No 12V Power to Thermostat

[hfreaves]

I've an '02 27' Mako. Tried the furnace for the first time this season (just bought it) .... no furnace start. Switched back to A/C (worked fine up to now) and no operation whatsoever. Got the manual on the PC board thermostt, followed the troubleshooting guide. Found no 2V at the upper unit control panel. Checked the 12V supply to the thermostat - found no 12V power. The A/C mfg recommends a fuse between the main fuse panel and the thermostat. Does anyone have any idea where that fuse might be? Other recommendations on how to 'restore 12V to the thermostat' (as the troubleshooting guide puts so succinctly)? (Where does the 12V supply wire to the thermostat come from (other than 'overhead)?

[bob3nliz]

I have over head A/C. When I take filter out to clean I see a metal box with a cover plate being held with a screw, under it I see 110 wires and 12V wires there also is a 12V fuse in there. I do not know where the 12V supply wire comes from and not even sure this will help you. :) Bob

[Timothy]

check your fuse panel, it would have to come off of the battery as the furnace works without 120 VAC. The box suggested in the post above may contain a fuse too, there could be 12V feed from the furnace itself.

[hfreaves]

Timothy (and all),
Thanks for the response. It turns out the 12V to the thermostat is routed through the PC board controlling the furnace, and the 12V wire to that board was loose. (I think I may have pulled on that wire getting some kitchen tools out from behind the drawer, just over the furnace.) Re- seating the supply wire terminal and turning the external furnace switch to 'ON" solved the problem. I've since connected the 12V feed to the thermostat directly to the 12V feed to the furnace, so that the furnace swith position has no effect on the A/C contol by the thermostat.

Thanks again, all.

[AyeZer]

It is good to hear that the problem about the thermostat is already solved. The thread should not be deleted for future references of people who will encounter the same problem like mine. PC boards of electrical appliances are really hard to understand sometimes.



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