gas furnace wont let gas vave open

hutch07

I'm trying to fix a gas furnace ans when it comes on it does not run the normal sequence. The induce draft motor and blowr motor come on at the same time. The pressure switch pulls in but the gas valve won't open. I can pull the tube off and manually get the vale to open by sucking on the tube then put the tube back on the IFM and it will engage the pressure switch and the gas valve will open but when I turn the unit off it won't open again on its own. This is a comfortmaker. Am I wromg in suspecting the gas valve and why is it not running in the normal order.

kenmac

try to clean out the small port where ps hose connects to vent motor. Sounds like it's clogged

beenthere

It isn't the gas valve. Or the valve wouldn't open when you suck on the hose and put it back on the inducer port.

hutch07

I already cleaned out the port. Once I suck on the hose and get the valve to open i can pull the tube off and on and the gas valve opens and closes. But if I turn off the heat then it wont come back on. And still dont run the proper sequence. Any Ideas?

kenmac

Connect a vm to the ps terminals on a call for heat. If the switch is staying open you will have 24v across the ps. if it closes you will read o with vm

beenthere

Might have a thinning inducer blower wheel.

If you suck on the hose. And then put it on, and everything works.

Shut the furnace off for 10 minutes, and then turn it back on. If it works again without sucking on the hose. You may be getting moisture in either the hose, or pressure switch.