Have a goodman GMP075-3 that won't turn on when thermostat is set to Auto. I will only turn on when set to the "ON" but will blow cold air. Status light blinks 3 times. Code notes suggest to" "check Venter Pressure Switch Vent Blockage" I think it is the pressure switch since I do not have a vent blockage. Should I replace the Pressure Switch? Your Advice?
With a meter you can can test continuity. This will tell you if the switch has failed. Always be safe and turn power off, when testing continuity through switches unhook at least one side of the wires. Best wishes.
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Hello,
The t-state set to fan "ON" will only cycle the fan to turn on only nothing else. "Auto" is where you always want the t-state on when you want to have heat and have the fan cycle off automatically after the t-stat has reached set point.
As for the press switch, there can be two things that will cause the pressure switch not to close. 1: obviously the switch itself and 2: the inducer fan, this has the rubber tubing that connects to the pressure switch.
When you call for heat, the inducer fan ( small fan with black plastic piece that spins ) is the first to turn on, this fan makes sure any left over exhaust air/gases are vented out before the burners turn on, it also stays on the entire heat cycle to exhaust the gases. The pressure switch needs proof of air so the pressure switch closes with the vacuum that is being created by the inducer fan in that rubber hose that is connected to the pressure switch. This allows the furnace to know " my induce fan is working, lets proceed".
So,
I would make sure your inducer fan is working. if you don't see it working then I recommend using a multi-meter ( VAC setting) and checking that you have 120volts supplied to the inducer fan. if you don't, then you need to work backward from there and see why you don't. If you do verify 120volts at your inducer motor, then more than likely it failed and will need a new one. Witch out this, your pressure switch wont close.
If your inducer fan is working fine then make sure you have 24vdc across you pressure switch (again with a multi meter but with VDC setting not VAC). 24vdc in and 24vdc out. If you only have 24VDC in but not out, then you pressure switch may be stuck open. ( This is if your inducer fan is working properly).
I hope this helps. Sorry for the long response. I just don't like people changing parts and wasting money.
SOURCE: goodman furnace wont come on
If this is a High Eff furnace:
1) Remove the compartment that has the igniter and burners, turn the
power back on, if the furnace lites then you have a problem with the
intake air vent, probably iced over if you live where its cold.
2)Make sure the exhaust vent is not getting backpressure from the
wind.
3) you could cut the pipes on the inside of the house to disconnect them from the furnace, test run the furnace with no pipes.If the furnace
runs then you have a problem with the installation of the vent pipes.
4) Do not run the furnace without the exhaust pipe disconnected,
go to the hardware store and get a couple of rubber clamped
couplings and hook-up the exhaust pipe!
Good Luck
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