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heat pump blows cold air during defrost

Posted by xracer (My Page) on
Tue, Nov 16, 10 at 22:51

i have a 3 year old goodman heat pump. the first 2 heating seasons it worked fine. this year i am getting cold air under defrost conditions. the heat strips are not kicking in while defrosting. under heat conditions the strips kick in as needed. anybody have experience with a problem like this? possible bad defrost circuit board?


Follow-Up Postings:

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RE: heat pump blows cold air during defrost

I have the same problem. Same brand but mine is 4 years old but has been doing this all last year. Had the tech out about 3 different times and he changed a board but made no difference. He keeps telling me it was this way all the time and I never noticed it. I know better than that! Used to it would go into strip heat during defrost because you could tell it was warmer and during this time my blower speeds up(variable). Now the blower speeds up during the defrost but the air is cold and the room temp even drops 2-3 degrees during defrost. Then when defrost is over the strip heat clicks in and the blower continues on high until it gets heat back up, then clicks back to heat pump. I can't figure out why the tech cant get this fixed. It is murder on the power bill and uncomfortable also. Post back and let me know what you find out. Another thing, when it first goes into the defrost if you look at the power meter it really speeds up like the strip heat is on although the air is cold coming out. Then after the defrost the thermostat clicks again and that is when you can feel heat starting to come out again.


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RE: heat pump blows cold air during defrost

What happens if you bump the thermostat up a degree or two while in defrost mode?


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RE: heat pump blows cold air during defrost

I haven't tried that. I will and see what happens.


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RE: heat pump blows cold air during defrost

Techs; Can you give us your thoughts/theory on this please?.


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RE: heat pump blows cold air during defrost

See if the backup heat coils (or whatever backup heat you have) is working.

The backup heat is cycled on when a heat pump enters defrost mode since it is actually in AC mode to heat up the condenser outside.


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RE: heat pump blows cold air during defrost

Sparky...Don't let the Irisman handle throw you off. I have a masters license and have been in this business 35 years. If it helps, I have several masters degrees also, one I just attained. I'm trying to help you but surely since I am not at your location, there are a few things you can do to help narrow some symptoms down and the feedback will get you closer to what the problem is and not what it "Might" be. You never came back with what happens when you bump the thermostat up 1 or 2 degrees. If you hear a click and no heat, the problem will be an entirely different reason than if you do get heat. I have an idea of what is wrong but unless I know the symptoms, it wouldn't do either of us any good to say that is what is wrong.


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RE: heat pump blows cold air during defrost

I am not trying to not cooperate BUT the weather hear has been warm enough that I haven't needed it or it has run very little during the night. It is 64 degrees now and it is 12:40 AM. Supposed to turn colder during the weekend so I will see then. I know when it clicks (if I hear this, but I have) to enter defrost I am not sure if the symbol is blinking on the thermostat for Aux heat then, but after the defrost and the house is cooler the thermostat clicks again and then the symbol for Aux is blinking and it starts warming up. It worked so well for 2 years, then all of a sudden started this. I will post back as soon as I have more details.
Thanks!


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RE: heat pump blows cold air during defrost

I'll try to explain without a lot of jargon or text book quotes so hopefully, you'll get an understanding. There could be any number of things that "might" be causing the problem. When the unit kicks in to defrost mode, it is generally controlled by time and temperature. There are several components that control the cycle. On Goodman and Janitrol units especially (some others too), the contacts on the defrost timer that send signals back to the heaters are exposed, i.e. not encased in a plastic cover. More times than not, I have found insect parts stuck between various contacts, stopping the points from making contact and sending the signal back to the heater relay. Most times it's those little white silky spider webs (or whatever the bug is) that get caught in there. I've also seen these get rusted and corroded due to moisture as well as, badly burned due to use, power surges and low voltage situations.
When the unit goes into the defrost mode and you get a heavy, strong sounding click at the heat strips but no heat, that means the relay closed but the first stage aux heaters don't come on. If you bump the thermostat up a degree or 2 and hear a heavy click down at the heating unit and you get heat, the second stage aux. heaters kicked in. If the heater didn't come on, either the relay or the heat strip are defective. Again, many times the relay has dust or something else that keeps the points from making contact.

