Furnace failure

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Old 01-08-09, 10:17 PM
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Furnace failure

I have a Carrier 58MXA060-12 gas furnace. I had the heat exchangers changed out on the class action law suit 1 year ago. Now the furnace has been cutting out leaving the blower motor running. Error code I am getting is 33. I assumed it was the pressure switch, I cleared the drain lines and it ran for a couple of days. Once it failed again I turned off the power for a couple of minutes to a couple of hours, each time I power the unit up the error code comes back immediatly before even testing the system.
How do I clear the codes if cutting the power will not work? Bad control board?
Any clues or suggestions would be welcome?
 
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Old 01-09-09, 01:35 AM
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The 33 error code identifies an open limir switch or flame rollout switch or fusible link.

You need to use a multimeter to trace the 24 VAC signal through these switches to find the open switch or fusible link.

The circuit diagram should identify which pins on the ignition module begin and end this circuit, and the limit switch should be readily available to test the voltage.

If the burner operates at all, it's probably not the flame rollout/fusible links.

You need to describe what is happening when you turn the thermostat up in more detail --- your description is somewhat vague.
 
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Old 01-09-09, 07:07 AM
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When I say turning the power off, I mean turning off the 110V switch, the thermostat set to always calling for heat.

The first 3 or 4 times the furnace failed when I turned off the power completely, checked vents once, cleared condensate lines the second, etc. Each time I restarted the furnace it would run for a day or so then stop heating and produced the error code 33.

Now when I turn off the power and turn it back on, the blower starts the purge cycle and the error code comes up immediately, preventing the burner from lighting. I thought once you turned the power off and on the code would clear until the furnace went through the purge cycle.

If I interperet what you are saying correctly, an immediate error would be normal if one of the swithes is stuck open not completing the 24V circuit. I checked the pressure switch which is good (this was my orginal assumption that I had a pressure problem). Second thought just occured to me, could this be a result of a bad 24V power supply?
 
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Old 01-09-09, 09:33 AM
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If you had no 24VAC the ignition module wouldn't work at all (no error light).


I'd trace out that circuit from the limit switch --- it probably goes to one or more flame rollout switches. Check to see if the 24VAC has continuit across those switches or whether the voltage stops there --- which would probably be the reason why the furnace wont run.

Flame rollout switches may be reseattable or may be fusible links that would need to be replaced.

If the FRS are open, the more important issue is WHY these switches opened --- usually for important safety reasons. If that's the case we need to talk more about that issue.
 
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