[bikestuff]

Gurus,

I think I am the first to have an basement AC SCS control board burn up with the external relay fix already implemented.

Right now, I am in the early stages of investigation but here are the highlights so far.

I have been away from the coach for a couple of weeks.   I found that the front AC was not running.   Checking the breaker showed that the #1 circuit of the front AC was tripped.   I foolishly simply tried to reset the breaker and it acted weirdly.  After a couple of tries it reset and stayed that way.  (I will talk about this more down below).

I went to the AC unit and pulled off the metal cover where the control board is.

Here is what I found:
   

Note the burned spot in the upper left corner where the AC for the #1 circuit enters the board.

I turned off both breakers to the front AC unit and removed the board:
           

It’s clear that there was a melt down on the AC connector.  Also, the board seems to have already been repaired since one of the traces has been beefed up.

Here is where it gets weird….

The bottom white connector where the #2 circuit enters the board was also loose!!!!  (Like barely hanging on) but there was no visible scoring from arcing. 

Newell has a company that is manufacturing replacement boards for the old SCS AC units.   They are pretty pricy at around $700…. But they are much more robust than the original SCS boards.

   

So…what caused the board to melt?  In my mind there are two possible scenarios.
1) The white connectors had bad solder joints and just gave up.  This caused heat to build up and eventually catch fire.   
2) Either of the fan motors are pulling more amps than they should and the excess current burned the board.

Remember that I already have the external relays so any excess draw from the compressors will be protected by the breaker in the breaker panel.

Since the current for the fan motors still goes through the board, I attempted to troubleshoot them.  I measured the resistance of the wires that go to the evaporator blower (inside) and condenser fan (outside).   Here are the results:

EVAP
C - L (red to white) 6.0 Ohms
H - L (Red to black) 2.6 Ohms
H - C (Black to white) 3.4 Ohms

Condenser
C - L (red to white) 8.0 Ohms
H - L (Red to black) 4.1 Ohms
H - C (Black to white) 4.1 Ohms

All wires showed open between the wire and the chassis.  

My amateur view of these readings say that the motors look good.   No shorts, and no opens.  It looks to me that the SCS board just decided that life was too hard and self destructed.

My plan is to install the Newell version and then measure the current draw on the fans motors as well as the compressors.   I will keep ya’ll posted on the results.

Cheers,
Bill

Ps.  About the breaker.  I should not have tried to reset the breaker until I at least looked in the wiring box of the AC unit.  I know that breakers fail….but if I had it to do over, I would not have been so quick to reset.   It only took a couple of minutes to get into the wiring box and find the burned wire.