[lewster]

Originally Posted by Mrs. Bale

Does the furnace blower require 30 amps like the AC? Or can it be run off of 110?

The furnace is strictly a 12VDC device, no AC current is used.

[aftermath]

Originally Posted by Mrs. Bale

Does the furnace blower require 30 amps like the AC? Or can it be run off of 110?

I am sure some electrician type will chime in soon with a better explanation but......a 110 service can be 30 amps or it can be 20 or even 15. Your furnace does not draw that much current so no, it does not require 30 amps.

Amperage is a measure of current flow whereas voltage is power. Your AC needs only 110 volts but it does require a lot of current, hence the 30 Amp requirement.

Someone help us here.

[aftermath]

Thanks Lew. You can run your furnace when not hooked up, of course.

[dznf0g]

Furnace blower is 12V not 120V. We are talking the furnace and not the heat pump, right? Heat pump is 120V and draws amperage very close to the Air Conditioning. 30 amp service would be required.

[Mrs. Bale]

Thanks, guys! I appreciate it.

[tdmaymac]

I had the very same furnace experience (i.e., overhead AC fan coming on in furnace mode) last night.

[tdmaymac]

Oops. Hit the send button too soon on my last post. Set in the "FURN" mode, I started out getting heat from the floor vents, but then suddenly the fan in the overhead unit came on and it wouldn't shut off in the furnace mode. I was concerned about this, as I was running my trailer on a 15 amp circuit from my house to provide heat to avoid a freeze up last night on a "yet to be winterized" AS (my first year with a Flying Cloud 27'). The compressor didn't come on (just the fan) so figured I probably wasn't over-drawing the circuit or taxing the AC unit. Anyone who knows these units well and could advise would be greatly appreciated.

Tom

[Splitrock]

An amp meter on the supply cord should read the amperage in use. At least the one I have does.

[Aage]

The old furnaces were designed to run for several minutes after the flame was extinguished in order to ensure that all exhaust gasses were expelled from the combustion chamber.

No idea if the new ones do that too. No such concept as "overhead" heating in my '74 though, so this may not be of any interest to you.

[tdmaymac]

I think I discovered why the overhead fan unit comes on when the furnace setting is selected. There are four fan positions that are available under the FURN mode and these relate not to the furnace blower but the overhead AC unit. I noticed that mine was set to LOW and the overhead fan was running, but when I changed it to AUTO, the overhead unit shut off and didn't come back on. I think this may be the trick for avoiding cold air blowing from the overhead unit when the furnace is selected. If someone has better insight into this problem, please chime in. Thanks.

Tom

[lewster]

Originally Posted by tdmaymac

I think I discovered why the overhead fan unit comes on when the furnace setting is selected. There are four fan positions that are available under the FURN mode and these relate not to the furnace blower but the overhead AC unit. I noticed that mine was set to LOW and the overhead fan was running, but when I changed it to AUTO, the overhead unit shut off and didn't come back on. I think this may be the trick for avoiding cold air blowing from the overhead unit when the furnace is selected. If someone has better insight into this problem, please chime in. Thanks.

Tom

First, ALL furnaces have an initial purge cycle and after running on heat cycle, the thermostat is satisfied, the gas valve closes to extinguish the LP flame and the blower continues to run to purge any LP from the burner area and to cool the unit after operation. All modern LP furnaces follow the same operational routine.

Tom,

When you toggle your CCC to furnace, is the fan setting still on? When you exit the cooling mode, your A/C fan should automatically go off and should not have any operational relevance to the furnace.

If you have a heat pump unit, the furnace will automatically commence operation in low ambient temperatures (around 40*F) when the heat pump can no longer produce interior heat. The furnace should automatically take over.

If you are getting the A/C blower when your CCC is set to furnace, you might have your dip switches on the relay board of the upper A/C unit set improperly, the unit might be mis-wired or you simply need to do a re-set of your CCC.

Check it out and get back with what you find.