I have a gmnt 80-4b furnace that stopped running. The vent motor is not getting any power. I have power at both sides of the high limit switch, power to the flame sensor, and power to one side of the pressure switch. Anybody know why I am not getting power to the vent motor?

Make sure you have 24v on the W circuit. You may have a bad thermostat or broke thermostat wire. Jump from R to W to see it it will start working.

The thermostat is working and calling for heat. I have power at the W terminal, but the venter doesn't respond to the call. I have replaced the control board wire for wire, and have also replaced the pressure switch and still no luck.

If you have an open vent limit switch or rollout limit switch it will keep the inducer motor from running. The two are manual reset limits(small button in the center of the limit switch)Locations: rollout limit just above the burners, vent limit on the vent pipe just above the inducer motor inside the furnace.

The rollout switches are not tripped and I see no sensor on the vent pipe. I am not sure if a draft inducer is the same as a venter or if there is a difference based upon the furnace efficiency, but my furnace is vented with pvc pipe and there are no sensors on the vent pipe. The limit switch I found on my furnace does not have a reset, but I jumped it out and it made no difference.

You should have a diagnostic light telling you what's wrong.

3 blinks--either bad pressure switch, blocked vent, or bad venter. I have checked all these possibilities already. I have manually opened and closed the pressure switch with no results, and checked for blockages. The problem is the venter doesn't even try to start because it gets no power.

Check the switch on the venter motor itself if it has one. There should be power wires going to the vent motor and switch wires if your goodman is so equipped.

Also did you check the pressure switch contacts for continuity (open and close) with a meter if so equipped when you manually tested it?

If you do not have 120v going to the inducer motor(venter motor) after you reset the control board by turning the power off for a few seconds and then back on with your thermostat calling for heat I would say you have a bad control board or bad inducer relay. Depends on if your motor wires go to the control board or relay.

The motor wires go to the control board and I have already changed the board out with no luck. Do you know anything about the integrated fan/ignition control that the manual says is located in the air blower compartment? It says it is not field serviceable and I am wondering if this may be my problem.

I also have a Janitrol/Goodman furnace model GMP100-4 with similar problems. After trouble shooting the pressure switch and cleaning everything out (there was no blockage by the way) I'm finding that my issue is the venter motor itself. It gets power after power-off reset and closing door switch, but the motor does not respond. I get a high pitch humming from the control board area as well. I'm trying to locate a new venter motor now. It looks like I have to buy the whole venter assembly as a replacement, housing and all. It sounds like you don't have power to the motor in your case, but did you try turning off the power for a minute or two to let everything reset and then test for power to the motor?

If you will supply a accurate model number I will try to locate your furnace and take a look.

I have finally figured out the problem. The second control board I installed was also bad. I tried a third board and it fired right up. Thanks to everybody for your input.