[ssyba]

Hello,
I am having issues with our gas furnace starting.
When the thermostat clicks on the fan will turn on for 1-2 seconds then flip off. If I keep resetting the system then I can get it to turn on randomly after several tries of turning it off and on.
Does this seem to be a start capacitor problem? Any other ideas?

Thanks!

[ssyba]

An update after investigating a bit further: The furnace is a Goodman GMP100-5. And the problem has to do with the exhaust fan not the main blower for the central system. So when the furnace tries to start up, the exhaust fan goes on for 1-2 seconds then will sometimes shut down. When this happens the only way to get it going is to constantly reset the system by turning the master switch on and off until the exhaust fan successfully fully starts. There doesn't appear to be a capacitor conntected to the fan. The power for the fan goes directly to the circuitboard. Any ideas?

[hvac_hillbilly]

you probaly should have this checked sounds like one of the limit switches locking out the furances and you are reseting the board every time you mess with thermostat please be sure your furanance is not overheating this is dangerous

[hvac_hillbilly]

this sounds like the pressure switch to me let me see if i can find a link for you

[hvac_hillbilly]

allpartsheating.com

[John @ Fischers]

When the vent motor shuts off, check and see if you still have 120V supplying the motor. If so, then the motor is bad. If not, then there is a reason the power is being interrupted to the vent motor.

This could be a bad control board, short in the wiring system, an open limit, or a bad limit that is opening intermediately, a bad thermostat. Or, last but not least, a true problem that is causing the limit(s) to open.

The PSI switch is only closed after the venter motor is running long enough to create a negative vacuum, which in turns "closes" the PSI switch which then will start heat cycle if the limits are closed. If the vent is blocked, then the switch will never create a vacuum. Thus is a good thing. But i would say in your case, vent blockage is not an issue, even though don't take it for granted.

Does the circuit board have a green lite on it? if so, most time after system failure, it will flash 1-8 times repeating the same amount of flashes, informing of what failed.

See if it has so, post back.

[goodfella08]

could be a bad pressure switch (attached to that motor via small hose) or clogged exhaust. Maybe birds nest at the end of it.....??

[tvtech]

Most those new furnaces have a blinking light to lead you to the problem.
But basically.. 1. exaust fan turns on
2. vacuum swich must be activated to continue
3. ignitor turns red maybe 15-30 seconds
4. gas valve turns on
5. flame sensor must detect heat to contiue
6. after a minute or so large fan turns on
7. until thermostat satisfied
8. there are several over heat sensors if one of those trips out usually the furnace will just run the large fan only and no gas..
Sounds like your not making it to the ignitor red stage so check out the vacuume switch.. also a blocked flew will cause same problem.
Thats the best i know..