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c5pilot 02-21-2008 04:01 PM

Carrier 58MXA pressure problem
I graduated oil burner tech school MANY years ago and am technically minded. I don't have too much experience with gas but did do a little tech work a few years ago.

I own a 10 year old Carrier 58MXA 90% furnace. I replaced the control center exactly 2 years ago (bad circuit unless I applied pressure on the board)... I was a computer tech too ;). This year I'm getting an intermittent 3-1 error. I blew out the trap and flushed it with water, cleaned all the vents with a paper clip, and checked all the tubes and hoses. The pressure switch would only pull out about half way and since I get parts for cost I replaced that just to be sure. It worked for 2 weeks straight.

Now it's acting up again. I've noticed I can get the igniter to energize if I disconnect the pressure tube from the gas valve and combustion air. It will run through a full cycle and intermittently fails again.

What am I missing? Where else can I get a clog that prevents the pressure switch from making? Thanks, Joe.

HvacWiz 02-21-2008 05:14 PM

Just guessing on this one, but your secondary heat exchanger could be plugged up.

c5pilot 02-21-2008 08:30 PM

Are there any instructions available that explain the correct way to check it out? Does it get blocked with condensation buildup or debris carried from outside? Thanks for the quick response.

Anyone else have any clues?

c5pilot 02-22-2008 07:32 PM

OK, I think I have this figured out. I went to get a couple of fernco couplings so I could disconnect the inlet pipe from the combustion area. Turned out the pipe didn't go in as far as I thought and was able to slide it far enough without cutting.

I found a leaf against the screen.

So far, everything is working smoothly. Now I have a spare pressure switch if my neighbors ever need one. All the outlets, tubing, and trap have been serviced, and I gained more knowledge solving something myself.

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