My suspicion is, the first stage heat strips are not kicking in. I suspect either the defrost timer contacts or, the relay that signals back to the heater needs cleaning or replacement. A good Tech will trace down the problem instead of replacing parts until he hits the culprit.

To fix the problem is very simple but, unless you are very knowledgeable with electricity, it might not be a DIY job. It would be easy enough to walk anyone through the process but there are dangers. There are 240 and 12/24 volt circuits back there that must be observed or turned completely off to prevent personal injury or damage to unit components.

Again, without being there to touch, feel, look and listen (original set of refrigeration tools needed) I can only give a best guess. I could very well be way off base. But experience would have me investigate the areas I mentioned.


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RE: heat pump blows cold air during defrost

Had colder weather lately so I have paid more attention to this HP.
When the hp goes into defrost,the therm. clicks but the Aux heat does not come on. It has the little symbol but it doesn't flash until defrost cycle is over,then therm. clicks again and Aux symbol starts blinking and it get warmer. Also during the defrost period the fan kicks in to a higher speed and the air is cold(feels almost like a/c) and it cools the rooms off more. Then when the Aux heat is running the fan is still running faster but the air is warmer. Also to answer your question about bumping it up--When it went into defrost I bumped the temp up 2 degrees and the therm clicked and the Aux heat symbol started blinking but it didn't put out any warm air until the defrost cycle was over and then it started getting warmer.

Another thing I noticed, sometimes it will kick on and the hp will run for 5-6 min then Aux heat will click on and the blower speeds up and this runs for 2-3 min and it is heating,then Aux kicks off and fan continues to blow fast for a min or so then it kicks off. I have noticed it doing this several times, then other times it runs and kicks off just using only hp for heat--and this is the same night. The outside temp was 31-33 and the therm was set to 68. I did keep up with the times(minutes) also. I would appreciate your input and any ideas you have.

Thanks


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RE: heat pump blows cold air during defrost

Xracer--Did you find out what the problem was with your heat pump?


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RE: heat pump blows cold air during defrost

not really. mine started working again almost. it works correctly about 5 out of 6 times then once in a while it blows cold air. i can live with that. i figure when/if it ever stops working totally it will be easier to figure out what is wrong.
after the advice given here i watched mine work. my aux heat light in the thermostat does come on when its blowing cold air.


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RE: heat pump blows cold air during defrost

Had my service tech out today. He first said it was the board, then he went outside to the unit and put it into defrost. Said it was calling for heat. Now he says that he will talk to the owner of the company that put this in, but he thinks they need to add another 5k strip heat. I have 10k now. I told him I didnt understand that since it worked great for 2 years. He said he would get back with me about installing the extra strip. I still dont think that is the problem, if so it wouldnt have worked right from the start. I told him this, and he just didnt answer.


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RE: heat pump blows cold air during defrost

The not working now but used to part is what doesn't make sense to just add another 5k strip. My system when new had a 15k strip that was staged 30/70 with the 30% being my first stage and defrost. In defrost the air was still cooler than room temp so I had to swap wires on the stat so I now run 70% for my first stage or defrost and have 30 in reserve for my second.

This is not the 'most efficient' some think but the cold blast of air makes everyone feel cold and eventually the stat gets turned up.


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RE: heat pump blows cold air during defrost

I asked him about the defrost, when that starts shouldn't the strip heat symbol flash then. He said No. It doesn't flash now, it waits till it is finished defrosting, then clicks again and the symbol flashes BUT I think when it was all running right , it flashed at the beginning of the defrost. I wonder if part of it is the thermostat. He went in there before(last time he was here) and "changed" something in the programming which I know nothing about. I dont even know how to get in to the programming part. Never had any instructions for it. It is just a digital White/Rodgers.


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RE: heat pump blows cold air during defrost

From what you have described until now, the Tech. always leans toward replacing a board. As you described early on, board replacement never fixed the problem. Sure, I've installed brand new components that didn't work when I put them in. I've had some that I watched fail just before I closed up the unit when I thought I was done. But my take is, the problem should be isolated so one is sure the part being replaced, needs replacement rather than a constant trial and error approach. However, if all this is being done with no cost to you other than the inconvenience, it is to their advantage to find the problem. If you are paying for this, insist they find the problem and make sure you aren't paying for a long string of parts being replaced and associated labor until they hit the right one. Sometimes replacing suspect parts can keep the labor costs down (parts are relatively cheap) but when the right part gets hit on, you shouldn't be expected to pay for the whole string of parts replaced. What makes that statement sketchy is there are times when there is a compound problem.

