Gas Furnace does not see closed pressure switch


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Old 10-09-22, 01:25 PM
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Gas Furnace does not see closed pressure switch

Hello guys,

I have a gas furnace, and when I turned it on initially, it gave me a two blink code specifying that the pressure switches stuck closed.

Iíve tested everything, including the switch with a multimeter, checked the hose, check the wiring from the switch all the way back to the control board and everything seems to be working as it should be, but the second I set the thermostat to heat. It gives me that two blink code.

I verified that the vent outside is free of obstruction and I donít see anything in the intake port on the roof.

I went as far as to replace the switch, and it still is doing the exact same thing.

I do hear the switch audibly click when I start the furnace up.

The only thing left that I can think of is the control board, but is there anyway to verify this that you guys are aware of?

Thanks for the help and I apologize if I am asking a commonly asked question, but Iíve done 1 million searches, and I cannot find the resolution.
 
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Old 10-09-22, 02:31 PM
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Welcome to the forums.

Connect a meter on the AC setting for 24v across the pressure switch.
You need to see 24vac with the furnace not running.
Do you see that ?
 
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Old 10-09-22, 03:03 PM
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To confirm:

Are you saying 24v with the thermostat not calling for heat or with the power to the furnace off.

I assume you mean with no call for heat - Iím checking that now
 
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Old 10-09-22, 03:23 PM
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With no call for heat but it Ďrunningí (fan sound but the thermostat set for no ac or heat) I get:

0.257V on each terminal (using a ground)

0.00V if I connect the probes to each terminal.

When I turn the thermostat to call for heat, it shows 28V on both terminalís separately
 
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Old 10-09-22, 04:18 PM
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Not to ground..... across the switch.

Most furnace keep 24v on the safety loop at all time.
It sounds like yours does not. That means on a call for heat.....before the inducer runs.... you should be measuring 24v. When the inducer starts you measure 0v.

24v would mean open switch and 0v would mean closed switch.
 
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Old 10-09-22, 04:47 PM
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From terminal to terminal I get 0v.

I do hear a motor when I first power it on. I thought that was the inducer motor?

I do hear an audible click then the furnace is powered on and the fan kicks on. This is clearly from the pressure switch.

 
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Old 10-10-22, 07:09 PM
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Tested again

current error: 2 blinks: Closed pressure switch
(only starts blinking after a call for heat)

Before call for heat: 0V across the pressure switch terminals

after call for hear: 0V across the pressure switch terminals

With the multimeter connected to a ground:

before call for heat: 28.1V from the first wire
0v on the second wire

after call for heat: 28.1V on both wires
 
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Old 10-10-22, 08:27 PM
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Possible solution

I found that the inducer motor should not be running continuously when there is no call for heat.

My inducer motor turns on right away when I turn the panel to the furnace back on.

Everything I am reading is saying that this is a control board problem.

Thoughts?
 
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Old 10-13-22, 04:20 PM
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Issue resolved

Replaced the board - issue resolved.

thank you guys for the advice
 
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Old 10-13-22, 07:10 PM
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Good job. Thanks for letting us know how you made out.
 
 

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