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davehs · Apr 1, 2007, 10:05 PM

Goodman GMPO75-3 ser9911605881 . When warmed up runs OK . Cold the DI fan runs then HSI glows,gas valve opens and it lights with woof woof and goes out in 5 secs . Cycles again and it might start or go on third try. I polished the fire rod, set GV to 3.5 ins then changed GV. 24 volts at the GV .Shut off gas when running , it tries 3 times then red light blinks once.It just failed when warm and the circulating fan came on even though the gas was on for only 5 secs,it lit second try. I had a tech check it out and no solution.The furnace is a 1999 but new to me. Any ideas

hvac1000 · Apr 2, 2007, 04:25 PM

Does the power drop off to the gas valve when running?

davehs · Apr 2, 2007, 06:01 PM

Hi. Furnace was warm and the voltage was between 24.4 & 24.8 at the gas valve the start up was smooth and quiet (no woof woof) I will let it cool and check it later tonight TNX davehs

hvac1000 · Apr 2, 2007, 07:06 PM

Does the power drop off to the gas valve when running?

I would like to have a answer on this. Was the voltage being supplied to the gas valva when the burner stopped working? This is what should be checked.

davehs · Apr 2, 2007, 10:03 PM

Hi, my furnace usually fails when its coldat night after its been off. Since 5 pm it has lit first time and stayed on 4 times. I have a voltmeter connected and just have to be there when it fails , its so intermittent TNX davehs

davehs · Apr 4, 2007, 12:26 PM

Hi the 24volt went off at the gas valve and the flame quit. Then lit on second tryand ran fine. Ihad cooled the DI fan with an ice pack to simulate a cooled furnace. The fan spins freely with no noise, Could it be anything else?? TNX davehs

hvac1000 · Apr 4, 2007, 01:46 PM

Try cleaning the flame sensor with steel wool. Sometimes if the sensor is a bit dirty it will not signal the circuit board that a flame is present and that will cause the furnace to shut down and retry.

davehs · Apr 4, 2007, 11:05 PM

Hi, Ialready polished the flame rod . I put a tach on the fan and its 3400 rpm? Should it not be 3000rpm or does that metter . davehs

hvac1000 · Apr 5, 2007, 01:58 AM

Next step is to follow the control wires from the Gas valve back. If this has a power combustion blower there is usually a switch attached to it or a pressure switch of some type to prove its operation. Chech for the proper operation of that switch.