AquaComfort Heat Pump Mystery - 24 Volt Breaker Tripping

[Chuck_Davis]

I have a 10 year old AquaComfort AC1250 heat pump. I just went through the repair/replace decision, and for now I'm still trying to repair. So far the heat pump is winning.

The 24-volt transformer, which powers the control board and, through the control board, all relays and sensors has a built-in breaker that trips as soon as I power up. I have replaced the transformer and the control board. One at a time I have disconnected all relays and sensors from the control board (both wires, in case something is shorting to ground), but the breaker still trips.

I'm getting 242-244 volts from the power company, but that is within spec for them.

Does anybody have any experience with this kind of problem, probably in your "Dang, That's Weird" file?

Thanks.

 

[ajw22]

You examine the control board for burn marks or burnt components?

What amp is the breaker? Have you considered replacing the breaker?

Put an ammeter in line with the breaker and see what amps are being pulled when it trips.

 

[Chuck_Davis]

You examine the control board for burn marks or burnt components?

What amp is the breaker? Have you considered replacing the breaker?

Put an ammeter in line with the breaker and see what amps are being pulled when it trips.

Control board looks good. It's not the breaker at the panel that is tripping. It's a 240/24 volt transformer, and the breaker is on the 24-volt side (literally) of the transformer. Breaker on both old and new transformers is tripping. I'll try the ammeter next time I go in. Thanks.

 

[ajw22]

I would look very carefully at the wiring harness. You may have had a critter chew on the wiring.

It helps to know what that 24V breaker trip rating is. No markings on it?

Post a pic of it and the transformer.

 

[Chuck_Davis]

The 24-volt breaker is a rocker in the black square to the right. On the old (but probably still good) transformer the breaker is labeled as 4 amps. Most of the wiring is inside a critter-proof metal box, and I haven't seen any evidence of munchies. If one of the sensor runs outside the box had been compromised, it should have been isolated when I disconnected (both wires of) each run in turn.

Wiring diagram is on Page 6 of: https://www.google.com/url?sa=t&rct...s-Manual.pdf&usg=AOvVaw26xjE5wm2FcPYJMi-Ycc9w

I assume the breaker is inline on the yellow wire.

 

[ajw22]

Find the FAN1 relay coil and the COMPRESSOR CONT ACTOR (CC) relay coil and test with a multimeter if they are shorted.

Looking at the wiring diagram on page 6 it looks like those two relay coils or the Microprocessor Control board are the things that could short out the 24V.

 

[Chuck_Davis]

Find the FAN1 relay coil and the COMPRESSOR CONT ACTOR (CC) relay coil and test with a multimeter if they are shorted.

Looking at the wiring diagram on page 6 it looks like those two relay coils or the Microprocessor Control board are the things that could short out the 24V.

I know, but..................

Control board was replaced with a new board, but the breaker on the transformer continued to trip. (I reinstalled the old control board. I hope I can get an RMA for the $500 control board.)

If I disconnect both wires from the control board to the contactor (CC, Black/White & Violet), the breaker still trips.

If I disconnect both wires from the control board to the blower relay (Fan 1/RB, Blue & Orange), the breaker still trips.

If I disconnect both wires from the control board to every other switch or sensor (one pair at a time), the breaker still trips.

I'll throw the ammeter on the coils tomorrow, but I would think that disconnecting the coils from the control board should eliminate them as suspects,

This is why I suggested looking in the "Dang, that's weird" folder. I'm totally stumped. (Or missing something totally stupid.)

 

[ajw22]

That all points to a chafing of the wiring somewhere that shorted it. It is probably in a hidden place that is hard to see where the wiring makes a turn. I have dealt with hidden chafed wires in aircraft systems.

You have to use the multimeter continuity tester to find continuity between wires where it should not be there. You have to disconnect both ends of the wires for testing. It can be tedious work.

 

[Chuck_Davis]

That all points to a chafing of the wiring somewhere that shorted it. It is probably in a hidden place that is hard to see where the wiring makes a turn. I have dealt with hidden chafed wires in aircraft systems.

You have to use the multimeter continuity tester to find continuity between wires where it should not be there. You have to disconnect both ends of the wires for testing. It can be tedious work.

I'll take another run at it tomorrow. Except for the contactor and blower relay, the short would have to be in the harness between the control board and terminal strips (which is where I lifted the wire pairs). I did lift the wire pairs at the contactor and blower relay, so a short could be between them and the control board.

Staring at the control board, I just realized that there is one other wire run I haven't checked. The 4-wire harness from the control board to the touch pad (interface panel). It could also be the touchpad itself.

Thanks for the suggestions and taking the time to cogitate with me.

 

[Chuck_Davis]

I'll take another run at it tomorrow. Except for the contactor and blower relay, the short would have to be in the harness between the control board and terminal strips (which is where I lifted the wire pairs). I did lift the wire pairs at the contactor and blower relay, so a short could be between them and the control board.

Staring at the control board, I just realized that there is one other wire run I haven't checked. The 4-wire harness from the control board to the touch pad (interface panel). It could also be the touchpad itself.

Thanks for the suggestions and taking the time to cogitate with me.

The good news is that with ajw22's coaching I discovered a thin wire running to the frost sensor that had chafed against a piece of tubing and was shorting to ground.

The bad news is that the shorted wire had fried my original control board. This in turn caused the breaker on the 24-volt transformer to continue tripping. I.e. it was the control board tripping the breaker, not the original short.

The really bad news is that the shorted wire had fried the $500 replacement control board.

An important lesson is that if the breaker on the 24-volt transformer is tripping, it would be wise to isolate each wire from the control board (at the terminal strip) and test for a short from the terminal strip to ground as a first troubleshooting step. Your control board may already be fried, but you can potentially identify the root cause of the problem and avoid frying another control board. This is my scar tissue talking.

Another important lesson for anybody else troubleshooting an AquaComfort system is that if you want to disconnect a switch or sensor from the control board, don't just disconnect the wires to the switch or sensor. You have to short the pair of wires coming from the control board. (I learned this yesterday from the local pool store heat pump technician.) My belief that disconnecting the wires isolated each sensor for troubleshooting misled me.

An important lesson for probably all owners of heat pumps is to periodically inspect your unit for potential chafe points and tape up the wires at those points. This is more of my scar tissue talking.

 

[ajw22]

Those are all good tips for troubleshooting lots of complex equipment.

Glad you found the short.