Furnace Short Cycles Off and On
I have a Suburban SF30fq furnace that cycles the heater flame off and on about every three minutes while the coach is reaching the thermostat setting (technically called short cycling on the limit swi...
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If the motor is running very much slow, the combustion air would be insufficient to activate the sail switch and the furnace would not light at all. The two fans are run by the same motor on the same shaft in RV furnaces. Getting insufficient airflow on the duct side but not the combustion side would imply some physical problem with that fan rather than a motor problem, and typically such damage would be rather obvious.
Looking at the documentation for the furnace, the limit switch and the sail switch are wired in series. It might be worthwhile to check that the sail switch is behaving properly. Depending on how one is checking the limit switch, the sail switch opening may appear to be the limit switch opening. Follow Doug's advice first before checking the sail switch as he has far, far more experience and knowledge than I have.
Looking at the documentation for the furnace, the limit switch and the sail switch are wired in series. It might be worthwhile to check that the sail switch is behaving properly. Depending on how one is checking the limit switch, the sail switch opening may appear to be the limit switch opening. Follow Doug's advice first before checking the sail switch as he has far, far more experience and knowledge than I have.
