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I have a Trane hot air furnace that has recently become temperamental with freezing rain or snow contaminating the air supply. Can humidity in the air supply interfere with its operation? In new England, we usually have very cold and dry weather, the only common element here seems to be the wetness.

The flash code is three rapid flashes. It is described by Trane's documentation as "Pressure switch problem — Blockage in vent, condensate drain plugged, etc."

I checked the air intake, and it was never blocked, from the outside anyway. Twice this season the furnace would not start until the bad weather stopped, then it resumed operation on its own.

I am thinking something is causing condensation to freeze in one of the two venting pipes. Perhaps getting an endoscope to look down the 10' of pipe...

Any suggestions and ideas welcome.

0xF2
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    You also mentioned condensate that is a liquid water drain if a closed combustion fire box. If the drain is frozen it will shutdown to prevent the water from damaging things. – Ed Beal Mar 13 '22 at 20:23
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    If the furnace is in a cold location (I have one in my unheated attic) then the condensate drain line can freeze and cause the furnace to shut down. There could be a drain plug on the side of the furnace you can open and let the water out (or see the ice, as the case may be) (Be sure to have a bucket handy first though.) – Duston Mar 14 '22 at 13:36
  • Checking the condensate line was unfruitful. In the end, the resolution was calling in a technician, who replaced the pressure switch and (aha!) a capacitor that had gone bad with age. – 0xF2 Sep 20 '22 at 08:23

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