Add to you checklist - Printable Version

Add to you checklist - Printable Version

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+--- Thread: Add to you checklist (/showthread.php?tid=2466)

Add to you checklist - Richard - 08-12-2015

After reading Bill's post of the mini fire in his AC control panel, I thought to myself, that I should open both panels and snoop around. But, I didn't.

Last night the front AC wasn't blowing cold air. Today's investigation revealed an overheated and degraded splice in compressor number one wiring. It was a quick fix but it did bring up some things that I thought I would kindly mention.

I have had three similar occurences in my 9 year Newell ownership where an electrical connection degraded and melted. ALL were in the AC control boxes. There is a lot of current driving the compressors, and in my opinion the wiring on the boards and from the boards to the compressors in undersized. The bad connection at best creates heat and melts the wiring. At worst it just reduces voltage to the compressor and fries it instead. I could have easily had the same fire that Bill did.

The second location for electrical thermal issues is the 50 amp plug. The screws holding the wiring to the lugs loosen over time.

The point is to add these locations to things you check from time.

When we get home, I have a AC project that I will report on. With input from Russ I am going to add external high amperage contactors for the compressors similar to what you would find on a home unit. I also will replace in the splice in the system with soldered connections.

RE: Add to you checklist - bikestuff - 08-13-2015

Richard,

Thanks for the report. I am trying to decide what to do with my basement AC units. If there was an external contactor device that would handle the high current switching, I would feel much better about these units. I suspect a contactor box could be made pretty easily and would work in conjunction with the control boards.

For those following this thread and have basement airs...please note...

1. The "fault" did not appear to originate at the screw connectors. (I had assumed that was where the problem was and had been checking prior to the incident). Look for any degradation on your control boards.
2. Just because you have not had any AC issues, does not mean you don't have a problem. This incident happened on the rear unit. (The one that had never, ever given me any trouble).
3. Don't think that the breaker will save you. It did not ever trip in my case. The only thing that happened was that the fuse supplying the thermostats popped.

As my high school chemistry teacher (Mr. Harris) said...."A word to the wise is sufficient".

RE: Add to you checklist - Richard - 08-13-2015

Bill,

I am going to take the 120 VAc that would normally come from the board to the compressors, and trigger the contactors with that. It's a bit of extra, but simple wiring. So it will take the 15 amp compressor current completely off the board. In the past others have had either compressor relays or the compressor supply circuits fail on the boards. The fans don't draw much current so I won't fool with them.

One could pull the 12v signal on the board to trigger a contactor, but that seems like a lot of extra monkeying around.

I will put the contactors in an external electrical box just outside the SCS unit. It doesn't make sense to cram them into the space with the board.

RE: Add to you checklist - encantotom - 08-13-2015

sounds like an easy project. there is no room in there with the boards anyway

tom

RE: Add to you checklist - Chester Stone - 08-13-2015

Richard, when you get this designed some of us would like to copy your work. Perhaps it is something you can make up and sell to us.

RE: Add to you checklist - Richard - 08-13-2015

Or maybe a project for SCS equipped coaches at the next rally.............

RE: Add to you checklist - bikestuff - 08-14-2015

Richard,

Ok, so how does the board get its power to do its thing, or is it a simple relay and needs no power?

bill

RE: Add to you checklist - RussWhite - 08-14-2015

The board uses two, well three actually, sources of power. Two 115vac feeds, each with their own breaker, and the 12vdc power contained in the cable from the thermostat. There is at least one 115VAC relay on the board, but most have 12vdc coils.

I agree that additional heavy duty relays would be best located outside the existing enclosure.

If I were doing the job ( I'm not as I am reluctant to fix what I fixed before until it breaks again :-) ) I would simply replace the two compressor relays with external higher rated relays ensuring compressor current is no longer on the board, and call it done.