Hooking up the thermostat for a Coleman mach 8 with Heat Pump

[Seangie]

I decided to take February off and get some work done on the bus.  So we are staying an extra month here in San Antonio -

Anyways - I'll be posting some of the stuff I am working on over the next few weeks.  Enjoy -

I got this Coleman Mach 8 (model number 47074-879 which is now discontinued and there is a newer model to replace it) for a steal from Bontragers on the Indiana/Michigan border.  The guy that sold it to me told me that I needed a few specific parts (a specific ceiling assembly, control unit and thermostat) to make it work correctly.  He also told me it wouldn't work in a non-ducted application.  Well I did my homework and found out that the free non-ducted ceiling assembly that comes with all the roof AC units would work with this unit and I just wouldn't get heat No worries there since it was August. Got it home, hooked it up and had AC.  Yay.

Then comes winter.  We have been using a small box heater and oil filled radiator which have done us well so far but of course my curiosity got the best of me and I figured since I have a heat pump in the ceiling we might as well make sure it works.  Instead of just getting the regular ceiling assembly with the heat pump controls I went for the plain plastic cover, control box and a wall mounted thermostat to make it work.  I have heard from many that you cannot use a thermostat for a roof air in a non-ducted application which I found out is not true.  At least in the case of Coleman Mach AC units.

So after looking up the parts on the Airexcel website www.rvcomfort.com/rvp I got to installing.  It was very simple and it works great.

Here are some videos for your enjoyment -
Installing thermostat for Coleman's Mach AC system

Installing thermostat for a Coleman Mach AC(part2)

Now - As far as the performance -

This heat pump does fairly well.  Keep in mind that it is a heat pump and will not get up to 150-180 degrees like electric or gas heat but it does get up to about 110 degrees depending on how cold it is outside.  Since most of you are smarter than me I'll spare you the ins and outs of a heat pump.  Wifey doesn't care for the fan blowing and the noise it makes and I would say its like a warm breeze on a summers day.

We had it running all last night and it got down to about 28 degrees outside.  The heat pump did keep the bus at about 70 degrees turning on and off every 15 -20 minutes or so and running for about 10-15 minutes.  It puts out about 85-90 degree air when it gets below freezing.  If it gets too cold the heat pump will turn itself off and the thermostat has a control wire to kick on auxillary heat and you can hook that wire up to whatever aux heating system you want to use that will turn on with a 12v signal. 
When it gets above freezing the heat pump will easily kick on some 100+ degree heat.  I measured 85-90 degree heat in 28 degree temps, 90-100 degree heat when in 32-36 degree temps and 100 - 110 degree heat in 36+ degree weather.  Keep in mind that the 28 degrees was with no rain/snow/wind and that a few days ago when it was 28 degrees and sleeting the heat pump was blowing cold air (around 65 degrees) and eventually stopped and turned on the aux heat.

This is a great system for those of us in mild temps for most of the year.  Our single 15k unit kept the whole bus warm (we have a very open floorplan).  It is very nice having the thermostat as you dont need to have the roof airs fan running the whole time as you do when using the manual controls.  The thermostat automatically kicks the fan on and off with the heat/AC. Another nice thing is that it gets rid of the moisture in the bus. The only downfall to this unit is that the Heat feature only has high fan where as the AC has a low and high fan feature.  I think we would rather have the low fan running with the heat pump.  Im going to see if I can switch the control wires and make that happen after a call to the airexcel guys (who have been super helpful by the way.)

There is also an auxillary heat strip that you can buy and install into this unit which would probably boost up the heat at the cooler temperatures and keep the unit from freezing up as quickly when it started to get below 32 degrees outside.  I have not purchased this yet and will probably wait until next year to do so as winter in San Antonio should pretty much be over by now

If you have the Coleman aux heating strip lying around in your garage and want to get rid of it...

-Sean

[will4104]

According to my coleman literature, the auxiliary heat is intended to take the chill out of the indoor air when the air is a few degrees too cool for comfort. When properly sized, the heat is an effective "chill chaser". It is not a substitute for a furnace. I don't have your particular model so, I would check into it. Mine, at least, seem to hardly heat at all. I can feel luke warm air, seems a hair dryer would put out more heat...

Will

[Seangie]

According to my coleman literature, the auxiliary heat is intended to take the chill out of the indoor air when the air is a few degrees too cool for comfort. When properly sized, the heat is an effective "chill chaser". It is not a substitute for a furnace. I don't have your particular model so, I would check into it. Mine, at least, seem to hardly heat at all. I can feel luke warm air, seems a hair dryer would put out more heat...

Will

Will -  Ive looked at the auxiliary heating attachments for these units and they put out very little heat (5k btus is whats llisted) for the amount of air that is flowing through them.  But - in the manual for the mach 8 heat pump they show the placement of the aux heater in front of the evaporator in the return air.  My thinking is that the aux heating in this application is not heating the bus but rather keeping the unit from freezing up and supplying a few extra degrees of heat when the heat pump is running.  Therefore allowing the heat pump to run better in colder temps.

I'm not an HVAC guy so I am only guessing here.  But would be interesting to see if it made that much of a difference.

-Sean

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

[will4104]

I'm by no means any HVAC guy either, just happened to have been going thru my own heating and cooling systems on the bus and remembered seeing that in the paperwork on my AC's. Also, mine aren't mach 8's either. Just trying to help. Hopefully, someone with more experience will chime in?

Will 

[Seangie]

Will - what model of roof airs do you have and what are you using for heat?

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

[will4104]

Sean, I have two coleman mach III with heat strips and two suburban dynatrail furnaces, living in Fla at the moment so, both work very well.

Will