I have a tempstar 9MPT model based furnace. Also sold under a number of other brands - comfort air, etc. It is a two stage heating with a PSC motor high efficiency furnace. After about 7 minutes of running, instead of cycling to high fan speed and BTU output, it restarts going through the pre-blower cycle before re-engaging the blower.

Any idea where to start troubleshooting this?


1 Answer 1


I blew out (by mouth) the rubber line coming back from the low pressure vacuum switch back to furnace near the drain. It initially had some resistance but then cleared. Everything worked fine after that.

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