Carrier 58MCA long igniter warm-up time

davetab

My Carrier 58 MCA has an abnormally long igniter warm-up time. Here's what happens: The thermostat calls for heat - the furnace starts working, churning, sometimes for 30 minutes without a call for gas...then it calls for gas, it lights, hot air blows for 2-3 minutes then shuts off. The furnace immediately starts working again, churning again for a short time, then, it calls for gas, it lights, and hot air blows for as long as it takes to give the thermostat what it wants. This is a high efficiency set-up, it just seems terribly inefficient to me - any ideas?

NiNe O

check voltage across the pressure switch. Sounds like there may be a blockage of some sort somewhere.

davetab

I wouldn't quite know how to do that - where would the blockage likely (or possibly be) and how would a person a) check it, b) clear it?

NiNe O

It could be in the flue pipe intake or exhaust, in the pressure switch tubing, in the pressure switch, in the condensate collection box, in the condensate piping, in the condensate trap. But I would check the voltage across the pressure switch before checking any of them. If you have a voltage meter it is pretty easy to do.

HVACTECH96

Check diagnostic light to see if any codes come up during long start up time.Probably get a code 31 .Move the wires on press switch alittle.If problem clears up, replace pressure switch because older metal ones commonly fail on this unit due to vibration of ID motor.

davetab

I'll check it - I suppose the proper voltage is noted in the owner's manual. If it's too low it will indicate a blockage? I would be fairly confident to disconnect hoses and check for debris - I don't see myself getting too invasive. I've earned my diy stripes...but, I worry about messing with the gas - my kids sleep here:.)

davetab

Now that's my kind of advice - jiggling wires! Definitely within my skill set. Will do. Thank you!

NiNe O

with voltmeter set to ac and your leads one on each terminal of the switch. small motor in burner compartment will spin and there should be no voltage reading if furnace is working correctly. This means switch is closed and there is no potential difference across the switch. it that little motor is spinning and you see 24 volts (give or take a couple volts) then you have a blockage somewhere.

davetab

Thank you for the clear, step by step directions with possible outcomes - very kind of you.
I'll do it first thing tomorrow.

davetab

OK, I jiggled some wires and did a error code check: as predicted by you fellas, it's a code 31. I don't have a voltometer: If I were to first try clearing any potential blockages...using the attached photo to point me in the right direction, where would I start? I busted out the schematic to find out how to do the code check....
I can try and find the various tubes....but would appreciate some guidance.
Is this risky business? Or, is it just a matter of un-doing a tube, shaking it out and re-connecting?
And, I noticed some moisture as seen in the more close-up photo. Is this a sign of something?

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HVACTECH96

Looks like you have a plugged condensate trap.The white thing with hoses going to it.Best way to clean it is remove and flush with hot water.You could try and blow it out if you have compressor.Have towel ready because there will probably be alot of water coming out of larger rubber hose when you pull it off trap.

HVACTECH96

One other thing, secondary HE fills with water and causes pressure switch to not close which gives you a code 31 and alot off times water leaking from behind inducer motor.

davetab

Ok, I'll get some towels, power down, remove the white thing and clean it out. I don't know what secondary HE means...

HVACTECH96

Secondary Heat Exchanger, its what that motor and slinky rubber hose is attached to.

davetab

I got it, heat exchanger. It's labeled as "inside"....does that mean inside the inducer assembly and I would need to remove a bunch of stuff?