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OIIIIIIIO 01-26-2012 04:33 PM

Heat Pump Aux. heat running too often.
Hello there, I just got our latest electric bill, and right away figured something was wrong. Im not home a whole whole lot, and have a non-programmable thermostat that is always set to 69*. Trying to figure out what changed from last winter, to this winter, (new t/stat last spring) I was home today, and made a point to keep an eye on the t/stat, and what the pump was doing, and I found the aux. heat strips are being activated at every heat request. In an effort to see if the unit was perpetually defrosting, or I had a thermostat issue, I disconnected the aux. wire from my thermostat, and in the last hour since Ive done it, my heat pump doesn't appear capable of making the 1 degree jump to the set temp, and is running constantly. So being that the aux. is running so often, im assuming this is the cause of my astronomic electric bill, and that maybe I have a charge problem? Currently the outside temp is about 35*F, and again, I have the t/stat set to 69, but can't seem to get there from 67-68* without the aux. strip.


T/Stat - Honeywell RTH3100C
Outdoor unit - Carrier Tech2000 38YH
Indoor unit - Carrier 40AQ

Pardon me if I didnt get the model numbers right... Im going off of a 23 y/o manual.

DIY_Mike 01-27-2012 10:07 PM

There are two things you can easily check.

First, check out the hole in the drywall behind your t-stat where the wiring comes through. That hole needs to be plugged with insulation, otherwise your stat could be reading temperature from inside the wall, which would be cooler than the room temp. This would be one reason why your heat pump continuously runs and calls for the heating coil. The room is warming up but the cooler air from inside the wall isn't, which is what your t-stat is reading.

Second, measure the temperature difference between the air going into the side of your condensing unit compared to the air coming out of the top of the unit. There should be close to a 20 degree difference. If it's much lower than that, it's prob a charge issue.

OIIIIIIIO 02-08-2012 06:03 AM

Well, I had someone come out and look at it (I have a home warranty that covers the heat pump) and they told me there wasn't an oz of refrigerant in it, and that the compressor was screaming hot. Told me it would require a new compressor. They got the approval, and another gentleman came to the house to install the compressor, and told me the compressor was fine, it just needed charged, and that the defrost sensor was split. Thing that gets me, is that the 1st guy said it was completely devoid of refrigerant, this guy told me he put in 3.8 lbs. and that it was fine. Well... its a nearly 9lb system... Ohh, and 8 or 9 months ago the system was fully charged.

In any event, its working now... but its a little noisier than it used to be... So... Im not quite sure what to think at this point.

Thanks for the help,

woodchuck 02-08-2012 06:10 PM

I would expect to have to replace the compressor soon. Running as hot as it did for that length of time should have done it in as far as the internal parts are concerned.

DIY_Mike 02-08-2012 07:14 PM

It's not uncommon for newer techs to misdiagnose problems, especially when it comes to testing the windings on compressors. Usually they'll use an ohmmeter to do this, which aren't really designed to give good, accurate measurements on low resistant/high HP compressors. A lot of compressors are condemned when they're still actually good. If your system seems to be working fine after having been charged then your compressor wasn't the problem. (In fact, it should have either tripped out on high temp condition due to low or zero charge, leading to intermittent operation you would have noticed, or, it would have burnt out the compressor entirely, leading to it not working at all).

It sounds to me as if you have a very small leak, either at one of the braized copper connections or (most likely and what I've commonly found during my time in the field) to be one of the schrader valves where the technician hooks up his gauges (it's the same part you would press on to let the air out of a car or bicycle tire). Eventually, the rubber that makes the seal in those schraders will dry up and crack, allowing the refrigerant to slowly leak by. At that point only the brass caps are keeping the refrigerent in the lines. If they aren't on there really good and tight, it can allow a slow enough leak for your system to take the 8 or 9 months it has been since the system was fully charged. This sort of problem won't show up in typical leak tests like a very small leak in a braized copper connection would, which could easily be missed by a less experienced tech.

