Hi there... This is my first question and I would appreciate your expert help:

The circuit breaker for my Trane central air unit tripped and upon further investigation, I found some sort of short circuit behind the Integrated Furnace control board CNT 2789. I saw a big spark behind the board when I tried to activate the fan and I need to know if I should replace the board or first check if the fan is actually working. Is it common for these boards to go out? I know I can replace the board but I need hints on what else to check first.

Is CNT 03797 the correct replacement for CNT 2789? It looks different!!

Thanks for your help.

Ruben

You better find out for sure what caused the board to go out because if you just replace it with out finding a problem it might also burn out.

This might be best left to a professional since if they burn the new board they have to replace it for free. Just a thought.

Remember your going to see the flash at the weakest point in the circuit. You can have a grounded motor or anything and get a flash at the control board. I agree with hvac1000 I would get it checked out before throwing good money at something that is not bad.

Than you for the good advice to both of you. I will get it checked out.
>> By the way, now my second unit just went out!! I don't know if it is the same issue or not but I will have to have someone check it out. Is it common for the control boards to go out? These Trane units are 10 years old and have been working great so far...

Thanks for your help.

Ruben

There appears to be next to zero surge suppression on these boards and their expensive. It might be wise to invest into a furnace surge suppressor especially if power in your area is unreliable. Every hit degrades something a little until finally it doesn't work any more.

Thanks for the information.

It is disturbing that both units went out within a few days. I wonder if we have been having power surges... Would the board go out or short-circuit as a result of the fan going out? I am OK if the board went out because it got old. Has anyone else found other reasons for the board to go out? Or is this more common than I thought...

Thanks

There are mechanical parts on the board, the relays. They do not have infinite life.

Purely electronic parts can last nearly forever, HOWEVER for that to happen some engineering has to take place to protect against such failures. The fuse is the simplest of protections.

Spikes, surges, brownouts take expensive components to protect against and when multiplied by the number of units, leaving them out makes profit go up.

I want to thank you all so much for your advice regarding the control boards in my AC units. I replaced both boards and they are working well.

Both boards shorted out in the same place. It appears that the leg of one of the relays has been arking against the metal support for a long time and it finally burned out. I could not see where it went so I had to by new boards. Howeve, I insulated the metal support with electrical tape to prevent any further arking and possibly extend the life of the new boards.

Thanks for all your help. :)

I think I have the same problem you had - I saw a black spot on the metal support (back plane) that is not too far away from the cnt 2789 board. Of course the cnt 2789 was fried and I do not have blower to force the air out of the furnace (hence heat up the house). Using electric tape is a great idea! They should have designed this thing so the metal surface is not as close to the back of the cnt 2789 - that should not make their profit go bad much. Well, I guess having people buy replacement board for the ones burnt out by bad design DOES contribute to their profit no?

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Originally Posted by Ruben V

I want to thank you all so much for your advice regarding the control boards in my AC units. I replaced both boards and they are working well.

Both boards shorted out in the exact same place. It appears that the leg of one of the relays has been arking against the metal support for a long time and it finally burned out. I could not see where it went so I had to by new boards. Howeve, I insulated the metal support with electrical tape to prevent any further arking and possibly extend the life of the new boards.

Thanks for all your help. :)

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The electrical tape works great! If your board is fried, it is very easy to replace. Make sure you mark all the wires to ensure they go to the correct places...

Good luck.

Ruben

Thanks! I was able to fix the board by resoldering the disconnected relay pin on the cnt 2789 IFC board, and it works OK now!

Quote:

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Originally Posted by Ruben V

The electrical tape works great! If your board is fried, it is very easy to replace. make sure you mark all the wires to ensure they go to the correct places...

Good luck.

Ruben

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