Goodman GMP-050-3 won't start
#1
04-03-21, 12:04 AM
Goodman GMP-050-3 won't start
I'm having a weird issue with my gas furnace and I can't seem to figure out what's going on from the service manual. The best I can figure is that it's a bad board.
A few days ago, my Nest thermostat disconnected from Wifi and after I reset it, I couldn't get any heat. When I turn on the heat, nothing happens. No inducer motor, no blower, no gas, no ignition. It's like birds chirping. However, the blower and AC work fine when those are individually selected.
I tried jumpering W1 to R on my board and it's the same thing, so it doesn't appear to be the thermostat. The status light on the board is solid red indicating normal operation. I checked the pressure circuit and it's open (24V differential measured across it, and infinite resistance), which is what it's supposed to be according to the startup sequence.
I thought it might be a bad inducer motor, but the motor spins freely and it measures continuous with my multimeter.
I also tried hooking up my multimeter to the power terminals for the inducer motor on the board. When I call for heat using the jumpered connection, I get 1V across the terminals when they are disconnected from the motor. I also tried hooking up the multimeter in sequence with the inducer motor and got 0 amps when calling for heat.
All rollouts have continuity and the control limit switch shows continuity as well.
I measured the voltage across the Rh and W1 pins and it shows 28VAC, which is within the range I expect.
Anyone have any ideas what this might be? The only thing that makes any sense to me is that it's a bad control board. My guess is that the board failed and that's what caused the thermostat to misbehave. Resetting the thermostat fixed it, but the board is still shot. Is there anything else that might cause a no heat condition without triggering a blinking status light?
A few days ago, my Nest thermostat disconnected from Wifi and after I reset it, I couldn't get any heat. When I turn on the heat, nothing happens. No inducer motor, no blower, no gas, no ignition. It's like birds chirping. However, the blower and AC work fine when those are individually selected.
I tried jumpering W1 to R on my board and it's the same thing, so it doesn't appear to be the thermostat. The status light on the board is solid red indicating normal operation. I checked the pressure circuit and it's open (24V differential measured across it, and infinite resistance), which is what it's supposed to be according to the startup sequence.
I thought it might be a bad inducer motor, but the motor spins freely and it measures continuous with my multimeter.
I also tried hooking up my multimeter to the power terminals for the inducer motor on the board. When I call for heat using the jumpered connection, I get 1V across the terminals when they are disconnected from the motor. I also tried hooking up the multimeter in sequence with the inducer motor and got 0 amps when calling for heat.
All rollouts have continuity and the control limit switch shows continuity as well.
I measured the voltage across the Rh and W1 pins and it shows 28VAC, which is within the range I expect.
Anyone have any ideas what this might be? The only thing that makes any sense to me is that it's a bad control board. My guess is that the board failed and that's what caused the thermostat to misbehave. Resetting the thermostat fixed it, but the board is still shot. Is there anything else that might cause a no heat condition without triggering a blinking status light?
#2
04-03-21, 04:08 AM
Group Moderator
I rather frequently find control boards with cracked solder joints, usually at the header pins where you plug in the cables.
#3
04-03-21, 12:36 PM
Thanks for the response. I did take the board off of the mount and inspect it for burn marks and cracks. I couldn't see any, but I also didn't disconnect the board, either.
#4
04-03-21, 01:40 PM
Group Moderator
When you connect W to R you should hear the draft inducer relay click and then the inducer should start.
#5
04-03-21, 04:07 PM
Member
The Nest devices have been known to cause damage to equipment electronics. One of the many issues they cause.
Were you using a common or using it as a power stealing seat up?
Were you using a common or using it as a power stealing seat up?
#6
04-03-21, 11:04 PM
@PJmax: Connecting W to R does nothing. The inducer does not click nor start. There's 28VAC between W and R, but nothing happens when I do that.
@roughneck77: It's using a common wire.
@roughneck77: It's using a common wire.
#8
04-04-21, 09:21 AM
Group Moderator
There's 28VAC between W and R,
The board should acknowledge a W connection.
The relay should click with a W connection.
It's either an open limit or a defective board.
I'm leaning towards defective board because the fault light would show an open limit circuit.
jason1983
voted this post useful.
#9
04-04-21, 10:58 AM
@Geochurchi - The first thing I did was I pulled the thermostat off the wall and connected them there. When that didn't work, I pulled the wire nuts off the two wires in the furnace box and held them together with a pair of pliers. When that didn't work, I pulled the connectors off the board and wired them together directly with copper wire.
@PJmax - If it's an open limit, I don't see what it could be. I tested all the rollout switches and limit switches with my multimeter and they all showed continuity.
@PJmax - If it's an open limit, I don't see what it could be. I tested all the rollout switches and limit switches with my multimeter and they all showed continuity.
#10
04-04-21, 08:39 PM
New and interesting developments.
I wanted to test the inducer motor, so I hard wired it to the primary side of the transformer. After doing that, the motor starts normally and then the furnace fully starts. However, I have a new problem now. You can see it in this video. At first, the flame looks OK (although I'm not sure the flame is supposed to be hitting the igniter like that), but then around the 18 second mark, the blower comes on and the flame starts dancing a lot more. I think this probably indicates a cracked heat exchanger.
I wanted to test the inducer motor, so I hard wired it to the primary side of the transformer. After doing that, the motor starts normally and then the furnace fully starts. However, I have a new problem now. You can see it in this video. At first, the flame looks OK (although I'm not sure the flame is supposed to be hitting the igniter like that), but then around the 18 second mark, the blower comes on and the flame starts dancing a lot more. I think this probably indicates a cracked heat exchanger.
#11
04-04-21, 09:04 PM
Group Moderator
I would concur. That looks to be a cracked heat exchanger.
The blower should not be causing the flame to leave the burning chamber.
The blower should not be causing the flame to leave the burning chamber.
jason1983
voted this post useful.
#12
04-05-21, 09:38 AM
I had ordered a new board to replace the bad one, but now that I know I also have a broken heat exchanger in addition to a bad board, I think I will replace the entire furnace and return the new board.
#13
04-13-21, 03:56 PM
Member
Your furnace is unsafe to run, it pretty much has to be replaced.
that furnace even without the bad heat exchanger is not worth spending a cent on.
that furnace even without the bad heat exchanger is not worth spending a cent on.
#14
04-14-21, 03:43 PM
@user10 - I haven't turned it on since I discovered the bad heat exchanger, and I have arranged to get an estimate on a new Carrier furnace. Things are pretty backed up around here, but I should have an estimate next week. In the mean time, it's staying off. I don't really want to die from CO poisoning.
If it had just been the bad board, I would have replaced it myself. For $150, I think that would have been worth it to get however long that furnace has left. But the furnace is from 1994, and you're right that it's probably about time for a replacement anyway.
If it had just been the bad board, I would have replaced it myself. For $150, I think that would have been worth it to get however long that furnace has left. But the furnace is from 1994, and you're right that it's probably about time for a replacement anyway.
