- Model Number
- CMPB075U3A
- Age
- More than 10 years
Attempted to start my furnace, and I noticed it's short-cycling this season. It starts up as usual, I can hear the burners fire up, and both the inducer motor and blower motor are spinning. Furnace is an old Ducane CMPB075U3A (20 years old) high-efficiency model.
Problem
Around 2 minutes after pumping out hot air, it shuts down, and the error light flashes 3 times (pressure switch open, should be closed).
What I've tried
For what it's worth, cooling still works just fine, although I feel like the blower output has been too weak in the last several years (but HVAC tech said it was fine when he replaced the AC 2 years ago).
Problem
Around 2 minutes after pumping out hot air, it shuts down, and the error light flashes 3 times (pressure switch open, should be closed).
What I've tried
- Replaced air filter
- Opened some additional vents
- Confirmed I'm able to manually spin the inducer motor without any resistance
- Confirmed the (single) pressure switch checks out with a DMM, and I can hear clicking when gently blowing into the tube
- Confirmed these tubes aren't clogged (there's one branch going to the burner area which I haven't taken apart yet)
- Confirmed condensation pump is in working order, and there are no clogs in the internal reservoir
For what it's worth, cooling still works just fine, although I feel like the blower output has been too weak in the last several years (but HVAC tech said it was fine when he replaced the AC 2 years ago).
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