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I woke up one morning to a horrendous noise from my furnace. It turns out that the fan inside the combustion blower broke apart (it was plastic). I replaced it with a new fan assembly made of steel. Seems to be getting good suction...I check for air flow on the outside vent.

The problem now is the igniter element is not heating up. The control board is blinking 3 flashes - which decodes to pressure switch stuck open. When I suck on the combustion side of the switch briefly the heating element will glow and eventually the gas comes on. So, I thought I had a bad pressure switch. I just ordered a new pressure switch, and no luck. Still 3 blinking lights and no heat.

I tested to see if the pressure switch was getting any voltage from the control board and nothing. Could it be the control board? I just wanted to see if that may sound to be the culprit, as the control board is not a 25$ part

ps. model number: P3URD12N07501A

The pressure switch should have 24vac to ground at one side and at both sides once it closes.


Look at wiring diagram to see if the circuit goes through any other components between board and switch.



What is brand of furnace and is it in a mobile home ?




Thanks,
Robert

Hi, thanks for the reply!

My unit is a York, its in a home, not mobile.

No voltage. But, I do find that when I touch the common and the "ON" leads on the pressure switch, the heating element does begin to glow and the gas starts up after several seconds...any thoughts?

Hi,

What do you mean by "when I touch" ?

By replacing fan blade with a non oem blade, you may have altered the pressure required to close the switch.


I do not have a wiring diagram for your furnace, can you send one to my email ?


robert@mobilehomerepair.com


Thanks,
Robert

Hi,

You are jumping the pressure switch which means you are getting power to the switch.

You're also getting it to the ignitor when the pressure switch is jumpered.


With a new switch, the problem most likely lies in getting correct water column pressure at switch.


This involves the motor/fan, vent piping, tubes connecting the motor and switch.


If tubes are tight, unkinked, unclogged and vent pipe is clear, straight and securely attached, then look at motor.


IF motor appears to be running good, the fan may be the problem as it is different and that can change the specs of operation.


Only way to know for sure would be to test water column pressure at switch to see if the motor was reaching design specs to close switch.


Thanks,
Robert

Excellent info. I really appreciate the advice. I will check the water column pressure to see if the new fan is pulling enough air. Thanks again!

You're very welcome, your owners manual and possibly the switch will say what w.c. pressure should be to close contacts.



Thanks,
Robert