Trane rtu with ddc – no heating no draft motor

Am wondering if anyone has dealt with an issue where the Trane rtu yhc048 will not cycle on the heating during auto cycle test (or at any other time) due to the venter motor contacts not closing in the ignition control board? I checked all the burner high temp limit switches and for continuity in the wiring, switched with a known working ignition control board, as well as a working main control board with no success. Seems really odd when known working main board and ign control boards do not work in this unit while all other test functions work in the auto cycle, the unit worked exactly the same before and after swapping the boards. The venter motor works fine when voltage is applied. Am wondering if it may have anything to do with the Lon talk board interfering… But I would think for the auto cycle test it shouldn\’t. The Lon board appears ok by the way the lights are blinking although I haven\’t tested it beyond that.

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