Atwood Heat Pump

The question is, did the furnace operate correctly - that is, did the furnace run up to a temperature set on a thermostat somewhere? According to how mine work, the Furnace switch shuts the Atwood off and lets the furnace control operate the furnace by locking the relay in the Atwood unit on. That is why mine headed for the super hot realm of 90 degrees or better because nothing was telling it that the temperature was reached. But the Atwood will do that with the thermostat in heat mode, but the furnace button off, that is, it will operate it at the set point temp.

I have just been outside in my RV. I checked the temp outside was near 40 degrees. I turned on the rear unit alone and checked the inside air temp to be 50 degrees - I have a small space heater to keep things from freezing.

When I turned on the a/c it was set on Auto fan and heat - Furnace off. It started the compressor immediately and after running the compressor for 2.5 minutes it turned on the fan at low speed - by 5 min it was running at medium. The temp of the output air was 66 when the fan started and went up to 89 by five minutes. I checked it periodically as it ran and the temp was at 105 when the compressor shut down. The room temp was still about 66. The kicker was that the fan ran for awhile after the compressor shut off, but then slowed to med and low and off. Then after about 30 secs it turned the fan on for a 5 sec run then off and the compressor started again.

I measured the temp of the output in the main cabin vents, too. Even though the
front a/c heat pump was not running, the temp in those vents was the same as in the bedroom vents each time, but the main cabin did not make it to 75 (the set point temp).

As the unit ran on, the temp at the thermostat gradually rose to 74 for a setting of 75 and the wall temp got to near 70 degrees. So you can tell we have a pretty good heat leakdown rate in the bedroom. The main cabin did not get above 68 until after the bedroom was at temp for awhile.

I am planning to add the front a/c, but I have not turned on the propane so it won't start. The fan will start but the furnace won't run without fuel.

The furnace worked when I got it back when I pushed the furnace button.....

You are correct, the Atwood is an excellent choice. The thing is designed to operate based on a different premise than most manufacturers use. But your experience is not a fault of the Atwood design, perhaps it is a faulty unit, but I suspect a more faulty installation.

PS I am not a spokesman for Atwood.

The old installation used Dometic, but how large is the coach? How is the air taken in and let out - I assume ducts. What did the ducts look like that were taken out - are you sure that the unit has the separator in place to keep the intake and output apart? Only one unit? What is it a fifth wheel?
How did he run the wire for the thermostat - through the ducts on the surface or something else? Or did he splice the old into the new? If he did, check the continuity of the wires. Since the furnace doesn't work, that could be bad and not show up as obvious.

jdubya wrote:
There is no wiring diagram of which I am aware either, but the unit does not use the relays as the Colemans do. The diagram on the inside of the cover is not much more detailed.

Have you tried running it with the two vent doors open?If it is short circuiting, that should make it run longer.

It would help to know more about your installation. What was in there and what came out - how you checked it for fit and function etc before deciding to install it. What is the unit you have installed it in, etc. Since the installer did this for you, he should be able to tell you what he did and why he thinks it is working as good as it should.


Like I said, mine works like a champ except for the idiosyncrasies that I mentioned and I had to mess with Intellitec interface as well. Dometic is clearly trying to kill this unit - Atwood had signed an agreement with the designer of the Cormorant and Dometic is being forced to sell it until they can prove that it is not a good product. Unfortunately, their own product (the small one) is pretty poor also and has lots of problems.

I replaced a 7 year old Dometic 15,000 A/C that developed a loud rattle.....At the time the Atwood seemed to be the logical replacement based solely on their advertisements.....false advertisements at that.....As I live in central Florida winter temps are not that harsh so a heat pump seemed the logical replacement...

There is no wiring diagram of which I am aware either, but the unit does not use the relays as the Colemans do. The diagram on the inside of the cover is not much more detailed.

Have you tried running it with the two vent doors open?If it is short circuiting, that should make it run longer.

It would help to know more about your installation. What was in there and what came out - how you checked it for fit and function etc before deciding to install it. What is the unit you have installed it in, etc. Since the installer did this for you, he should be able to tell you what he did and why he thinks it is working as good as it should.


Like I said, mine works like a champ except for the idiosyncrasies that I mentioned and I had to mess with Intellitec interface as well. Dometic is clearly trying to kill this unit - Atwood had signed an agreement with the designer of the Cormorant and Dometic is being forced to sell it until they can prove that it is not a good product. Unfortunately, their own product (the small one) is pretty poor also and has lots of problems.

Update: I looked at the board (quite cursorily) and I believe that there would be very little value-add to have a more complete diagram. There is a diagram similar to the one in the installation manual on the unit (inside - you have to take off the roof-top cover to get at the electronics, it is not available from the inside of the coach). The only other diagram information would be to detail the thermostat, which you know they aren't going to do. I suspect that they use a microprocessor on the thermostat to interpret the inputs from the thermistors (four) and determine the situation for the operation based on that information.

