heat pump problem

[Ralph Mowery]

I have a Trane heatpump that is about 12 years old. In the summer it cools fine. Last winter the house was about 2 deg cooler than the thermostat was set for. Noticed the inside air handler was running,but the outside unit was not.

Checked and had power. The relay that puts power to the compressor and fan was not pulled in. The coil did not have any voltage on it. The circuit board has a led that blinks once per second like the paper in the pump says it should if everything is ok.

I cut it off by the thermostat and then 5 minuits later turned it on. Everything is working fine now. The heatpump did that to be about 3 or

4 times last year. I don't recall the temperature then,but today it was about 40 deg F outside. It was 66 inside instead of 68 like it was set for.

I don't mind calling a man for service, but there would not be anything I know of for him to find. Any ideas on why the outside unit will not cycle off and on like it should ? Maybe it goes into the defrost mode and gets hung up ?

[trader_4]

IDK how heat pump systems call for heat. Is there one wire that says make heat, another one that turns the blower on? Or does one wire say make heat and the system turns the blower on? If it's the latter, then since the blower is running you can rule out the thermostat. If it's two wires, then it's possible it's a thermostat problem.

I agree that calling for service on something like this is really bad. They won't see it happening and even if they do, probably won't have any more idea what to do that you do.

[trader_4]

Another question, what does it do when it's 66/68 and you just leave it? Does it eventually come on? Does it go back on when it drops to 65?, etc. Or does the compressor just stay off indefinitely? What was it doing just before, was it maintaining 68? If so, then you'd think it must stay off a long time when it's 40 outside for inside to drop two degrees.

[gfretwell]

in the thermostat cable The white wire calls for heat (W2 calls the toaster wire) The green wire turns on the fan. Yellow is AC Going out to the condenser it is either an orange or blue wire that turns on the reversing valve (manufacturer dependent)

[Ralph Mowery]

I don't know how long it was off as it was 4 deg low when I got up this morning.

If I leave the unit along, the air handler keeps blowing and the outside unit never comes on. Last night the thermostat was set to 68 and the inside air was 64.

To start with I went out side and checked the relay that turns on the compresor and fan that blows on the outside coils. There was no power on the coil. Pushing it in manually and the units motors ran while manuallyh pushed in.

I cut off the power to the unit and 5 minuets later the power came back on (load control from the power compay has that built in delay external to the unit). Nothing any different.

Then went to the thermostat and set it to off. Waited about 2 minutes and turned it back on. The unit started up and has been working fine all day and to ten at night (which it is now).

[trader_4]

But when it calls for heat does the thermostat activate the W wire and the G fan wire? Or just the W wire? With furnaces, it only activates the W wire, the furnace then turns on the blower. The G wire in the furnace application is if you want to manually put the blower on, without heat. That matters with Ralph's problem. If it takes two wires to work it, then it's possibly a thermostat problem or issue with the W wire. If it just takes activating the W wire, then the thermostat and wiring aren't the problem, because his blower is running. I guess regardless I would get it set up so that I could measure the voltage at the W and G terminals at the air handler control board when it's having the problem. That might require taping over a cut off switch on a panel.

I'd also inspect the relay on the control board that drives the compressor unit, if possible. Maybe the relay is sticking/failing and sometimes it will not close to activate. He should also measure the voltage at the control board that goes to the compressor when it's having the problem, see if it has voltage or not. That would help determine if it's before that point or an intermittent wiring problem going to the compressor unit. But it doesn't seem like a wiring thing, since recycling the power restores normal operation. So far, it sounds most likely a control board problem.

If it looks like that's it, he could buy a new one. If it turns out that it's not that, very good chance he can sell it on Ebay and get most of his money back. Very cheap compared to what it would cost to call out an HVAC guy. the compressor.

[Ralph Mowery]

I worked for years as an electrician and instrument person at a large plant, so doing the actual work and measurment ( I have all kinds of test instruments at home) is no problem. I dealt with computer controled equipment and some 480 volt 3 phase heaters that pulled about 300 amps. Just knowing what to look for on this simple controller is my problem.

That thing just will not stay screwed up long enough to find the problem. It only does it a few times in the winter. Just started a year or two ago.

I did check the relay that powers the compressor and fan. It did not have any power going to them. Pushing it in by hand (screwdriver) starts them.

I may buy a control board off ebay. Seems that I looked into it last year but did not follow up when I bought a spare capacitor and relay just so I would have them at hand.

The board would be cheap compaired to calling the man. I learned my lesson on that a few years back when I was charged about $ 350 just to have the capacitor replaced.

[trader_4]

Don't you mean that it doesn't happen often enough? I thought you said that once it gets into it's off mode, it just stays there until you cycle power? At the very least, it must be staying like that for hours, if not indefinitely.

Exactly. And if you don't need it, you can resell it on Ebay and likely get most of your money back. That's how I look at many parts purchases today, when I'm not 100% that it's that part. It's one of the wonders of the internet age. Twenty five years ago, if you bought a part like that and you didn't need it, there was no way to sell it.

[gfretwell]

The heat will not run unless the fan is on and depending on the thermostat base, you might have to turn the fan switch on to get heat. I am not sure about furnaces, I haven't seen one in 35 years but that is how air handlers work. I do know you can run most heat only furnaces on a 2 wire thermostat (just reading the instructions for thermostats). He is definitely in the situation where poking around with a meter (even a 24v test light) and looking at the wiring diagram is in order. Just throwing parts at it and trying to get lucky is silly.

