Hello,

Does anybody have any experience replacing the control board (CNT 03798) on a trane unit? I had an HVAC guy check out the unit, and he told me that was the part that needed replacing. I'd like to do it myself to save several $100.00 on the job, but I've never done it before.

It doesn't look too difficult as the board is easily accessible, I was just wondering if anybody has done it and has some advice, tips, tricks to getting it installed correctly.

My plan is to hold the new unit up to the old and one-by-one unplug all the wires going into the old unit into the same spot on the new unit. Sound like a good plan?

Thanks in advance,

Matt

Turn off all power to unit. Change wire for wire from old to new. Look at the board and make sure they did not change it. Look for the instructions in the box if there are any and read them first. Should be easy.

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Originally Posted by hvac1000

Turn off all power to unit. Change wire for wire from old to new. Look at the board and make sure they did not change it. Look for the instructions in the box if there are any and read them first. Should be easy.

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Hvac,

Thanks for the reply! I have a question, what do you mean by "Look at the board and make sure they did not change it?"

I checked the part number of the board that they claim needs replacing, it is listed as CNT 2789. CNT 03798 looks pretty much like it, but I'm finding CNT 03797 listed as the replacement for CNT 2789 on all the online sites I've searched, however, CNT 03797 doesn't look much like the 2789.

Is that confusing enough for you?

Thanks again,

Matt

I am talking about where the wires plug in and stuff like that. When you replace a board you want to make sure that A goes to A and not the location where A was on the old board but the A location might have changed on the new board.


In other words double check the wiring before and after the change to make sure of no mistakes. You will find there is no warranty on circuit boards/electrical parts purchased by a home owner. The reason for this is what I am telling you to look out for. When a board is sold to a professional there is a warranty because it is assumed that the pro knows what he is doing and would not short out the board by mis wiring it.

Quote:

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Originally Posted by hvac1000

I am talking about where the wires plug in and stuff like that. When you replace a board you want to make sure that A goes to A and not the location where A was on the old board but the A location might have changed on the new board.


In other words double check the wiring before and after the change to make sure of no mistakes. You will find there is no warrenty on circuit boards/electrical parts purchased by a home owner. The reason for this is what I am telling you to look out for. When a board is sold to a professional there is a warrenty because it is assumed that the pro knows what he is doing and would not short out the board by mis wiring it.

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I understand! Thanks again for the feedback.

I think that board is pretty much the same , like hvac said watch very close to what you are doing, each terminal on the board is labeled, one wire in the wrong spot may trash the whole board. Good luck and if you question any connection do not power up the system, get back on here and we'll be happy to help you through it.

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Originally Posted by hvacservicetech_07

I think that board is pretty much the same , like hvac said watch very close to what you are doing, each terminal on the board is labeled, one wire in the wrong spot may trash the whole board. Good luck and if you question any connection do not power up the system, get back on here and we'll be happy to help you through it.

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Thanks!

You have been very helpful! I got the replacement part yesterday, but we didn't get home until late, so I will try and install it tonight!

When the service guy came out, he bipassed the control board so that the fan would run and circulate air, so I have a few plugs unplugged that may make things take a little longer, but the blower door has the wiring diagram on it, and the WR instructions look pretty good.

Just from eye-balling it, it looks like the replacement board has all the same labels and connections in the same places as the original board, but I will tripple check it all before powering it up!

Again, thanks for all the help,

Matt

I'd say the fan relay went bad on the board, all he did was pulled a fan wire off and wired it direct, what color is the wire that he pulled off?

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Originally Posted by hvacservicetech_07

I'd say the fan relay went bad on the board, all he did was pulled a fan wire off and wired it direct, what color is the wire that he pulled off?

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Looks like he took the cool-H (I think) line out of the switch and ran the line that plugged into the c. board (another cool-something) directly into the fan switch. So he had the line coming from the fan plugged directly to the switch.

Btw, I got the control board installed. It seems to be working, I followed the instructions and put the therm. On heat about 5d hotter than room temp. It fired up just like the direction said it would.

The only thing I'm nervous about is that he also unplugged two red wires from the thermostat and I guess from somewhere else. They plugged into the YGRC, etc. screws on the bottom of the C. board. I re-wired them, one to Y and one to C. Am I okay here? Thermostat works for both hot and cold now w/ the new board in place.

Thanks again folks,

Matt

Matt,

I see to have the same problem - the cnt 2789 board has a few burning marks on the back. I need to replace it.

What board did you use eventually? CNT03797 I guess?

Thank!

Quote:

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Originally Posted by MattTVI

Looks like he took the cool-H (i think) line out of the switch and ran the line that plugged into the c. board (another cool-something) directly into the fan switch. So he had the line coming from the fan plugged directly to the switch.

Btw, I got the control board installed. It seems to be working, I followed the instructions and put the therm. on heat about 5d hotter than room temp. It fired up just like the direction said it would.

The only thing I'm nervous about is that he also unplugged two red wires from the thermostat and I guess from somewhere else. They plugged into the YGRC, etc. screws on the bottom of the C. board. I re-wired them, one to Y and one to C. Am I okay here? Thermostat works for both hot and cold now w/ the new board in place.

thanks again folks,

Matt

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Matt,

I seem to have the same problem - the cnt 2789 board has a few burning marks on the back. I need to replace it.

What board did you use eventually? CNT03797 I guess?

Thank!

Quote:

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Originally Posted by MattTVI

Looks like he took the cool-H (i think) line out of the switch and ran the line that plugged into the c. board (another cool-something) directly into the fan switch. So he had the line coming from the fan plugged directly to the switch.

Btw, I got the control board installed. It seems to be working, I followed the instructions and put the therm. on heat about 5d hotter than room temp. It fired up just like the direction said it would.

The only thing I'm nervous about is that he also unplugged two red wires from the thermostat and I guess from somewhere else. They plugged into the YGRC, etc. screws on the bottom of the C. board. I re-wired them, one to Y and one to C. Am I okay here? Thermostat works for both hot and cold now w/ the new board in place.

thanks again folks,

Matt

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I doubt you will get a response from the OP as his issue was resolved nearly 2 years ago.

Yep . LOL

Yeah I figured it would be a long shot.

Anyway my friend who used to work in a QC dept of an EE company told me to just solder the relay pin and the circuit board and that should be good enough. Is that a safe solution? He worked as a QC guys and he fixed many many "dead" electronic devices that way in the good old days when things were actually fixable...

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Originally Posted by hvac1000

Yep . LOL

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It's probably not a question of safety, but rather reliability. If the board is already toasty you have nothing to lose. It may get you through a pinch, but I wouldn't rely on it as a long-term solution.

Yeah I think so too. As long as it is safe, I will do that and get the heat going... it's cold in New Jersey now and HomeDepot does not carry the part :-)

Thank you all!

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Originally Posted by KC13

It's probably not a question of safety, but rather reliability. If the board is already toasty you have nothing to lose. It may get you through a pinch, but I wouldn't rely on it as a long-term solution.

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Matt,

I just burned out my circuit board for my compressor fan motor on a Trane XE 900. I'd alos like to replace it. Where did you find the replacement board?

Thanks,
Vic

Go to furnaceparts.com, they may have what you're looking for.