Furnace operation

[DonTom]

In this Class A (listed below) there are two A/C units which also have the furnace function. Both work well when the A/C is on.

The two controls, one up front and one in the rear bedroom.

I do have 50-amp service here.

The one up front can select :

1. fan low
2. fan hi
3.cool hi
4.cool low
5.cool low auto
6..cool hi auto
7. heat electric
8. heat gas
9. off.

The one in the rear bedroom can select:

1. fan low
2. fan hi
3.cool hi
4.cool low
5.cool low auto
6..cool hi auto
7. heat
8. 0ff



This is not really a problem as the furnace in front works well to warm up this entire motorhome.

Both units are "Coleman-Mach". The selectors are made by Airxcel.

The thing I do not understand is the "heat" in number 7 above. It does NOTHING when selected, no difference between "heat" and "off" that I can tell, regardless of what the front one is doing.

Is it even supposed to do anything when "heat" is selected in the rear bedroom?

I can set the temp to 99F when it is 67F in here (as set right now) and NOTHING happens when "heat" is selected. The same as when "off", from what I can tell.

-Don- Flagstaff, AZ

 

[JD Sharp]

Heat selection from rear thermostat will engage heat strip in ac unit if installed. I have same setup.

 

[DonTom]

Heat selection from rear thermostat will engage heat strip in ac unit if installed. I have same setup.

I assume that means mine is NOT installed, but can be, if I ever feel I need more heat.

-Don- Flagstaff, AZ

 

[John From Detroit]

In some RV's the rooftop A/C controls the furnace.. In others a heat strip (Electric) inside the A/C and in most.. None of the above

 

[Gary RV_Wizard]

Clearly the front control can activate the heat pump or heat strip in the front a/c (heat electric) and also the gas furnace (heat gas).

The rear control is more ambiguous, but if the rear a/c lacks a heater, typically that rear heat setting would activate the furnace. The Entegra Vision manual is vague about that, but it mentions that some coaches can control the furnace from more than one thermostat.

The rear a/c make/model info should inform whether it is a heat pump or not, and probably whether it is capable of having heat strips (many models cannot). What is the model number of the rear a/c unit?
Last, exactly what thermostat model is in the rear? Airxcel markets several different thermostats under both the Airxcel brand and the Coleman-Mach RV Comfort brand. Does it look like one of these?

 

[DonTom]

Clearly the front control can activate the heat pump or heat strip in the front a/c (heat electric) and also the gas furnace (heat gas).

The rear control is more ambiguous, but if the rear a/c lacks a heater, typically that rear heat setting would activate the furnace. The Entegra Vision manual is vague about that, but it mentions that some coaches can control the furnace from more than one thermostat.

The rear a/c make/model info should inform whether it is a heat pump or not, and probably whether it is capable of having heat strips (many models cannot). What is the model number of the rear a/c unit?

Well, I probably should consider my rear "7-heat" just another "off" position as that is all it does.

-Don- Flagstaff, AZ

 

[Gary RV_Wizard]

But maybe not all it is supposed to do.

 

[DonTom]

But maybe not all it is supposed to do.

I doubt if anything is broken. OTOH, perhaps it was never wired correctly to begin with. But if all it does is turn on the main furnace, I can live without that. But even if it does, will it be on electric or propane if the front is not already turned on?

-Don- Flagstaff, AZ

 

[Kirk]

Well, I probably should consider my rear "7-heat" just another "off" position as that is all it does.

If you don't have a rear furnace, and the rear A/C has no electric heat strips, then perhaps the builder just installed a thermostat they had in stock and didn't connect anything to that switch position. You can also check to see if the switch has anything connected to it.

 

[Ray-IN]

The exact model# of each roof-top unit, and each 'stat is required to find the service manuals online. Even that information will not tell for sure if either has an electric heat strip installed from the factory or if it is an option.
This requires someone with personal knowledge of said units and 'stats to visually confirm the exact status; like a mobile RV repair service.
One of these 120V line splitters and a clamp-on ammeter is handy to determine if anything is drawing current and how much; even if a switch position is controlling anything that draws amperage.

 

[Gary RV_Wizard]

I doubt if anything is broken. OTOH, perhaps it was never wired correctly to begin with. But if all it does is turn on the main furnace, I can live without that. But even if it does, will it be on electric or propane if the front is not already turned on?

-Don- Flagstaff, AZ

The furnace is propane and the rooftop unit would be 120vac (heat pump or heat strips). You could easily tell which is running by listening for the source of the fan noise and which ducts are supplying heat. But obviously cannot do either if nothing happens when the control is in that position.

