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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 21532
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I have a comfortmaker C9MPD050F12A3 furnace that works

Customer Question

I have a comfortmaker C9MPD050F12A3 furnace that works properly until the main blower energizes. The main burner shuts down almost immediately after the blower comes on.
JA: Did you check the furnace's filters?
Customer: Yes
JA: Do you plan on doing the work yourself?
Customer: Yes. I cleaned the flame sensor, checked the rollout switches and pressure switcheck.
JA: Anything else we should know to help you best?
Customer: No. I checked for obstructions in the inlet and outlet pipe. The only thing I have found so far is the gasket behind the inducer motor appears to be deteriorating.
Submitted: 9 months ago.
Category: HVAC
Expert:  Rick replied 9 months ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can continue our conversation.

If the main burner flame distorts at all you could have a cracked heat exchanger. Also check the combustion condensate drain piping and trap for blockages. Slime accumulation in the drain or trap can block condensate flow causing a shut down.

Customer: replied 9 months ago.
The main burner looks fine nice and blue. The problem is it shuts off when the main blower activates. I did replace a drain hose. I also primed the trap. Would a cracked gasket behind the inducer motor housing cause this problem?
Expert:  Rick replied 9 months ago.

If the gasket was the primary cause the unit probably wouldn't fire up. What are you getting for a flash sequence on the control board when it locks out?

Customer: replied 9 months ago.
Normal heartbeat
Expert:  Rick replied 9 months ago.

Does it restart on its own or do you have to cycle the power?

Customer: replied 9 months ago.
Usually cycling the power
Expert:  Rick replied 9 months ago.

You should only have to cycle the power if you have a lockout and you're saying the board blinks normal operation, no lockout code. This makes me suspect the board. A bad connection is another possibility.

Customer: replied 9 months ago.
This unit only has the gas valve diagnostic light. There are no lights on the board itself. The timing of everything appears normal. I even did a test from the manual to check the ignitor sequence with and without the gas supply.
It was perfect.
Expert:  Rick replied 9 months ago.

The shutdown occurs after the ignition sequence is finished. My service manual doesn't indicate this model has a Smart Valve. If that's what you have then the Smart Valve not the board would be suspect.

Expert:  Rick replied 9 months ago.

I have to step away for about an hour. If you have more question I'll respond when I return.

Customer: replied 9 months ago.
It has a Honeywell SV9541 Gas valve
Customer: replied 9 months ago.
Expert:  Rick replied 9 months ago.

That's a Smart Valve

Customer: replied 9 months ago.
OK thanks I will try some things.
Expert:  Rick replied 9 months ago.

You're welcome