newer furnace electrical problem

**pool_shark_dc** · 08-25-2011, 09:34 PM

got rid of older furnace for a little newer one. must have bumped something cause i got a wire that's not hooked up. i got an M1MC 077A BW. i will add attachment for wiring but i got gray wire that according to the diagram is supposed to go to 24v to the tstat. this diagram shows 4 stat wires of gray, red, green and white. my stat has yellow, red, green, white and blue(not used). am i supposed to hook up the gray to the yellow ?? prolly shouldnt have but i had the power to the furnace on and i connected that gray wire to the yellow wire from my stat and the furnace blower just kicked on and didnt go off. am i missing something? the gray wire in question is the wire in the middle of diagram that goes through the top

**jimbo** · 08-26-2011, 06:44 AM

Your diagram is too small to read. But my general comment is that you can't hook up HVAC by colors.....there are some conventions observed but too many loopholes. You need to take your furnace diagram, and the install manual for your thermostat...and find out what wire on the furnace need to go to what wire on the stat.

**pool_shark_dc** · 08-26-2011, 09:09 AM

might this help. i have a lux 500 tstat. there are 2 extra wires on there that go to another tstat. i am only wondering if you can help with the ones that go to the furnace

**jimbo** · 08-26-2011, 07:23 PM

The gray from your furnace is COMMON. Your thermostat does not have a COMMON connection. You will use the RED to rc/rh, GREEN to G, WHITE to W That.s it. If you have an air conditioner, the YELLOW tstat wire goes to the outside unit.

**pool_shark_dc** · 08-27-2011, 04:10 AM

what about the white one from the a/c unit ?? i am assuming the red wire from the a/c goes to the yellow but what about the other ? i'll hook it all up like you say and report back. got to put the bottom end covers together too.
so just tape off the gray wire then ?
another question i have is will the furnace heat work correctly if the bottom end is all opened up? i know there is a pressure switch but didnt know if that made any difference whether the bottom was wide open or not ?