If you have a good, moderate responding thermometer, how about letting us know what the air temperature coming from the outlet closest to the unit is, when in the defrost mode. Also let us know what the outdoor temperature is at the same time. Please understand this isn't a drill just to give you something to do. As any professional knows, the term "feels cooler than last year" is very subjective. I know you are aware of what "cold" air and "cool" air are and what your unit is capable of. It is a great help to know what the temp is. It could be that in the past, the second stage strips were engaging and they aren't now. That's why wanting to know what bumping the thermostat up 2 degrees might have done. Bumping it up a few more degrees (maybe 4 or 6 degrees)while in defrost mode might help with a long distance opinion. Right now in my mind I am teeter tottering between the thermostat or a malfunctioning control while in defrost mode. Not being there to actually trouble shoot means I can only give my best guess. The thermostat could have a malfunction or it could be a simple programing/setting issue or, the first stage heater isn't doing the job.


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RE: heat pump blows cold air during defrost

Here is a little more info: No so far I have not had to pay anything.Glad of that.

I used a digital kitchen thermometer so I am not sure how accurate it is.
Today outside temp was 38-39 and HP temp air was 89-90 degrees.

When I caught it in defrost it was 32degrees outside and the air from the vent was 69degrees. After the defrost the Aux heat kicked in and it got to 101 degrees.
The tech measured the air temp yesterday with the Aux on and he said it was 109?

I will try bumping it up 4-6 degrees the next defrost I catch.

What should the air temp be from the vents normally?

Thanks for the help.


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RE: heat pump blows cold air during defrost

The kitchen thermometer even if not accurate, gives a good idea what is not/is happening. The 69 degrees indicates you are basically just recirculating air with minimal supplemental heat during defrost. It's quite possible the first stage heat strip is shorted in such a way it is only partially working. If you weren't getting any supplemental heat, I would expect to see the output temperature to be in the upper 40's or lower 50's since it would be in the air conditioning mode. Of course this would be determined by at what point in the cycle you took the temperatures.

The temp in just the heat pump mode might be anywhere from the upper 90's to the low 100's depending on outside temperature. That's why folks used to gas or oil find those temps uncomfortable.

If you catch the unit on defrost and bump the thermostat up 4-6 degrees and heat strips come on, you've most likely narrowed the problem to a faulty thermostat or first stage heat strip or control. Although I have run into bad heat strips and relays, I run into faulty electronic thermostats, especially the more inexpensive ones, most often. Countryboymo pointed into that direction with his experiences. I wouldn't suggest adding more strips, I would just get the ones that are there working as they did before you had the problem.


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RE: heat pump blows cold air during defrost

Also want to add that you can probably find your stat owners manual at this website:

Here is a link that might be useful: Stat home page


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RE: heat pump blows cold air during defrost

I bumped the therm.up 6 degrees during the defrost but it still did the same thing. Air coming from vent was 61 degrees until defrost was over and hp kicked back in, then aux started working and helped heat it back up. That 60 degree air gets cool when it is blowing out especially since the blower kicks into high during this time.


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RE: heat pump blows cold air during defrost

From a long distance perspective, I would look at the defrost timer to see if it is sending a signal back through the circuit to activate the heat relay.


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RE: heat pump blows cold air during defrost

I've noticed the same issue with our Carrier HP. When defrost kicks on, the air blows cool for a minute or two until the deforst cycle is over. We do have the HP set to the low cost option/setting (jumper in panel), so maybe this is the issue. It doesn't really bother me, because it only lasts a short time. It doesn't lower our home temperature, which is set to 70 day/68 night in winter with the fan on recirculate mode.

The aux heat strips very rarely comes on, but they do work. I left the heat off by accident this fall for a few days when out of town, and the house was at 55 when I got back. Turned on the HP and the aux kicked in pretty quickly. Heat pumps seem to work best by maintaining a constant temp., as opposed to the on/off blow hot air nature of traditional natural gas furnaces.

The only thing I've done to it over the years is clean it and add bushings cut from sheet rubber to the plastic grill attachment points and add rubber bushings to some panel joints to keep it quiet like when new. Some of my neighbors' heat pumps make quite a racket.

