Furnace -Sometimes works... sometimes doesn't

[Bob]

Hello and Thanks for reading.
I have a Amana Air COmmand 80 Gas Furnace (Model #GHI07A30).

Sometimes The furnace controller turns on the furnace and it runs properly and sometimes it does not get to the ignitor - hot stage.

Observations:
Combustion Fan is running.
Cold air is blowing via only the combustion fan.
Closer Inspection reveals the heater going through a cycle every two mintes:
Time = 0 sec Combustion Blower on
Time = 50 sec gas comes on
Time = 55 sec gas off
Time = 120 sec gas on
Time = 125 sec gas off...

So what is missing here is the ignitor getting hot portion of the cycle. So I shut off the heater pull out the Voltmeter and start the trouble shooting. During the cycle I am not getting any voltage going to my ignitor.

Next I tap the Fan Limit Control Switch (Set at Fan off 100, on 130, limit 200) and the next time through the cycle my ignitor gets voltage and the house is now getting warm.

I think that the limit switch has nothing to do with the ignitor circuit but the fan limit switch is mounted on the same piece of sheet metal as the Ignition module. This could be wrong ...

Before I start tearing apart the heater so that I can get the module out:
a) Is there anything else I should check first?
b) Are there user servicable elements in the module itself?

Thanks for your attention and thoughts.
Bob

[Hube]

The COMBINED FAN-LIMIT control has nothing to do with your problem. The fan on/off settings control only the fan operation in the heat mode. The HIGH LIMIT part of the Combination control will shut the burner off if it reaches the set temperature (apprx 185 ) The problem seems to be in the ignitor or thermo coupler. Unless you have the proper testing meter, and know-how, your best to call in a pro. Good luck, hube

[Bob]

Hube, Thanks for taking a peek at my problem. I do have the proper testing meter (my fluke 87 is in competent hands :-)

I suspected that the tapping on the fan limit was jst a decoy and that the problem really laid with the Ignition Module, thanks a lot for confirming that for me.
Any thoughts on next steps?

[Hube]

Check out the contacts for corrosion on the terminals,etc. Clean the contacts. Good luck, Hube

[scott B.]

Hi, Hube
My problem of gas furnace is the same ( I have same furnace Amana Model#GHI70A30).
I have to knok the ignition module (while box from where the ignition wire is coming out)when the thermostate turns on the furnace in ordert the ignitor to become 'red'.
Some time the furnace runs smoothly for few hours and some time I have to knok that white box? I checked in the connection coming from white box to igniotor. I also replaced the ignitor. Do you have any idea ?