Goodman furnace/AC help
#1
07-09-18, 12:31 PM
Goodman furnace/AC help
Hi, I am hoping to get some help. I have a Goodman Model GMT0703 furnace with central AC. The air conditioning stopped working. Had a repair guy come and said it was the breaker, so he replaced it and it worked for 3 days then stopped again. Had another repair guy come and say it was the blower motor. I replaced it yet it still doesn't work. Neither the condensing unit nor the furnace fan comes on when I switch on the AC from the thermostat. So I was thinking it's either the control board or the thermostat that is bad, but I wanted to get some advice from those of you who know more about this than I do before I proceed. Could it be something other than the two things I mentioned? The control board light turns on when I push the furnace door switch in, and I hear a click, which I assume is the relay, but then nothing happens. Would the control board cause both the outside condenser unit and the inside fan to stop working? Or could it be something else? Any help would be greatly appreciated.
#2
07-09-18, 12:59 PM
Member
Since both the indoor and outdoor units aren't working, the first thing to check for is if you have the 24VAC control voltage. If you have a multimeter, with the thermostat turned OFF, measure the voltage between the thermostat R & Y terminals. You should measure 24VAC. If you measure 0V, check to see if you have a fuse on your furnace control board (typically a 3A automotive fuse). The 24VAC comes from a small transformer in or near the furnace. If the fuse is good, or there is no fuse, check to see if the transformer is working (120VAC in, 24VAC out).
#3
07-09-18, 06:20 PM
Group Moderator
Welcome to the forums.
The red light on the main board is usually a good indicator of the 24vac is present as that board runs on 24vac. It should turn on solid and not be flashing.
That uses a basic board. It has W, G and R on it. The metal chassis is the C connection. You need to check for 24vac from R to the metal frame. A short directly from R to G should make the blower come on. The yellow from the the thermostat doesn't connect to the board.
Service manual... gray cooling man/uploads/1/0/6/6/10667336/g.pdf
The red light on the main board is usually a good indicator of the 24vac is present as that board runs on 24vac. It should turn on solid and not be flashing.
That uses a basic board. It has W, G and R on it. The metal chassis is the C connection. You need to check for 24vac from R to the metal frame. A short directly from R to G should make the blower come on. The yellow from the the thermostat doesn't connect to the board.
Service manual... gray cooling man/uploads/1/0/6/6/10667336/g.pdf
#4
07-11-18, 06:32 AM
Thanks for the replies, very helpful. The fuse on the board looks good, it isn't blown. The red light on the control board stays on. Would that light still turn on if the transformer is not working? Switching the thermostat to on, off, or fan does nothing. Is there anything else that could be causing this other than a bad board/thermostat/transformer? I will try the R to G short when I get a chance. Thanks again!
#5
07-11-18, 07:01 AM
Member
Pete said that the board is run from the 24VAC, so if the red light is on, then the transformer is good. To rule out the thermostat, connect the R terminal to the G terminal on the thermostat. If the blower comes on, then the thermostat is bad.
#7
07-19-18, 06:17 PM
Group Moderator
Very interesting. If the new board fixed the problem then the likeliest cause of the problem was a loose/defective connection. Possibly in the 9 pin connector. The board supplies the 24vac to run the A/C but does not run the condenser.