We had the HP installed in '01. It blows air gently at body temperature and it works down to 0 degree F (and maybe below) in heat pump mode. The other morning it was 2 degrees F and the HP was quietly working in HP mode providing warm air at the registers. This is really amazing technology! I would never have come up with the idea of pulling heat from cold air.

Our home is app. 2200 sf, a split level, and our highest total montly electric bill is around $180 in the coldest winter month. I just replaced the last 3 original aluminun windows this fall, and the attic is very well insultated. Even though our electric utility is a self-serving, unregulated monopoly and has the highest rates in our state, we keep striving to LOWER energy usage and costs. The efficient heat pump really helps!


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RE: heat pump blows cold air during defrost

I gave the wiring of the thermostat some thought at first but discounted it because everything was previously working satisfactorily until this year.

Yes, the concept of the heat pump is quite simple and has been around for some time and has greatly improved. It's based on the fact that any temperature above -459 degrees (absolute zero) has molecular movement and therefore heat. As time goes on I expect to see heat removal and transfer to become even more efficient at lower temperatures. To some extent, it is done in the aerospace industry but not quite cost effective for general application.

Sparky and xracer, I hope you guys get back to us when the problem has actually been isolated. It sure will be a big help to others and I'd surely like to know.


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RE: heat pump blows cold air during defrost

Sparky...ever get it figured out? I've had exact same problem for 3 years


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RE: heat pump blows cold air during defrost

I have the same problem, only mine has been from day one. Going round and round w/the installer. Not happy at this point, but fortunately we only have a few weeks of below 35 degree days where this is an issue. Any advice would be appreciated -- and I hope they get back to us if theirs ever gets resolved. Sure would like to know. Here's my problem detailed: http://ths.gardenweb.com/forums/load/hvac/msg0113541214362.html?5


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RE: heat pump blows cold air during defrost

same problem here...if you figered it out any updates would be appreciated. thanks


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RE: heat pump blows cold air during defrost

I too am having the same problem and very similar to Sparky. I too have a Goodman unit that was installed about 4 years ago and the outdoor unit replaced again after a year and it failed.

I too have just noticed cold air blowing out and apparently it is during the defrost cycle. I put a hout thermometer on it and it will normally run around 84 degrees at the register but at times will run about 68 degrees. The temp outside has benn mid 20s to mid 30s. The furnace guy came out and said the filter was plugged and had kicked out the heat strips. I questioned this, but figured he knew what he was doing. After he left if continued to happen and had him out again. He 'added' a board to turn the unit off during defrost. Doesnt sound like that can be done from what I read. In any case he left and the unit continues to do the same thing.

It sounds to me that the heat strip must not be coming on during defrost. What part that might be is probably the question.

Does anyone know if the heatstrips have an interanl 'breaker' or theraml cuttoff. I know I checked the breakers back at the panel and the breakers on the indoor unit and they were normal before the heater guy showed up and told me he had to reset these.

Any thoughts or possible solutions from the others that are experiencing the problems please let me know.


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RE: heat pump blows cold air during defrost

I have had the same problem with my Carrier HP (38QRR and FV4BN air handler) since it was installed 22 months ago. When in Defrost Mode, air temp exiting registers gets down to low 60s/high 50s (outside air temps 32 to 35 degrees). Strips operate in heat mode. Techs have swapped T-stats and changed from 10kw to 15kw strips with no affect.

I live in SOCAL, so problem occurs infrequently and season for trouble shooting is short; but on those occasions when system goes into defrost, the COLD blowing air is extremely uncomfortable. I would sure like to get problem corrected.


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RE: heat pump blows cold air during defrost

If the system was working corerctly and nothing else has changed, check the heater strips.

They can fail (either open or partly open).

I would disconnect each strip and see if the resistance is low (good) or high (open).

A 5,000 W, 240 V element should be around 20 ohms.


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RE: heat pump blows cold air during defrost

HP System has never worked correctly - has blown cold air during defrost since installed. Although the heat strips have always worked well in Heat Mode, they do not seem to come on in Defrost. Is it possible to check the operation of the heat strips in the Defrost Mode when the outside air temperatures are not low enough to cause the HP to go into the Defrost Mode?


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