I've got a limt switch acting odd, on an old York.
If the thermostat has the fan forced on high (by setting it to the ON position), then the furnace runs fine.
If the thermostat has the fan set to AUTO, then something odd happes... the cold system goes through the cycle and starts to heat up. When the limit switch heat upto the 1st setting (the fan off), instead of doing nothing it kills the flame (as if it had hit the limit... but it is far from it). There is an assist heater on the limit switch, fyi.
There is some life in the AUTO setting... if the system is partially heated (sitting just above the fan "OFF" point on the limit switch... then if the thermostat calls for heat and I have the fan in the AUTO it will ignite, heat up to the fan ON (which actually does turn the fan on)... heat until the thermostat says to turn off and then the fan continue to blow until the limit switch gets down to the 'off' setting, just as it should.
Starting temp above fan OFF works fine. Starting temp below fan OFF kills the flame as it heats up.
bad limit switch? bad relay? wire short in the limt switch?