Carrier furnace won't heat, code 33


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Old 04-10-18, 05:13 PM
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Carrier furnace won't heat, code 33

Looking for any troubleshooting thoughts regarding my Carrier 58MCA060 furnace.

Symptoms:
  • The status light blinks 3 short, 3 long, which I understand is code 33 (limit switch). I pushed on the flame rollout switch without any effect. Ordered a new switch, just in case.
  • Filter was about 1 month old, so it was dirty but not so bad that it should have been restricting airflow.
  • The thermostat screen is blank, even though the wires are showing voltage with a multimeter. Tried replacing the thermostat, no improvement.
  • The blower for the house air is working, so there is power to the furnace, but the blower to circulate the burner air doesn't turn.
  • No indication that the burners are even trying to turn on.
  • Checked the condensation trap for a clog, flushed it out to be safe.
  • 3 amp fuse looks good, replaced it anyways to be safe.

Next step is probably going to be a call to a professional. Any thoughts on other things to check would be greatly appreciated.
 
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Old 04-10-18, 05:27 PM
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Welcome to the forums.

The burner will not fire with a code present.
Did you check for 24vac from R to C ?
If you don't have 24vac there.... the flame rollout sensor is tripped or the limit switch has not reset. You are interested in the limit circuit that connects pin 1 to pin 7.

Download this so you have it.... manuals online F9F9a827d0f-517a-40fd.pdf

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Last edited by PJmax; 04-10-18 at 05:56 PM.
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Old 04-11-18, 03:58 PM
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It ended up being the original cheap thermostat that went bad. The newer thermostat required a C wire, which was terminated on the thermostat side but I didn't notice it was not terminated at the furnace until I was investigating the circuit.

Thanks for the feedback!
 
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Old 04-11-18, 05:49 PM
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So what caused the limit switch fault?
 
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Old 04-12-18, 02:21 AM
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No idea. The rollout switch was not popped out, but maybe it had also gone bad? It's possible that both the switch and thermostat needed replacing, although the chances of 2 pieces of hardware failing at the same time is pretty slim.
 
 

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