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-   -   Heat Pump blowing cool air? (http://www.airforums.com/forums/f427/heat-pump-blowing-cool-air-41082.html)

craftsman 04-08-2008 08:56 AM

Heat Pump blowing cool air?
 
Just checking the systems in my 07 25 Classic. I have the wall mounted control unit for my furnace and AC/ heat pump. If I set the control panel to heat pump and set the temp at say 70. it only blows cool air. I've tried temp settings below and above that with the same result. Any ideas?

TinShack 04-08-2008 09:06 AM

How long did you let it run? Mine takes about 5-10 minutes to heat up initially. After it cycles off and back on again via the thermostat, it only takes a minute or two to heat up.

CanoeStream 04-08-2008 09:14 AM

On a Classic? That should be a heat pump. My Safari SE only has the heat strip. It's fairly weak and only adds slightly warmer air. It aims to get the job done over time I guess. With the ducted breeze it's hard to tell it's any warmer but I've checked it with a thermometer. Your temps today shouldn't be too cold for the heat pump to function effectively.

DKDarrow 04-08-2008 09:18 AM

I have found that with my Dometic 15k in an 89 Excella that it takes a bit of time to start kicking out warmer air........Then downright HOT.............Let it run for 10 to 15 minutes.

As an aside, LOW voltage will definately case this timeline to lengthen.........It really likes a minimum of 110V..........

Have you checked your voltage???

TinShack 04-08-2008 09:52 AM

Quote:

Originally Posted by DKDarrow
As an aside, LOW voltage will definately case this timeline to lengthen.........It really likes a minimum of 110V..........

Have you checked your voltage???

I agree. It uses the compressor so has the same voltage requirements as the A/C.

jcanavera 04-08-2008 10:51 AM

As others have posted it takes a bit for the heat to generate. A lot to do with that is also the outside air temp. You start with a dead cold trailer in the upper 30's, it will take a while for that trailer to get to temp. Normally I'll let the furnace do the hard work in getting the trailer up to set point, then I'll switch over to heat pump. Note that once you start falling below 42 or so, the output will not be quite as hot. Normally once the heat pump starts cycling, the time it take to blow hot air is minimal.

Other things to note about the heat pumps. After a continuous run (I forgot exactly how long), the heat pump changes modes and the unit goes into cooling mode, without the fan running. This allows the external evaporator to defrost any accumulated ice on those outside coils. It's a little concerning the first time you experience this since the fan abruptly shuts down and you hear the internal workings clunk and then just the hum of the compressor running. You probably would experience this when you are attempting to bring the trailer up from a dead cold condition where the unit has to continually run.

The other issue is that in very cold humid conditions, the unit may run a lot, but not enough to trigger the defrost cycle. I had this happen in Branson one fall. I came back to the trailer only to find it in the 50's inside and the heat pump running, but only blowing out tempid air. I went outside and saw the coils were encrusted in a block of ice.

Jack

sander17 04-08-2008 11:12 AM

Check the outside temp. The heat pump in our '96 has a thermal switch which prevents it from working if the outside temp is below 45 degrees. The fan just blows cool air, so it is not obvious.

craftsman 04-08-2008 11:14 AM

Thanks. I actually let the furnace heat the interior first. The outside temp is in the low 40's today. I only let the heat pump run maybe 5 or so minutes so maybe I didn't give a chance to start warming. I'll try it again.

jcanavera 04-08-2008 12:52 PM

Quote:

Originally Posted by sander17
Check the outside temp. The heat pump in our '96 has a thermal switch which prevents it from working if the outside temp is below 45 degrees. The fan just blows cool air, so it is not obvious.

The newer units have a cut over where the heat pump is automatically cut off and the furnace takes over. In my trailer however, that cut over takes place at too low a temperature. By that point the heat pump output becomes too tempid which makes me go over and switch to furnace manually.

Jack

2wired 04-08-2008 05:10 PM

Pay attention to Jack He,s correct

DEITZ645 04-08-2008 06:01 PM

Learned The Hard Way
 
We learned the same thing the hard way in our '06. We woke up freezing one night:rolleyes:. When I heard all the noises mentioned in an earlier post I figured it was time to re-read the heat pump / AC manual again. That is when I saw that it may not work so well when the outside air temperature drops below 40 (typical man, if all else fails...read the instructions;)). The heat pump is nice to take the edge off, but nothing beats that propane furnace.

lewster 04-08-2008 06:01 PM

Quote:

Originally Posted by craftsman
Thanks. I actually let the furnace heat the interior first. The outside temp is in the low 40's today. I only let the heat pump run maybe 5 or so minutes so maybe I didn't give a chance to start warming. I'll try it again.

C,

After trying the heat pump again for a longer period of run time and it is still blowing cold air, one of two things are happening:

1: the outside ambient air is just too cool for the heat pump to extract any more heat from it to put into the trailer (as stated above)

2: your relay board on the upper unit is stuck in the closed position. I say this, because ALL Dometic heat pumps actually have the reversing valve in the 'heat pump' position as it's normal rest state. When you call for cooling from the air conditioner, the relay (K-5 IIRC) closes and reverses the valve, thus creating the proper refrigerant flow for air conditioning. If you are only getting cold air from the unit, then K-5 is stuck closed and wil not allow the reversing valve to attain it's original state.

If this is the case, you need a qualified Dometic tech to look at your unit to determine if you need a new relay board. Hope you're still under warranty!!:innocent:


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