[gfretwell]

Since you do seem to have skills, it might be worth making up a test light with an LED and a 2k or so resistor and hanging it on the white wire and maybe another one on the green.. Then if that is OK start moving it closer to the relay that is not getting the pick shot. You can leave it connected and look at it when it is working, again when it is failing. In a few failures, you should be able to find the bad part.

[Ralph Mowery]

This is not a furnace, but a heat pump.

The fan on the air handler runs when it is calling for heat. It is the out side unit that is not running. The relay for it has no voltage going to the coil that tells it to pull in and run the compressor and the fan for the outside coils.

The thing acts up so infrequent it is difficult for me to do much but just want to get it started. I hate cold weather and seems like my brain freezes up when cold. I call anyting below about 50 cold being in the middle of NC.

[trader_4]

Furnace is as I described. The thermostat just calls for heat on the W wire (or wires if it's two stage), the furnace does the rest, ie turns the blower on after the furnace has fired for a minute or so. Old furnaces used to use a temp switch in the plenum to activate the blower. New ones just use a time delay on the controller board.

An interesting side note with two stage furnaces. They can generally be set up two ways. One is really the right and best way, which is to use two heat call wires, one for each stage. The other way is to just use one wire and set it up so the control board makes the call based on how long the furnace runs. So, it starts at low stage, then if it's still running after ~ 8 mins or so, it goes to high. Obviously that's far from ideal. If you need a bigger increase in temp, you have to wait 8 mins for it to kick up. And it also might kick up and then shut off in a just another short period, if the temp was almost where it needed to be.

The thermostat knows what the req increase is and can invoke high stage at the beginning. But it takes an extra wire, that many installs probably don't have. It also takes a two stage thermostat. I'd also bet that a lot of furnaces are installed using the inferior method anyway, because the installers are half-assed, don't want to change to a two stage thermostat, etc.

I do know you can run most heat only

Bingo.

He is definitely in the situation where poking around

I agree, I'd do more investigating, starting with what the voltages are at the inputs to the unit and at the activation terminal going to the heat pump.

[mkolber1]

heat pumps have a lot of crazy modes for defrost etc.

does yours also have resistance coils heating?

maybe it was in another mode?

m

[gfretwell]

The LED indicator will still be a way for a quick peek without having to get your meter out. I would start with it on the white wire from the thermostat inside the air handler and get that out of the picture. The first rule of trouble shooting is "can you draw a circle around the problem"? You want to get as much as you can outside that circle. You already seemed to have eliminated the condenser since you don't have the pick shot to the relay. If you eliminate the thermostat and wiring into the air handler you are getting pretty close to that control board. Do a visual inspection of all connections before you buy anything.

[Ralph Mowery]

One of my metrs is a Fluke T5-1000. Very handy as for checking voltages it goes from low voltage to high voltages and auto from AC to DC. Just slap the leads across a circuit and if any voltage from a volt or so up to maybe 1000 they will show up. It also does ohms and is very well protected. While at work using them, we would go across fuses on a 240 volt circuit and if the fuse was open, the meter took it just fine. It will also do AC amps like the clamp on type. All this about the size of a bannana.

My favorite for simple trouble shooting is a Fluke T2. Same size,but has about 8 leds on it that light up on voltages of 6 volts to 600 volts AC or DC. It will show continuenty of a circuit that has a very low ohms in it. Just 2 wires like the led thing you are talking about, but does much more.

I did take time today to pull the wiring diagram. If it stops on me again, I will try to follow the 24 volt control circuit to see where it stops. It must be in that as the relay did not have any voltage across it that starts the compressor and outside fan. They both run if I push the relay in with a screwdriver.

The control board is just a block with not much information on it. It does have a trouble shooting LED, but it blinks once per second like the paper says it should if nothing is wrong.

[gfretwell]

There must be a processor on that card. If the thermostat wires go right to the card and the connections are good you really only have the output to the relay. Maybe the driver transistor/Triac is bad. It might also look at the card to see if there is a flaky land pattern or a cold solder joint. Is this AC to the relay or DC? Typically HVAC is AC but I wouldn't be surprised that these CPU controlled ones use DC. If it is AC, you also have the connection from the AC supply into the card. The LED is really just the "heartbeat" indicating the processor is running.

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[Clare Snyder]

Personally "I" would start by checking ALL connections in the low voltage control circuit. clean all contacts to "bright" and reinstall with de-oxit or similar connection "dope". Any place with push or slide connections, buff the contacts with a hard pink eraser. Also trty wiggling any solid core wires to check for cracks, and check for ANY evidence of moisture, corrosion, or buf nests.

[Clare Snyder]

next time it doesn't run check for voltage out at the controller instead of voltage in at the contactor

[Clare Snyder]

+1

[trader_4]

Shouldn't even need a circuit diagram to trace the wiring. Look for the color of wires that drive the contactor outside and look for them in the cable coming from it to the air handler control board. Also the terminals should be marked with something that you can decipher by looking at it. If there is 24v there when it won't run, then wiring is the problem, otherwise look at what's at the W terminal from the thermostat.

It must be in that as the relay did not have any voltage across