Basement A/C Control Board Fix

[NR4A]

After our Basement a/c died on us a few days after delivery, it was diagnosed with a control board dysfunction. Our dealer was nice enough to mail us a new control board, which brought us back to life after I installed it.

Being an electronics geek, I tried some reverse engineering on the controller they're using on this unit. With an ohmeter I did some static checks of the components and alas, found the culprit.

There are 2 resistors in parallel at 27K ohms 2 watts on the bottom of the board marked R48 and R16 that were found to be open.


There is also another pair, also 27K ohms, marked R82 and R17 also in parallel. Total measured in-circuit resistance is about 12.5K ohms.

Replacement of the open pair breathed life back into my (now spare) control board. I only had some 3 watt resistors in my junk box (yes, 3 watt) and got them soldered in nicely. My spare works like new, maybe better than new(?)

If you ever have your board out - you will see some heat discoloration on the board and on the connecting traces. This is from the resitors heating up over the years.

DO NOT EVER CHECK THESE WITH POWER APPLIED !!



There is approximately 150 VDC on the input of these resistors, and 1.2 VDC on the output side feeding an opto-isolator. The original resistors are carbon film, my replacements were carbon filled.

Hope this tidbit might help someone out in the future. The new boards are $250.00 if you ever need to replace yours.

Motor Safe !

[NR4A]

After our Basement a/c died on us a few days after delivery, it was diagnosed with a control board dysfunction. Our dealer was nice enough to mail us a new control board, which brought us back to life after I installed it.

Being an electronics geek, I tried some reverse engineering on the controller they're using on this unit. With an ohmeter I did some static checks of the components and alas, found the culprit.

There are 2 resistors in parallel at 27K ohms 2 watts on the bottom of the board marked R48 and R16 that were found to be open.


There is also another pair, also 27K ohms, marked R82 and R17 also in parallel. Total measured in-circuit resistance is about 12.5K ohms.

Replacement of the open pair breathed life back into my (now spare) control board. I only had some 3 watt resistors in my junk box (yes, 3 watt) and got them soldered in nicely. My spare works like new, maybe better than new(?)

If you ever have your board out - you will see some heat discoloration on the board and on the connecting traces. This is from the resitors heating up over the years.

DO NOT EVER CHECK THESE WITH POWER APPLIED !!



There is approximately 150 VDC on the input of these resistors, and 1.2 VDC on the output side feeding an opto-isolator. The original resistors are carbon film, my replacements were carbon filled.

Hope this tidbit might help someone out in the future. The new boards are $250.00 if you ever need to replace yours.

Motor Safe !

[dstinch]

well i just learned something! thank you Don

[NR4A]

You are very welcome, Don.

Hope this helps someone someday!!