Heat Pump and Gas Furnace

dengraham · 02-23-2009, 05:39 PM

Okay, we all know when you turn the thermastate up more than 5 degrees both the heat pump and the gas will come on until you reach the desired temperature. But, what about going the other way? That is, when the heat pump is working but the temperature drops below 35 degrees (outside) the heat pump will eventually go into "lockout" and the gas is supposed to provide the heat. However, I have never been able to get my gas to work unless I move the switch? Any ideas?

skigramp · 02-23-2009, 06:53 PM

You may have a defective thermostat ...

I suggest you give Coleman-Mach a telephone call ...

When my heat pump freezes up on cold nights the LP furnace comes on ...

jimandsue60 · 02-24-2009, 04:11 AM

Maybe yours is more efficient than most? I wish mine would work in colder temps. Mine usually shuts down at 38 degrees.

Jim

DriVer · 02-24-2009, 05:08 AM

Quote:

Originally posted by dengraham:
However, I have never been able to get my gas to work unless I move the switch? Any ideas?

dengraham, I believe I have the same issue however I will look at the forecast and flip the switch manually as required or before we go to bed.

dstinch · 02-24-2009, 05:28 AM

Our 06 journey the gas comes on after elec. shuts down. Don

skigramp · 02-24-2009, 05:31 AM

The original thermostat was not controlling my air conditioner correctly ... I put up with it for about a year ... I contacted them ... they asked for some identification numbers ... (it has been a while ago so I can't remember whether it was by email or telephone)

They sent me a new thermostat ... it was very easy to change ... a few screws ... and a phone jack like cord ...

The replacement thermostat works as it should.

DancinCampers · 02-24-2009, 07:02 AM

There are two ways the heatpump can go into a lockout mode. The first (controlled by the TSTAT) is when the HP cannot maintain the set temp. It is still operatng, but cannot raise the indoor temp up to the set point. If the set point to HP ability differential is great enough the LP should turn on to bring it up. This can happen up to three times before the HP is locked out for 2 hrs.

The second way is if the outdoor freeze thermistor opens because the coil temp is too cold. In this case the LP furnace should operate alone, HOWEVER, the TSTAT set points are changed. Following quoted from a previous post I made:

Under this condition, the gas furnace will operate. BUT, according to the manual, in this case it will come on when the indoor temp reaches 45 deg F & turn off when the indoor temp reaches 60 deg F. At this time the thermostat should be changed over to gas.

I am not sure if these set points are also used when the TSTAT puts the HP into lockout because of the first instance mentioned above.

I was confounded the first time this second condition happened to us.

AFChap · 02-24-2009, 12:28 PM

I don't know fancy explanations, but I have noted two ways our heat pump "locks out" and defaults to the LP furnace. Despite living in the motorhome fulltime and seeing these results over and over many times, I have not been able to tell what determines which result occurs.
1 - The heat pump locks/shuts down out at outside temp somewhere below 40, and the LP furnace comes on at the thermostat set temp and maintains that temp the rest of the night.
2 - The heat pump locks out/shuts down at outside temp somewhere below 40, but the LP furnace does not come on until the inside temp is more than 3 degrees below the thermostat set temp and maintains that temp the rest of the night.

Navy Flier · 02-24-2009, 12:41 PM

A point to note is that the operation between the HP and gas units has changed over the years so you need to consult the owners manual for your coach. It is not necessarily the same as the year before or after. Also, no HP, operates well when the outside temp is below 40 deg. When the outside temp is, or is going to be, below 40 you might just as well switch over to gas.

agiledog · 02-28-2009, 01:33 PM

I have read with great interest the posts on the HP. It is true that a HP is not efficient below about 40 deg.
I have a different question in regard to the gas furnace. In our coach, the thermostat is up front and it is very difficult to get the temperature where you want it in the bedroom. It is usually too hot or too cold. I would really like to have a second thermostat in the bedroom with a transfer switch. You could switch the authority from the front to the back and better control the bedroom temp. Any ideas on this? I don't think it would be hard to do if you can find the thermostat wires to the furnace in the back and route them through a SPDT switch. That way at night you use the thermostat in the bedroom to control the temp.

AFChap · 02-28-2009, 01:55 PM

agiledog

I don't see why that wouldn't work, IF you could find the right wires and put a SPDT switch in the line to switch power from one thermostat to the other. An easier solution might be to move the thermostat. Some are installed in a poor location (where they get heat from a refrigerator, light fixture, or direct air from a heat/cool vent), and can be relocated close by where they are not as drastically affected by other heat sources. You can also close or block some vents to help re-concentrate the heat from one area to another.