Suburban Heat Pump

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Larry Bond

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Mar 9, 2013
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We have a Suburban (according to our manuals) heat pump with AC, gas heat & electric heat modes. The last 1.5 years we've always been able to use electric heat as long as outside air temperature (OAT) is 38+ degrees. A couple weeks ago, no more elec. heat regardless of OAT - when set to elec. heat, it defaults to gas. AC still fine, gas heat fine, but NO elec. heat. Reversing Valve? Thoughts?
 
I don't know if this is what you're seeing, but I've found that if your setpoint is way higher than the current indoor temp, my rig kicks the gas furnace in to "catch up", regardless of the outside air temp.  The heat pump function is pretty wimpy and OAT has to be pretty high (like you said, almost 40 deg) before it puts out much warm air.  It fooled me at first too, and I thought I had a bum unit, but found that eventually, I had a bit of warmth from the AC/heat pump vents as long as it was warm enough outside.  This heat pump function is not nearly as useful as I thought when I bought the rig.  We use small electric heaters on the floor.  They work better than the roof heat pump.

Gordon
 
When in heat pump mode, do the fans run but the air doesn't heat, or does the heat pump not run at all? If a reversing valve problem, the heat pump runs but you get no heat.
 
If you a "basement air" system it is likely a Coleman Mach system from Airxcel. I believe they also make roof top models. You did not say what make/model RV you have but I have never heard of a system by Suburban, but  their furnaces and water heaters are common. My Suburban Furnace is tied in with my Coleman Mach AC/heat pump system.

For the Coleman Mach thermostat, if the set point on the thermostat is 4 degrees or more higher than the inside temp then the gas furnace will be requested right away and the heat pump function locked out. Some models of the thermostat permit the AC/Heat pump fans to run at the same time as the furnace, others do not. The other constraint is that if the outside air temp is too low (ie about 40 degrees or so) then the heat pump function is aborted when the system finds it cannot raise the inside temperature quickly enough and the furnace will be called in. These heat pumps are no where near as efficient as those found in home systems.

Sound more like a dicky thermostat to me, not unusual for the Coleman Mach versions.....

 
Thank you Gentlemen. It is a Coleman Mack and not a Suburban unit. I understand the gas heating function is to kick in if the room temp is 4-5 degrees below the thermostat set temperature. But prior to losing the electric heat capability,elec heat would always kick in even when the room temp is 20 degrees or more below the set temp when we turned on the elec system. Now when I try to turn on the elect. heat, it sounds for a couple seconds like it is going to start, but then  defaults to gas. This happens even when the room and set temps are but a 2-3 degree differential. Oh, the mysteries!
Larry
 
In order for the heat pump to function you require both compressors to be functional. If, for some reason, one of the compressors will not function (as in my case currently, I have a relay that needs replacing for starting the second compressor). Another reason for a non functioning compressor might be that you are on a 30 amp site with no provision made to operate both compressors. My trailer has a second plug outside that I can connect to a secondary 20 amp supply in order to use both compressors while on a 30 amp site.

There is a very good description of the system operation in the thermostat manual and in the air conditioner manuals that can be found on the Coleman-Mach site.
 
Both compressors? Not sure what you mean, Stu.  A heat pump unit still has but one compressor - the difference is just a valve and some plumbing.

In any case, if the compressor won't run for any reason, then the controller will start the gas furnace back-up to provide heat. It sounds to me like Larry's heat pump is simply malfunctioning, maybe a bad start/run capacitor or some such.
 
Hi Gary,

The RVP 6536 series two ton units have two compressors and both are required for the heat pump function. You can get away with only the first one for the cooling function but it is not nearly as effective, as you can imagine. Only the first one can be used on a 30 amp campground connection but, as I stated, my trailer is wired so that a second 20 amp source can be connected permitting both compressors to be used. (There is a 30amp/50 amp campground selector switch only dedicated to this function and is located on the wall near all the slide switches etc.)

On my unit I can tell by listening at start-up whether both are running or not as the start up of the second one is slightly delayed and it's starting is very evident. Mine is the 6536 series but I do not know if the other series units are different.

Your suggestion is well taken, in my case the furnace will start up right away at this time  because I am " making do" by leaving my selector switch on 30amps at the moment.... the 2nd compressor will not start as the relay needs replacing, so I have, effectively, bypassed it. What you and the OP have described would take place should either compressor,  left to its own devices, fail to start. Since the OP has not told us which model of AC unit he has, my info may, or may not, apply in his case, but he did say "it sounds for a couple seconds like it is going to start, but then  defaults to gas" which made me think of the two compressor  possibility as that is exactly what mine does right now and why I electrically bypassed the 2nd unit.  Just food for thought!!!!
 
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