Bob Vaughn, I feel your pain - it should operate. The indication is that the heat pump is short circuiting on the air flow - by that I mean there is a leak between the output and the input so that the hot air goes back into the unit to soon. According to the installation guide, that can cause it to turn off too soon. If the unit will air condition properly, it might be that the reversing unit is not functioning, but that usually would show as a fault.

There could be a faulty unit - I can tell you that at 40 degrees, the thing puts out enough to heat my 35 ft all by itself - and the temperature at the outlet is upwards of 100 degrees.

If your furnace does not operate, press the furnace switch once. If it doesn't come on and the setting of the thermostat is above that of the room (determined by pressing 'sleep' and holding it for 5 secs) then the thing is not installed properly in all probability.

jdubya wrote:
to Bob Vaughn and imgoing4it: The furnace will run on its own. All that should have been done is wire the furnace thermostat's relay in series with the thermostat wire from the furnace plug of the Atwood. If you press 'Furnace', the Atwood thermostat turns on the furnace relay in the Atwood a/c and turns the heat pump off, allowing the power to the furnace of the RV. However, then you do not have a thermostat to operate the furnace unless you have one from the original installation.

The better way is to allow the Atwood to run the furnace with 'Furnace' off. This allows the atwood thermostat to operate the furnace using the atwood thermistor and to run the heat pump when it can.

I had quite a time to figure out how the Intellitec controller was able to operate the furnace. Finally I discovered that I had misread the instructions which said how the Atwood works in heat mode, plus I had grabbed the wrong wires. The 12 vdc power goes to the furnace and then out to the heat pump through its relay and/or the relay from the furnace thermostat if you have a separate one, then back to the furnace where it goes to ground. Both of those wires are blue, but the intermediate wires between the systems are striped, etc.

Does that help any??

I contacted Dometic/Atwood and asked if there was a wiring diagram available not the block diagram on page 20 and they said NO....not available......I call BS on that response....there has to be a wiring schematic to assist installers and repair tech's....I have concluded that they do not have any subject matter experts in their customer service dept.....

imgoin4it wrote:
I garantee if the thermostat does not at least start and run the furnace, there is something wrong with a sensor, the thermostat or the installer missed something. Mine seems to control the temperature while on the furnace, however I have to play with it to find the comfortable temp. Can't trust to set it and get it. I'm still working with people to get it operating like it should. The factory guy told me how it is designed to work and mine does exactly as he said except it will not heat my coach or get it too the set temperature with the heat pump. The outlet temp is hot enough, but it will not run long enough to get to set trmp. Not sure it will ever happen and may have to junk it and eat the cost.

It was 48 this morning when we got up so I turned on the heat pump and it works the same as before even tho the installer had it for 3 days working on it and said it was as fixed as it was going to be....and as before the outlet temp was just barely warm and only ran for a couple of minutes........I am totally disappointed in this purchase....

to Bob Vaughn and imgoing4it: The furnace will run on its own. All that should have been done is wire the furnace thermostat's relay in series with the thermostat wire from the furnace plug of the Atwood. If you press 'Furnace', the Atwood thermostat turns on the furnace relay in the Atwood a/c and turns the heat pump off, allowing the power to the furnace of the RV. However, then you do not have a thermostat to operate the furnace unless you have one from the original installation.

The better way is to allow the Atwood to run the furnace with 'Furnace' off. This allows the atwood thermostat to operate the furnace using the atwood thermistor and to run the heat pump when it can.

I had quite a time to figure out how the Intellitec controller was able to operate the furnace. Finally I discovered that I had misread the instructions which said how the Atwood works in heat mode, plus I had grabbed the wrong wires. The 12 vdc power goes to the furnace and then out to the heat pump through its relay and/or the relay from the furnace thermostat if you have a separate one, then back to the furnace where it goes to ground. Both of those wires are blue, but the intermediate wires between the systems are striped, etc.

Does that help any??

to imgoing4it: I think that you are basically correct in your assessment of the method the Atwood uses. Atwood went to Cormorand and got them to modify the system for the US market and then was bought out by Dometic. Dometic is not really interested in fixing problems with the Atwood because they thought they had a winner in their other pile of offal that they were selling. But they have had so much trouble with it that it looks like everything is going to backfire. This Atwood is quiet and can really put out the heat. If you are having trouble with pulling enough heat out of it, the chances are there is something wrong with the installation.

Look for places where the ducts are blocked or things like that. Try opening the system so that it doesn't use the ducts to see if it does better. If it does, something has gone wrong with the ducts in your coach.