[wfigura412]

The Model #398AAZ048100AAKA furnace does not have a dummy light that gives codes. Here is what happens:

Thermostat calls for heat. Draft inducer motor starts. Pressure switch closes. Draft inducer runs for anywhere from a couple seconds to the pilot lighting then there is a click in the gas valve. Once that happens the inducer motor runs for ten seconds and the furnace shuts down and goes into a lock out until I turn the power switch back off and on again.

If the burners light then it will runs it's cycle until the thermostat is satisfied. The pressure switch works, the limit switch is fine, the pilot and flame sensor are OK. I replaced the inducer control board last winter.

So I think the problem is in the main control board, the ignition lockout, or the gas valve.

Any help would be appreciated.

[T-Top]

This is one of the harder ones to trouble shoot even for a service tech. To begin with the old five wire gas valve has a pick and hold circuit that can go bad(not a cheap part)The system uses a three wire pilot assembly that is known to stick(not a cheap part) and it uses a inducer control board that hooks into the main control board(cheaper than the first two but not cheap) Any and all of the 3 parts when going bad give your symptom. It may be time to call for service. This is the type system that a service tech. Hates to see. Easy thing to check is to make sure you have a good strong pilot flame.

[wfigura412]

Most times it never makes it to the pilot lighting. But you may be on to something with the pick and hold I have been trying to research it. Before it shuts down something pops in the valve and 15 seconds later the inducer stops. I replaced the inducer control board last year (when it locked out much less) but that didn't work I'm leaning toward the gas valve but need more info on pick and hold circuits before I'm convinced

[T-Top]

A bad 3 wire pilot assembly will get it bouncing back and forth. It's a bimetallic strip that has to make or break no in between or it shuts down. A bad pilot assembly will keep the inducer motor from running.

[wfigura412]

So I checked the pilot assembly and I don't have a problem there yellow is common green is normally closed and works fine and white is normally open, and it closes if the pilot lights then the burners come on. The noise I thought was coming from the gas valve I actually think its flocking from the ignition lockout control. So any educated guesses as to the problem is it the main circuit board or the ignition lockout