Carrier 58MCA080 code 31

Old 01-26-16, 10:27 AM
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Carrier 58MCA080 code 31

Hello everyone!

We have a dual Carrier 58MCA080 setup in our home. We have been here roughly 8 yrs and furnaces came with the house.

Have had furnace servicing upper floor set code 31 (vent blockage) intermittently for several years. In the beginning it was once every year or two I would find furnace not producing heat. Turning the furnace off for a few minutes and then turning back on would take care of the issue.

About 2 yrs ago powering the furnace off would not resolve issue. Still setting code 31. Called heating company and they cleaned vents and replaced pressure switch.

Last year code returned. Heating company found golf ball in vent. They theorized golf ball had been there for long time (supported by brown discoloration/stain on ball) perhaps years. I thought finally we have gotten to the root of the issue.

This past weekend code 31 returns. Wanting to do a little checking myself before calling out for another service call I begin checking the issue myself. No signs of any blockages of inlet or outlet venting. Thought I'd try switching pressure switches between furnaces - no change. What I did discover was that leaving vacuum line off of furnace side of the switch results in furnace working. Further tweaking with the vacuum hose results in furnace running when vacuum line disconnected from either pressure switch or combustion air intake. Disconnecting same vacuum line from redundant gas valve turns burner off.

Any ideas?
Old 01-26-16, 11:09 AM
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Welcome to the forums.

Since that furnace can be mounted in several orientations..... the drain lines and the pressure switch lines need to be located in the proper locations.

You may also need to clean out the collector drain box and blow out all the vacuum lines.
The condensate lines may also need to be cleaned with the trap reprimed.

The manual is in the link below. I'm not familiar with this exact furnace so the reading is informative and detailed.

Equipment Manuals Integration/CRC3185.pdf

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