Trane furnace model TUE120A960L3 pressure switches error. I followed the recommended troubleshooting steps and determined that the pressure switch was operating OK, the inducer fan checked OK, vent piping is clear, etc. after furnace runs its heat cycle and thermostat stops calling for heat, the IFC board shows a slow blinking pattern-normal no heat called for. When thermostat later calls for heat the IFC board begins giving the 3 blinking light pattern- code for pressure switch error. If I remove the vacuum line running from pressure switch to the fitting on the burn box/inducer fan assembly and then immediately reconnect it, the error code on the IFC changes to the normal quick flashing pattern- call for heat the furnace then fires up in proper sequence and runs a normal cycle then the same old thing repeats for the next cycle. If anyone has a suggestion or any information related to this problem I'd sure be grateful.

Added information: This furnace is operates on natural gas.

I would change out the motherboard control module, this is the problem (common) that I run into and this repair always does this trick!

Hope this helps!
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