3 AMP fuse bowing on Goodman heat pump

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Old 11-11-18, 05:21 PM
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3 AMP fuse bowing on Goodman heat pump

I have a goodman heat pump. Weather just got cold and heat is now on. The issue is that the 3 AMP fuse started blowing a few days after we turned the heat on.

I have isolated the outside unit (breaker off and disconnected the control wires) and no issues.

I connect the Common and 24 volt power wire to the exterior unit (breaker still off) and the 3 amp fuse blows.

Given that it ONLY the common and power wire (C and R wires) I am thinking it is the control board in the exterior unit.

Should I check anything else before I order a board.?

Thank you
 
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Old 11-11-18, 07:08 PM
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You’ll have to trace wiring. Control voltage runs all through the outdoor unit, including any pressure safely controls the unit may have.
Don’t assume anything before diagnosing.
 
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Old 11-11-18, 07:34 PM
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Welcome to the forums.

You need to keep in mind that the C wire is basically ground so any short in the thermostat or control wiring to ground is a system short. Apparently you've confirmed the problem is in the condenser. Now you need an ohmmeter to trace the (R) red wire.
 
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Old 11-12-18, 03:56 AM
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Thank you Roughneck and PJmax.

I am waiting for the sun to come up and then will head back to the outdoor unit. I hope to get some of the trace done before it starts raining...

I was chatting with another friend and they recommended looking at the contractor and then looking for a worn wire. Since the system has worked without issue for the year, they were saying it was likely something mechanical going on (vs the control board having an issue).

PJmax: As for the common being ground, yes... Given that the Air Handler operates without an issue if the control wires are disconnected that the exterior unit am I same to conclude that the issue is in the exterior unit or should I also do a conductivity check on the Hot and Common (those were the only two wires connected the last time I blew the fuse)

Oh, and I did test and confirmed that I was getting 27 volts across the Hot and Common.

Thank you for your help.

Greg
 
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Old 11-12-18, 05:39 AM
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Continuing information on the low voltage electrical issues.

I have traced the control wires from the inside to the outside and found no breaks or damage .

I did an ohm check across the coil in the contactor and found 13 ohm. I think it is suppose to be around 20. Is 13 in the ballpark?

Each side of the coil to the metal of the case shows more than 300 so that appears to be ok.

Thanks

Greg
 
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Old 11-12-18, 10:30 AM
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Each side of the coil to the metal of the case shows more than 300 so that appears to be ok.
If that was the contactor coil you were checking..... you need to check it with no wiring on it when checking to ground. 13 ohms on the coil is fine. There should be no continuity measured from either terminal to ground.

The R/red wire and the C wire carry 24v power to the condenser at all times. The Y/yellow wire only gets power from the stat to operate the contactor on a call for the compressor to run.
 
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Old 11-12-18, 11:48 AM
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Good afternoon PJmax

Thank you for your reply. Here is what I have found thus far.

1) Across the coil with no wires is 12 AMP. On an identical unit that we have at the house, the coil is 17 amp. Not sure that is an important difference. I also tested to the metal case and indicated more than 300 ohms between each post and the metal housing. No issues there.

2) I disconnected the control wire at both ends and tested with an OHM. No issues. Tested no shorts or faults.

3) Disconnected one wire to the coil, connected the Common and HOT (24 volt) on the outside unit, and tried it. No fault.
Then connected the coil wire and tested. No Fault.
Then connected all of the individual control wires one at a time and tested each. No Fault found.

The system is running again, without any diagnosis of the issue.

I am going to order a new contractor (and some more 3 amp fuses!! HAHA). Given what we have found thus far, I am thinking that the contactor is slowly failing.

The saga shall continue... at some point... I am sure... but just dont know when.

Feel free to send additional comments.

Thanks

Greg
 
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Old 11-12-18, 12:37 PM
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1) Across the coil with no wires is 12 AMP. On an identical unit that we have at the house, the coil is 17 amp. Not sure that is an important difference. I also tested to the metal case and indicated more than 300 ohms between each post and the metal housing. No issues there.
Ok..... that is 12 ohms you measured. Another measured 17 ohms. The 12 ohms could be slightly low and could cause the fuse to blow when combined with the other electronics connected to that 3A fuse.

A little confusion here. The wires on the side of the contactor are for the coil. If you have removed those wires from the coil and you can measure anything from those terminals to ground.... or the metal frame.... that contactor is bad. There should be no resistance measured from those coil terminals to ground. Any resistance measured means the coil has shorted.
 
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Old 11-12-18, 12:41 PM
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PJmax
Thanks. I will go back down and confirm with both coil wires removed that the reading to metal case is OL. It was between 300 and 400 ohm, and I thought that was enough to be ok.

However, I concur with your line of thinking that the contractor is going bad or is bad. The unit is running so I am working on ordering a replacement contractor from Amazon along with some more 3 amp fuses (the local auto supply store is of of stock after this exercise. HAHA.

Thank you for your help.

Greg
 
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Old 11-12-18, 12:43 PM
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The coil on a contactor is completely insulated from ground.
If it shows resistance to ground.... the coil has burned.
 
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Old 11-25-18, 08:07 AM
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Good morning.
Guess what has failed, again. Yes the goodman is off line, with the same exact symptoms: the 3 amp fuse on the interior air handler blows when 24 volt power is applied to the exterior unit.

Today I have done the following:
1) Ohm tested the control wire, no issues identified.
2) Replaced the contactor (it was testing low on the coil and had one, so might as well).

This has not corrected the issue.

I have removed the power to the coil on the contractor, to completely isolate that, and the 3 amp fuse still fails.

Therefore, I can only see the coil on the reversing valve or the control board being a point of failure now.

My plan is to remove the wire going to the solenoid and then testing the unit again. If the fuse holds, it is the solenoid. If the fuse blows, it is the control board.

1) How does that sound for a plan?
2) I am trying to research the nomenclature on the control board (Model pcbdm133 for a goodman) to determine which is the solenoid. Any ideas on which it is or where to look?

The internet says to look for the RVC (Reversing Valve Coil), I find a C-rv post. Is that Coil - Reversing Valve?

thank you for your help

Greg
 
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Old 11-26-18, 03:29 AM
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Good morning
Just wanted to post an update. I went through the diagnosis, finally narrowed it down to the pressure sensor.

Opened up the unit and found where the wire had rubbed to bare metal and caused a short to ground.

Electrical tape, followed by a couple layers of duct tape, and the issue is solved. (or at least the unit is working again).

All the best

Greg
 
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Old 11-26-18, 09:54 AM
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Good job. That does happen sometimes from the compressor vibration.
 
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