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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22677
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Carrier Furnace flashing LED code 31: Pressure Draft Safeguard Aux-Lim

Resolved Question:

my Carrier Furnace is flashing an LED code 31: Pressure Draft Safeguard Aux-Limit...inducer motor and blower motor seem to be working...what could the problem be?
Submitted: 7 years ago.
Category: HVAC
Customer: replied 7 years ago.
I haven't tried to replace any parts yet. Truth is, I can't find the model number of the furnace. There is a Model and Serial No. tag on the airconditioning unit above, but nothing on the furnace....Without knowing the model of the unit, if there is anything you can do to help me fix it, I would be greatly appreciative.
Expert:  BillyHvac replied 7 years ago.
Ok, you are on the right track. First thing we want to do is bypass the pressure switch. First so we can go at a comfortable pace, do ou know where the pressure switch is?
Customer: replied 7 years ago.
no idea where the pressure switch is.
Expert:  BillyHvac replied 7 years ago.

There is a draft fan in the upper section attached to vent pipe. Then you will see a rubber tube as thick as a pencil, this runs from the furnace to a small pie shaped switch with 2 wires attached. ill look like the switch at this link.

Customer: replied 7 years ago.
I will find it. Is the draft fan, the same thing as an inducer motor? If so, the switch which is a rectangular piece, with two wires coming off of it is screwed to the furnace behind and to the left of the wheel on what I have been thinking is the inducer motor.
Expert:  BillyHvac replied 7 years ago.

The exhaust fan is the inducer motor. The rectangle behind the gas valve with 2 wires is the limit. We will be checking that also. To test the pressure switch...

remove the 2 wire from the switch (not the limit) hold them apart, start furnace, when inducer fan kicks on touch them together so the metal ends touch and hold them that way. See if unit progresses

Customer: replied 7 years ago.
I will be following these steps tonight after work, This is good info. once the inducer kicks on, I will hold the wires together. Go ahead and give me the entire procedure and I will follow it when I get home.
Expert:  BillyHvac replied 7 years ago.

If the unit ignites when the 2 wires are touched = cracked rubber hose, plugged nipple port where the tube attaches, plugged vent, bad pressure switch.

If it does not change the code and we still are at same fault, look around burner area for dime sized switches with little reset buttons in the center. Also remove the 2 wires from the limit switch on the rectangle plate and attach together so metal ends touch. Then let me know what has happened. I will be online tonight

BillyHvac and 2 other HVAC Specialists are ready to help you
Customer: replied 7 years ago.

Thanks for the information. I was not able to work on my furnace last night. it was running just fine. I will wait for it to fail again to run the tests. There is a storm coming in this weekend and temps will drop. The way things are going right now, it will probably fail when I need it most. Luckily, I have two furnaces that heat my house so it won't be quite so bad. I will let you know how it goes.