DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   HVAC (
-   -   How to test apartment Heat Pump (

tbrubes 02-03-2009 10:52 PM

How to test apartment Heat Pump
Hi all,

I have an ongoing battle with my apartment complex over whether my heat pump works. The heat pump is new, but the air handler and thermostat are old. It's not been wildly cold out -- between 30 and 50 deg F.

The thermostat has two mercury bulbs for switches. My understanding is that one bulb controls the outside Heat Pump and the other bulb, set at a very slight angle to the first, control the Auxiliary heating coils, so that typically only the heat pump runs, but when it gets really cold, both mercury switches are on and both heat sources run. Is this correct?

My problem is that the maintenance staff have adjusted the bulbs to be perectly parallel, so that they are always either both on or both off. My theory is that this is masking the fact that the heat pump doesn't really work because I am now always using electric aux heat, whether it is needed or not.

If I separate the bulbs myself, and just run the heat pump, the air feels cold. Also, both copper lines to the outside heat pump feel cold. Is this a good test? Oddly, if I let the aux heat bulb on, one of the copper lines suddenly heats up, which surprised me because I thought this was activating the aux heat and shouldn't affect the heat pump. Does this make sense?

Can anyone suggest a good test to prove whether or not the actual heat pump is working, regardless of what the aux heat coils are doing?

Thanks for any insight


kennzz05 02-04-2009 12:12 AM

\sounds like theres some wireing screwed upyou are right in assuming the first bulb is for the heat pump and the second for the elec heat. the line should be warm/hot when the first bulb is calling for heat and not only when both are calling. somebody dosent know how to wire the tstat correctly. so that should be your test when the first bulb is made it should be heatpump only. the line will be warm whenever the heatpump is running(unless its in a defrost cycle, but that dosent typically last long) i didnt know you could make the two bulbs react at the same temp without maybe bending the spring guess i just never would have thought to do that to mask a problem

beenthere 02-04-2009 04:40 AM

Miswired somewhere.

Your going to get a big electric bill.

tbrubes 02-04-2009 05:41 AM

Thanks for confirming my understanding of how the tstat works.

Bending the spring is exactly what he did.

It's still odd to me that the heat pump can be running but not producing heat, and then very suddenly start producing heat when the aux comes on (again, measuring this by feeling the line, not the air in the house). Does that still sound like wiring? What is the heat pump doing when it is spinning away waiting for the aux heat? Something is wired right to at least get the fan turning up until that point, and I wouldn't have thought control of the compressor would be separate...

PS beenthere, I grew up in Lancaster, PA. Guess the Internet isnt such a big place after all:)

dac122 02-04-2009 07:45 AM

My gut also says it sounds like something is wired backwards. But to be sure, can you post the make/model thermostat, and wire colors to terminal mappings?

What happens if you put the tstat into em/aux heat only mode? Do your copper lines get warm then?

Bending the springs is an unprofessional approach to fixing the problem. Tell your maintenance staff we give dope slaps for that. :)

tbrubes 02-04-2009 12:40 PM

Heatpump is a Duroguard DPBC-0245A
Thermostat is a LR11746 Class 2

If I put it into EM heat only, nothing happens outside... the copper lines stay cold.

If I put it on Heat Pump only (by looking at the mercury switches), the heat pump fan turns but the copper lines stay cold.

If I let aux heat come on while heat pump is on, the outside unit shakes once and suddenly one copper line gets hot.

Not sure what to make of the wiring/terminals. They seem to mostly just match their respective colors:

Y - Yellow
G - Green
R - Red
O - Orange
W2 - White
E - Brown
C - Blue

Blue and White go to the aux heat mercury bulb. Blue also is soldered onto some resistor at the top of the tstat.

Brown, white, and black go to the other mercury bulb. And black goes into some resistor....

beenthere 02-04-2009 02:11 PM

Isn't Duroguard, an off brand name of Rheem.

Without knowing what the wires are connected to at the air handler, and outdoor unit, can't tell you if what wires are wrong.

dac122 02-04-2009 03:05 PM

The wire mapping at the tstat seems reasonable. The next step is to follow them to the air handler and HP.

All times are GMT -5. The time now is 08:18 AM.