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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Billy. I have a nordyne furnace. Had a pressure switch open

Customer Question

Hi Billy. I have a nordyne furnace. Had a pressure switch open code. Went to a local store and picked up a pressure switch. I installed it while I had the service panel open and had to hold the button to test it. Initially the unit ignited and stayed lit. I was very excited because before this it would night ignite, only the exhaust fan would come on. I let it run for about three minutes. The red light stayed on although the yellow light was blinking (low flame level sensor). I then took my hand off of the safety switch and the furnace shut off. I reinstalled the safety panel and went to turn on the furnace and am now getting the same error code of pressure switch open and no ignition. Any pointers?
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.

The pressure switches come in different pressure ranges, that is stamped on the pressure switch, generally between 1.75 and 2" water column .. look at your existing pressure switch tell me what it is rated at, then tell me what the new pressure switch is rated at.

We can go from there

Expert:  Phil replied 1 year ago.

Ooops. I mis typed, pressure range is 0.75 to 1.0" wc

Customer: replied 1 year ago.
I went to a local furnace supply store. Got the same pressure switch. Same part number. Both are stamped -1.74. Part number 632444
Expert:  Phil replied 1 year ago.


Please attach a well focused, close up photo of the wiring diagram glued inside the service panel, the picture needs to be taken from straight on, in very good light.

You can use the paper clip- icon at the right end of the tool bar at the top of this dialog box to attach it here.,Include a picture of the thermostat wire connections to the printed circuit board in the same area. Include a picture of the furnace taken from about 10 feet away with all of the furnace service panels removed so I can mark it up with instructions for you.

If you have an error code showing, tell me what the code read out is on the wiring diagram or a sticker next to the diagram please.

If there is no paper clip-icon, look for the '+attachfiles'link at left of your send button.

I can mark it up with trouble shooting instructions.

We can go from there.

Customer: replied 1 year ago.
Please see attached. Code is 2 blinks of red light
Customer: replied 1 year ago.
Please see attached
Expert:  Phil replied 1 year ago.


So far it sounds like a bad printed circuit card.

We can do a heat stress test on it.

Use a hair drier to slowly warm the printed circuit card up to120F or a bit warmer, but not over 140F... if there is any change in the error codes or other furnace behavior... the card has a cracked micro circuit that opens and closes as the card expands and contracts... that proves a bad printed circuit card.

No change however does not prove the card is good however... but a change proves the card is definitely bad.

Do not let the furnace run with the door closed and the pressure switch jumpered, this is only a test,