Carrier Gas Furnace, Pressure Switch Problems (Model 58MCA) CODE 31
Asked Dec 2, 2010, 09:18 AM
I have tried almost everything in my arsenal to try and diagnose the problem. First off I have a Carrier Gas Furnace that is almost 7 years old. Model 58MCA-80 (See attached photo for more information), with pressure switch #HK06NB123.
Intermittently I get a Red Flashing Code #31 when the unit tries to cycle. So far I have tried the following to fix
- Blown out the drain line
- Blown out each of the vacuum lines connected into the pressure switch
- Replaced the pressure switch with model HK06NB124 (Per my local Carrier Service Center), this did not fix the problem so I have since re-installed the existing old switch
- Electrically tested the pressure switch. I think I briefly got 25V when the unit called for air. I did this by touching my voltage meter to either electrical connector one the pressure switch itself.
- Jumped the pressure siwtch by connecting the yellow and orange wires. When jumped the unit will run correctly until I disconnect the wires.
- Checked both the exhaust and supply air piping.....all seems ok
- Inducer motor spins fine.....although I do not know how to test it to make sure it is spinning fast enough?
After all that I do have one random solution that will temporary let the unit work. If I disconnect the upper vacuum hose from the pressure switch (Attached photo with red arrow) while the unit first turns on, it will cycle and start burning gas like it should. I then reconnect the hose and everything is fine for the next 3-4 hours or so.
Let me know if you have any help for me! I am almost at the point of calling a service tech. to help me out.
Thanks in advanced!