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the Musigician
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hi and welcome to the forum. i'd look in the direction of the switch first. cut the power first and check the hoses for debris or water. blow in and out to see if it's working. turn power back on, check for 24v at the switch.

DM
 

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Hvac Pro
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The pressure switch you have is -.50"WC and that Lennox (actually AireFlo one) is -.40 "and the wrong one. I doubt if it is the pressure switch as usually you only get one failed part at a time. Tridelta has gone out of business, Honeywell makes most of them now. Probably have to get it from Trane due to the mounting bracket etc. The yellow part on the board is burnt. I would NEVER buy parts on EBAY as it may be used/faulty. My cost on those boards is at least $150 so you won't get it cheaper and be new. Buyer beware.
 

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Very strange for both the draft inducer pressure switch to go bad and the control board to short out. In the board picture it looks like a disc capacitor but is more than likely a MOV suppressor - did your circuit breaker trip? depending where the surge came from the board may still be good, try clipping the MOV out of the circuit and resetting the breaker. They are only a dollar and if proved can be replaced later.

The control board must see that pressure switch initially open before starting the sequence then closed after the fan starts - this is so you can't trick it with a jumper wire. After seeing the board I doubt its bad.

And as DM said make sure your lines are clear on the switch.
 

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Discussion Starter · #6 · (Edited)
Thank you for your suggestions!

The control board was "burnt" as you see on the picture for 4 years. It was recommended to get it replaced, but I never bothered with it as everything was working fine until recently.

Repair man did some tests, like blowing into a tube to check if it "clicks" and plugging blower wire directly to a switch to check if the fan is working.

The result: Blower didn't "click", but the fan was working.

So his assumption that the control board gone bad finally along with a pressure switch, but since he wasn't sure I did not want to pay the price only to find later something else has gone bad. So, I will try to replace control board first before I replace pressure switch.

I am bit hesitant to clip something of the board though. I would rather try another board.

Luckily, the weather finally starting to get warmer, so I can go by without furnace for a while.
 

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Apparently, the tech can't afford a manometer.
 

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Discussion Starter · #9 ·
So my current concerns are... Is Control board simply plug & play? and... I heard someone mentioned that pressure switch might need cleaning. Will it help?
 

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Very strange for both the draft inducer pressure switch to go bad and the control board to short out. In the board picture it looks like a disc capacitor but is more than likely a MOV suppressor - did your circuit breaker trip? depending where the surge came from the board may still be good, try clipping the MOV out of the circuit and resetting the breaker. They are only a dollar and if proved can be replaced later.

The control board must see that pressure switch initially open before starting the sequence then closed after the fan starts - this is so you can't trick it with a jumper wire. After seeing the board I doubt its bad.

And as DM said make sure your lines are clear on the switch.
You replace any electronics on that board and you will void any homeowners policy you own.

The boards are safety lab certified as a whole component. Any damage occurring to home traceable to furnace would not be covered.

If the boards were meant to be repaired outside lab conditions there would be a market for recycled boards. Most tech have the know how to repair a board but have the good sense not to.
 

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HVAC / Plumbing
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1,801 Posts
Probably just indicating power to the unit. Usually count # of blinks & look on the back of the blower door for the code
 

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Discussion Starter · #15 · (Edited)
Normal. No call for heat.

Just a note that there is a manual switch to run just the fan for fresh air intake and if connected directly to switch fan works, but when connected through control board as normal it will not work. Does this suggest that control board is actually faulty?
 

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HVAC / Plumbing
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If you have a V M you could check for 110 v at the red terminal on the board on a call for heat..Red from V M to red wire terminal.. black lead from V M to ground or white.. If you have 110 v the fan should run
 

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that's hilarious, thanks - grins back at ya :)
Contact the mfg of any HVAC brand. They'll confirm what I told you.

Controls are not rebuilt for a darn good reason. When a new furnace model is safety certified it is with the components that the mfg hast designed in to it.

Any field alterations would be considered a deviation (that means repairing a board or any other part of the safety or ignition system) from the original design and puts the liability squarely on the shoulder of the offending individual.

There was a guy around here who was repairing Bryant blower boards some years ago for local wholesaler. UTS shut 'em down hard. And rightfully so.

The solid state components were generic and not the same quality the OEM put into to the board. There were a few cases of gas valves not closing on the end of a cycle.
I ran those calls and they were the repaired boards I mentioned.
 

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HVAC / Plumbing
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Contact the mfg of any HVAC brand. They'll confirm what I told you.

Controls are not rebuilt for a darn good reason. When a new furnace model is safety certified it is with the components that the mfg hast designed in to it.

Any field alterations would be considered a deviation (that means repairing a board or any other part of the safety or ignition system) from the original design and puts the liability squarely on the shoulder of the offending individual.

There was a guy around here who was repairing Bryant blower boards some years ago for local wholesaler. UTS shut 'em down hard. And rightfully so.

The solid state components were generic and not the same quality the OEM put into to the board. There were a few cases of gas valves not closing on the end of a cycle.
I ran those calls and they were the repaired boards I mentioned.



I agree... Wouldn't buy parts off E-Bay either
 

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Hvac Pro
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The other issue no one seems to understand or care about is that a circuit board is a critical safety device. If you mess it up and the flame sensor/flame failure part of it quits you can fill up the furnace/house with gas and voila, first person to turn on a light switch blows up the house. Nothing against some DIY repairs but fixing circuit boards is verboten.
 
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