[tnr580]

Initially stopped heating after 5-6 mins with coils chattering, set idle for 30 min and then repeatable problem. Did a thorough cleaning, no help.

Replaced gas coils and that corrected the 'no heat aft 5-6 min' problem.
Now notice the timer does not move in auto high-heat and auto low-heat modes. Timer does advance fine in timed and air modes. Replaced the timer,... no help.

Now suspected the operating thermostat, but it operates as follows:
- in high heat it opens at 169, closes at 130.
- in low heat it opens at 159, closes at 120,.. per the meat thermometer in fuse hole slot and checking with a voltmeter on the side that drops from 115v to 25v.
Not what I expected if the operating thermo was bad.

Need direction on fixing the auto timer issue. Not much left to replace,.. what makes the timer advance in the auto dry mode?

[bettyboop]

You are looking at the operating stat for the wrong reason. I believe the operating is the culpret, the contacts with the little wires on it, control timer movement, when stat cycles, timer is allowed to move a little, replace it and the hi-limit also, it's old too.

[tnr580]

Thanks, I'll replace the operating thermostat and will advise.

I was thinking the smaller connections were the bias heater connections for operation in a low heat mode.