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HVAC Issue

NTxAg

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Joined
Nov 10, 2015
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33
Location
Tyler, TX
So last Thursday the fan in my HVAC unit stops working. Thermostat shows the fan as on and the cool setting is on. My outside unit is working it *** off, frosting up, but no air is coming through the vents in the house. I shut it down and call the HVAC company I used on another project. Tech comes out say the relay switch on the board is fried and I have to get a new board since they are all one part. He makes some calls and no one in town has one so it has to be ordered, won't be here until Monday or Tuesday. He say he will hook up a jumper that will let the fan run so the house can cool down, but that even when the AC stops the fan will still run. No problem.

Fast forward to today, I haven't heard from the company so I give them a call at 430. Nice lady that answered the phone said that the tech notes show that they came back the same day and fixed the problem. She didn't realize I haven't had heat or AC since Thursday. It has dipped down in to the low 40s and up to the mid 80s in the last five days but it hasn't been too uncomfortable.

She swears she will find out what is going on.

I decide to take a look myself, I find the board in question, snap some pictures and head to the internet. The board will cost me $135 to have it here by Friday. They quoted me $500 to do the work.

My question is this, how hard is it to change the board? The part # is CNT03076. I took extensive photos of my current board and this board is marked the exact same.

I have never worked on an HVAC unit before, but have some minimal handyman knowledge and have built many a computer front scratch so I have been around computer boards. It looks really simple, unscrew a few terminals, put wire in terminals with the same markings on new board, tighten screws, plug in two harnesses, then hook up the remaining blade terminated wires to the right posts.

Am I missing something? Is there another part I have to worry about frying if I do this wrong? Is there a capacitor I am missing that may discharge into my body? I can't see a reason not to tell them to take a hike given their screw up and save myself almost $380 bucks.

The whole damn unit is original to the house, so 17 years old, seems like I am probably going to have to replace it soon anyway so why not try myself.

Justin


Sorry if some of the terminology is wrong.
 
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bonneyman

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Desert SW
If you possess minimum skills you can do it. Two molex connectors on the board, and the plugs can't be put on wrong. They only go on one way.
The 5 t-stat wire terminals along the bottom are marked C,R,W, Y, and G - match them wire to wire from the old board. The remaining wires just take off the old board one at a time and hook them up to the corresponding terminal on the new board. Sometimes they are in the same configuration, sometimes not.

But I'd be suspect. Many times the relays on the boards go out because of some problem outside the board. Blower motor relays are small contacts, relatively low amp rating. If the motor hangs up, has tight bearings, drags a little, is clogged, etc it's amps use goes up and that type of abuse will take out a board relay quickly. Not solving the root problem could make the new board fail too,
 

Bronson

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Aug 2, 2011
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12,680
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Texas panhandle
Is the blower motor original to the unit?
If so, replace it along with the board.
Not to be a smart-***, but be sure to UNPLUG the unit before You start working on it.
 
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NTxAg

Active member
Joined
Nov 10, 2015
Messages
33
Location
Tyler, TX
Is the blower motor original to the unit?
If so, replace it along with the board.
Not to be a smart-***, but be sure to UNPLUG the unit before You start working on it.
Yes it is.

Yeah, I am going to have to unplug it so I can hook up a work light.

I did read on an HVAC site where these model boards were well known for blowing relays back when they were common, the early 2000s.

I found a decent tutorial on allthumbsdiy.com. Like I said, seems pretty straight forward for all of it.

Thanks y'all for the advice!

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mygarageone

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Oct 16, 2013
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Munising , Mich
If you possess minimum skills you can do it. Two molex connectors on the board, and the plugs can't be put on wrong. They only go on one way.
The 5 t-stat wire terminals along the bottom are marked C,R,W, Y, and G - match them wire to wire from the old board. The remaining wires just take off the old board one at a time and hook them up to the corresponding terminal on the new board. Sometimes they are in the same configuration, sometimes not.

But I'd be suspect. Many times the relays on the boards go out because of some problem outside the board. Blower motor relays are small contacts, relatively low amp rating. If the motor hangs up, has tight bearings, drags a little, is clogged, etc it's amps use goes up and that type of abuse will take out a board relay quickly. Not solving the root problem could make the new board fail too,
It's a 17 yr unit , at that age it's not uncommon to fail .
 

LS6 Tommy

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Dec 27, 2013
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26,162
Location
Northern NJ
All the advice above is spot on. I still don't know why I keep reading about permanent HVAC units that "plug in". It just ain't right...:lol_hitti

Tommy
 
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Stuff

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Aug 31, 2013
Messages
572
I agree that they are not hard to replace. Take lots of pictures beforehand. If you have a label maker that can help as well.

I see that this one has three dip switches. Some of the replacement boards don't have the same function so double check. The new board should come with a cheat sheet saying what the switches are. Find out on your old system what the switches were set to and what they mean.
 
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NTxAg

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Nov 10, 2015
Messages
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Location
Tyler, TX
I hate it when an author abandons the thread before the story is finished so, here I am. Got the part in Friday, two days after I ordered it. I thought to check the time before I went I to the attic so I could see how long it took. Transfered over the thermo wires and the two molex plugs then the last few terminated wires. Got back down from the attic. IT TOOK ME 7 MINUTES!

they wanted $535 for a 90 dollar part, 1 hour service call to check what was wrong and a return trip that would have taken 7 minutes once they got here.

Some notes, the board was the exact same so the dip switches weren't an issue. The fan motor wasn't original, there were no metal shavings or noise when the fan turned so I opted not to replace it. I might regret it but with oil at $35/bbl and work sparse I made the judgement call to save the money.

Thank y'all for all y'alls help!

Justin

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NTxAg

Active member
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Nov 10, 2015
Messages
33
Location
Tyler, TX
All the advice above is spot on. I still don't know why I keep reading about permanent HVAC units that "plug in". It just ain't right...:lol_hitti

Tommy
I guess I don't get the humor here? Are they supposed to be hard wired?

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