If within the next year you find you have to have your system charged once again, I would say with about 95% certaintly that those little, inexpensive valves are the most likely the culprit.

OIIIIIIIO 02-09-2012 10:18 PM

Coming from the automotive world, I know its not uncommon at all to see a schrader valve or pressure switch leaking refrigerant. Especially after its been disturbed.

Im noticing its coming on every 7-8 minutes, and running for approximately 10 min. Current ambient temp is in the high 30's. Seems like it runs more often, but I honestly didn't pay THAT much attention to it before, so I could be wrong. In any event, its not running the auxiliary heat anymore, so at least my electric bill won't be through the roof again.

Thanks for all the help, I suppose all I can do now is wait, and see what happens :)


thermalmedics 02-11-2012 09:42 AM

hot compressor
If the tech ohmed out the compressor when it was hot it would show an open (IP) or internal protection that it has to stop it from burning up. Often like DIY Mike says many compressors are condemed for stuff like that. When the compressor cooled down it would operate again. The freon (and the oil that travels in it) cool the compressor so it would get hot if you have a leak and are low on gas. also in winter i see alot of heat pump's outdoor coil freezing up quickly and going into defrost often.

When you check the schrader valves look for oil in the caps or anywhere that is visible in the copper lines. Oil stains are dead giveaways to a leak spot.

Since you have a home warranty, instead of letting them dump gas in every few months and stick you with the service call fee, make them find the leak and fix it. You pay the premiums, that is their job. Also they should have a "moral" problem (read EPA)with freon venting to the atmosphere.(you can remind them of that if they balk). ive got great home warranty stories....

OIIIIIIIO 02-12-2012 06:22 PM

Well... it was nice while it lasted. We're right back at my heat pump running constantly, and using the aux. coil every 5-10 min. just to hold 68*. Without the aux. hooked up, my inside temp dropped 5* in an hour with the pump running constantly. Guess Im out of refrigerant again... yay. The guy that was here last made me feel like an idiot, because I didnt understand how the system could lose 8+ lbs of refrigerant in 9 months and be leak free. Told me that its not uncommon to see a system lose a lb. or so a year. (Which, with an older system like mine, I can see losing a little being the seals and what not are old.) But then he told me he checked the whole system over and there weren't any leaks. Which.. like I said, was full 9 months ago.

So, basically, the system was full 9 months ago the last time it was checked. 3 weeks ago, it was empty. The first guy put 8lbs. in, and it was full. Then, 2 weeks ago, it was just low, and the guy added 3.8 lbs. and I was a jerk for thinking there was a leak. Now, week three, its apparently low again.

Could it be... a leak!?

Atleast winter is nearly in the bag, just soon enough for my A/c not to work.

Do you guys use a UV dye in a home system like we do with cars?

thermalmedics 02-12-2012 09:08 PM

dyes work
yes there is some dye type stuff you can dump in and look for. If it is leaking that much than it shouldnt take anyone too long to find it out. Dump whats left of the charge and fill it with nitrogen and you'll probably hear it hiss from the can.

MAJOR TIP re home warranties

I did some work for some as a sub and it is a sad biz, but.... you should be able to call back within 30 days with the same complaint and the original company should come out- with no service charge.

Hold em to find and repair the leak and dont let them give you any pre-existing condition bull or other excuse. I came in after one denied a claim because the tech said someone used a special glue (!) on it....
That one was just too easy..

good luck and let everyone know how it turns out

DIY_Mike 02-15-2012 07:53 AM

I agree, this should be a pretty easy leak to find if you're getting that much of a freon loss. You wouldn't need to use a dye to find it. It could still be the shrader valves. Once a tech hooks his gauge manifold up, he's sealing that leak up and wont be able to detect it using any leak test technique. Just dab some soapy water over the caps to rule it out. Takes 2 minutes to do without tampering with anything.

Rule that out first. If that's not it, I would want my system to be evacuated and a vacuum test done at this point. There is obviously a leak somewhere and the system is going to have to be evacuated anyway in order to fix it.

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