Honeywell Chronotherm IV, fan set on AUTO, runs randomly.

The only suggestion I have on this is to check the red and green wires and insuation for bare spots to be sure they are not in contact with each other at times. The red wire should be 24 volts and the green wire goes to the fan relay. I have seen this happen before, the wires touch due to stripped insulation and when the fan cycles on they seperate.
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