Furn/A/C Wiring ? pls help troubleshoot
I installed a new furnace last winter, and was working last night on hooking up the a/c. The furnace is wired properly and ran fine through the heating season. I didn’t have a condensate pan installed (horizontal app) so I left the condenser wiring unhooked until I got the pan in. Anyway, I’m not super familiar with wiring HVAC and wonder:
My problem is either the thermostat not making contact properly with its sub base, or a safety switch in the furnace is tripped. I would like to jump the thermostat (24 vac) wiring at the furnace to rule out the thermostat as my problem. I have red, green, white, and blue wire. My understanding is white – heating, green – fan, red – line off the low VAC transformer. The yellow from thermostat goes to the condenser, and the other condenser line to blue at the furnace (furn ground). It seems to me like touching the red and green together would cause the fan to kick on. Is this not right?
thank you,
remodeler
Replies
You are correct, if you jumper the red and green together the fan should come on. The tstat is really just a fancy switch, one that switches the power from the R terminal to G for fan, or W for heat. For cooling however it is necessary to jumper from the R terminal to the wire, not connected to the neutral on the furnace, going to the condensing unit outside. This will energize the contactor on the outdoor unit which, if the power is on, makes tha compressor and condensor fan motor run. To make the indoor fan come on, either jumper the R to G or turn the fan switch on the tstat to run. Hope this makes sense.
Thanks Fred. I think my problem must be a safety trip in the furnace. I have line voltage and low VAC in the furnace, and bypassing the t-stat doesn't trip the fan.
remodeler