Goodman Heat pump not running. Very detailed.


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Old 10-03-15, 02:08 PM
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Goodman Heat pump not running. Very detailed.

Hello all,
New member here looking to get some input on an home AC issue. Just a quick bit on me. I work on medical imaging equipment, ie, generators, small refridgeration systems, low voltage, and misc stuff like that, so I'm a complete newb.

Now here's the issue. I came home a couple days ago and found the outdoor unit was not running. It's a 3yr old (was at home when we bought it) goodman GSZ130301 heat pump (heat and cooling), and a goodman indoor air handler.

The thermostat was on and showing cooling, and the air handler was pushing air. I had a similar issue at the beginning of the summer with my downstair unit. So, I check breakers and obvious stuff like thermostat off/on. I pulled the panel off the outside unit and tapped the contactor and it started running. Thinking this was the issue I went back inside to adjust the thermostat because it was hot in the house and the thermstat went crazy. It was a honeywell touchscreen, and all the segments on the display would light up, then dim continuously. At that point I thought it was the thermostat so I bought another.

I wired in the new thermstat and same as before, no outside unit. Here's where I start getting stumped.
At this point I assumed my 24v transformer or contactor. So I went outside and measured pole to pole on the low voltage side of my contactor, no volts present with a call for cooling. I go inside and measure the output of the 24v contactor and have 27v solid. I happened to have extra parts from my last AC adventure, so I swapped the contactor and 24v transformer. No change.

I should mention that I can push the plunger on the contactor and the compressor and fan will run, as long as I'm pressing it.

I then start troubleshooting the circuit board and attached parts in the outdoor unit. Both the low and high pressure switches are OK. After more troubleshooting I thought it could be the board. I order another, put it in and same results. There's numerous measurements and troubleshooting involved in the above, but I'll give the jist of it below.

I started trying to figure out where my call for cooling or heat signal was dropping off, and found this strange. Heres how the board is wired

R - R from thermo
Y - Y from thermo through high pressure switch
C - from C at therm goes direct to contactor and splits to board.
CNT - from board to other pole of contactor. CNT and C are supposed to pull the plunger in

If I put my meter on both contactor poles, I get no voltage (0.3 or so). Now if I disconnect the Y from the board and measure the cable direct, I get my 27v, so I know I have a call for cooling. If I take the Y cable and plug it directly into the contactor in place of CNT, I still get no pull on the plunger.

If I disconnect CNT from the contactor and measure it to C, I show about 9v. This makes me think it was a board/switch. But why would the contactor not pull when I directly apply 24v to it? Y - C I've tried 3 contactors, and swapped 2 into my other unit and they work fine. I've tried 2 transformers and 2 circuit boards. I have jumpered the high and low pressure switch (just as a test). Also borrowed the thermostat from other unit, no luck.

I tried to ohm out my 24v wiring thinking i may have a short, but from what I can tell everything is good.

I tried taking the incoming Y and C signal direct from thermostat and connecting to both poles on the contactor (bypassing the board altogether) and still get nothing. The contactor make 0 attempt to pull in. I am very stumped at this point.

I have verified that the contactor, transformer, and thermostat all work on my other AC unit (rheem).

I also troubleshot inside at the air handler, making sure one of my condensate switches wasn't causing issues, completely removing them.

I removed the thermostat and physcially jumped R-Y-G, air handler comes on as expected, still no outside unit.

I have all but given up at this point, but since it's Saturday I have to wait until monday to anyone. I figured I would post my tale of woe here and see if anyone has any new ideas. Sorry this was so long winded.
 
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Old 10-03-15, 04:56 PM
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You need to determine whether the problem is with the outside unit or inside the house. Here's what I would suggest you try. With the thermostat calling for cooling, check where the low voltage (24VAC) control wire comes into the outside unit. There should be wire nuts connecting the wires coming from the house to the internal wiring. Measure the voltage across the wire nuts. Ideally, you should measure ~24VAC. If you do measure 24VAC at the wire nuts but no voltage at the control terminals on the contactor, you have a problem in the outside unit. If 24VAC is not present at the wire nuts, then the problem is either inside the house or the wire from the house to the outside unit is bad.
 
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Old 10-03-15, 05:00 PM
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Thank you for the advice. I just took a spare contactor and created 2 small leads off of each pole. I then went up to the Air handler and tapped into the Y and C coming out of the air handler going to the outdoor unit. The contactor pulled closed immediately. Doing the same outside nothing happens. Looks like I am tracking down a short in the wiring between AH and Heat pump.

Thanks,
 
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Old 10-03-15, 05:09 PM
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Not a short..... an open or broken cable.


In the future....
Check for 24vac at the air handler (Y to C).
Check for 24vac at the contactor.
Check for 24vac right where it enters the condensor.

This way you know right where the problem is. Divide and conquer method.
 
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Old 10-03-15, 05:46 PM
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As Pete mentioned, you should check to see if you have 24VAC where the voltage comes into the outside unit. That's what I was trying to tell you to do by measuring the voltage at the wire nuts. If you don't have voltage where the control voltage comes into the outside unit, in addition to a possible open wire from the house, it's also possible that you may have a problem with the air handler control board if the signal passes through it.
 
 

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