Intermittent no heat / fan constant problem...

[GregCathey]

Hi guys, I have a weird problem with my gas furnace and found this site while searching for a good HVAC troubleshooting site. I did a little bit of this work on a submarine in the Navy - but that was thirty years ago.

This has been an intermittent problem the last few weeks but its getting more frequent. The heat will operate normally for a few cycles, then at the end of a heat cycle the fan will not shut off, even with the thermostat turned off completely. After a while (an hour or more) the fan will shut off by itself. Same thing over and over. When it's in a properly working cycle the themostat controls work fine - you can turn the unit on, off, auto, etc. but when it's in a bad cycle the t/stat has no effect on the unit.


I assumed it was some type of overheat protection circuit. so far i have tried a new thermostat, bypassing the rollout limit switch, and the flow switch. I noticed when its in the "no heat" cycle the draft inducing fan runs constantly.

I'm thinking I have a bad board but thought I'd ask around.


The unit is a Tempstar / ICP Model # is PGME36G080E ...

Any input is greatly appreciated.

[Freon]

Try re posting the Tempstar model number. Only use letters and numbers, no symbols.

Go to the furnace and find the control board. Look for the C, W and G terminals.

When the blower does not shut off after a heating cycle, make sure you wait about 2 minutes after the burners shut down. Then measure the AC voltage between W and C then between G and C. There should be 0 volts AC if there is no call for heat or the blower (fan). Carefully examine the control board for cold solder joints. Intermittent means something is loose or slowly deteriorating.

Let us know what you find.

[GregCathey]

Freon -
> Try re posting the Tempstar model number. Only use letters and numbers, no
> symbols.
>
> Let us know what you find.

Thanks for the quick reply - I'll try it out next failed cycle. Below is a pic of the specification there sticker, there is a Tempstar emblem on the front of the unit but no model info. I think ICP makes Heil, Tempstar, and maybe other units.

I assume the Tempstar model is either PGME or PGAD... The sticker says
INTERNATIONAL COMFORT PRODUCTS ICP
MODEL. PGME36G080E
MFR. PGAD36D1KE


EDIT I tried to post a pic of the label but no luck...

[Freon]

Those model numbers take me to Heil AC condensers. Keep looking around the furnace usually on the back of the main blower cover.