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lenp

Coleman Mach basement heat pump

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I am thinking of making a modification to my heat pump thermostat wiring and would like some of you knowledgeable folks to share your thoughts.

When heating, the way the system works if the thermostat set point is more than three (3) degrees higher than room temperature, it will activate BOTH the heat pump and the gas furnace.  Early in the morning it is usually significantly more than three degrees below the desired temperature of 72 resulting in both heat pump and gas furnace coming on.  In the past I have "slowly" raised the set point to avoid the gas furnace firing up but that is a pain.  

I am thinking of simply installing a switch in the thermostat wiring that sends 12 volts to the gas furnace (the white lead).  With that installed the gas furnace should NEVER come on (in the OFF position).

Only drawback I see is the thermostat has a heat pump lockout feature that disables the heat pump (if I read it correctly) if the heat pump cannot keep up with demand - gas is repeatedly called forn three times.  This should not occur (again, if I am reading the manual correctly) as long as the heat pump is able to maintain.  I don't think it will be a problem because I don't even try to run the heat pump if temperature (outside) is below 35-40 degrees (depending on humidity).

Thanks for your thoughts,

Lenp

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I have the same heat pump and hope you are successful. There are so many times when my Gas furnace starts in the morning when the heat pump has run all night. I would like to have the choice of when the gas is used vs the heat pump. 

 

Rod 

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I have installed a switch on this rv right after we purchased it. I also have a residential thermostat. I only allow the furnace to run if we are expecting freezing weather or if the DW is so cold in the morning that the fireplace won’t get her warm enough. I have also installed the chill chaser heater in the heat pump and the ac in the bedroom. It comes on whenever the heat pump comes on and adds to the heating. The one in the bedroom is all the heat we need up there. Although if your heat pump is in the basement I don’t think you can add the chill chaser. I would still do the switch for the furnace. 

Edited by Ronbo

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 I think you are going to need to change to a different thermostat to get away from the two systems operating on that thermostat. The reason that is I think is the way that thermostat operates.

 If the tempos get low enough the heat pump may not come on when it is called for.

 Now after saying that I would try your switch idea first. So then after you install the switch, maybe somehow chill the switch with cold air lowing over it to test your idea.

  Does your thermostat now connect with screws, molex connector or wire nuts.

 

 If there are just separate relays operating the two systems, then two separate thermostats would work.

 

now if you have different zones for heating and cooling that get a little different.

 

 Sure hope this is not confusing,       Vern

 

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Thanks to all who replied.

I am going to go forth and give it a try.  I cannot see any issues other than it may not like it when outside temps drop too low.  Simple fix at that time is to flip the added switch to the ON (enable gas) position.

It will be a few days before I make the change as I need to get a drill bit the correct size for the switch.  Will keep you posted.

Vern, the thermostat connects with a 3x3 and a 1x3 molex.  The 1x3 has only ground, 12vdc and GAS enable wires.  I plan to cut the gas wire and insert the switch.  The heat pump itself operates via the 3x3 with things such as inside fan high, inside fan low, compressor 1, compressor 2, 12 volts, ground, and a few others.  The heat pump control board IS NOT connected the gas furnace in any way - only the thermostat is connected via the 3x1 connector.  Only one zone is controlled by this thermostat.  The second "zone" (bedroom) is actually a second gas furnace controlled by a separate thermostat.  This second zone is rarely used.

Lenp

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Installed the switch last night and it works!  This morning ambient was 61 and set point was 72 when I turned the heat pump on this morning.  Heat pump came on and took about 40 minutes to get coach up to the set point.  Gas furnace never came on.

Mission accomplished.

Lenp

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