Best guess is that the factory simply didn't wire that position, likely because the coach is not equipped with a separate rear furnace.

 

[DonTom]

The furnace is propane and the rooftop unit would be 120vac (heat pump or heat strips). You could easily tell which is running by listening for the source of the fan noise and which ducts are supplying heat. But obviously cannot do either if nothing happens when the control is in that position.

I realize the top is 120 VAC and the one that does work doesn't work all that well when it is extra cold as it is tonight here. It will get down to 21F/-6C tonight and is below freezing right now. I am now using my propane.

But I think two will work a lot better. I would rather use their 120 VAC than my propane, if two will a lot work better than one and I assume that will make the difference.

The 120 VAC unit in the rear looks exactly like the same model as the one up front. Both are "Coleman's Mach" . Looks exactly like this one (both units):

-Don- White Rock, NM

 

[DonTom]

I assume I need something like this:

-Don- White Rock, NM

 

[UTTransplant]

Assuming the 2022 RV is the one you are talking about, don’t you have a built sheet with all the components and their model numbers listed? Check it for the model number of your ACs and see how they are configured. And note most if not all heat pumps will not work below 40 degrees or so. Many thermostat systems will also not use the heat pump if the requested temperature is too far off the current indoor temperature. In our rig, if the requested temp is more than 5 degrees off, the propane furnace is turned on automatically instead of the heat pump function.

 

[Tulecreeper]

Assuming the 2022 RV is the one you are talking about, don’t you have a built sheet with all the components and their model numbers listed? Check it for the model number of your ACs and see how they are configured. And note most if not all heat pumps will not work below 40 degrees or so. Many thermostat systems will also not use the heat pump if the requested temperature is too far off the current indoor temperature. In our rig, if the requested temp is more than 5 degrees off, the propane furnace is turned on automatically instead of the heat pump function.

You must be referring to the ones on RV's. We have a heat pump for our house and it works fine down to 0 F., or below. The colder it gets, the less efficient it is and the longer it has to run to maintain the setpoint temp, but it still works. I woke up this morning to 33 degrees outside. The heater was running on and off and keeping it 72 in the house.

Now, when it gets really cold and the heat pump is taking too long to bring it up to temp I switch it to Emergency Heat, which uses heat strips, to help it along but after that I turn it back to the heat pump again.

 

[UTTransplant]

Tulecreeper, Don is talking about the rooftop heat pump in his RV. Discussions about home units won’t do this thread any good.

 

[Larry N.]

We have a heat pump for our house and it works fine down to 0 F., or below. The colder it gets, the less efficient it is and the longer it has to run to maintain the setpoint temp, but it still works.

When we had a heat pump in our house in Ohio a number of years ago, it didn't work very well much below 40*, so the installed electric strips took over. RV heat pumps are no better, perhaps a bit worse, and on our coaches with heat pumps, selecting the heat pump for heat would automatically kick in the hydronic heating system (Aqua Hot/Oasis) instead when temp was below about 40*.

Maybe they've improved the residential versions by now, but not the RV ones, as far as I know.

 

[Tulecreeper]

Tulecreeper, Don is talking about the rooftop heat pump in his RV. Discussions about home units won’t do this thread any good.

UT, I only responded to your "And note most if not all heat pumps will not work below 40 degrees or so." You didn't specify "RV"-types so I assumed you were lumping all types together.

So, explain why an RV heat pump would work any differently than a residential unit. Same technology, just a smaller size.

 

[Tulecreeper]

When we had a heat pump in our house in Ohio a number of years ago, it didn't work very well much below 40*, so the installed electric strips took over. RV heat pumps are no better, perhaps a bit worse, and on our coaches with heat pumps, selecting the heat pump for heat would automatically kick in the hydronic heating system (Aqua Hot/Oasis) instead when temp was below about 40*.

Maybe they've improved the residential versions by now, but not the RV ones, as far as I know.

Mine isn't automatic for whatever reason, so I have to manually switch to the heat strips.

 

[UTTransplant]

UT, I only responded to your "And note most if not all heat pumps will not work below 40 degrees or so." You didn't specify "RV"-types so I assumed you were lumping all types together.

So, explain why an RV heat pump would work any differently than a residential unit. Same technology, just a smaller size.

I was answering Don’s question which was about RV heat pumps. I didn’t know every reference to “heat pump” should have been prefaced with “RV“ since this is an RV forum, not a home heating forum. And maybe Gary can explain why RV heat pumps seem to be different than home heat pumps; I can’t. I just know the heat pumps in the RVs I am familiar with won’t work below temps of 40-ish.