Old Lenox GH6D-80C

Jwooten08

I have a heat only system in a small apartment. It's wired up for constant fan on a 2 wire mercury thermostat, is there a way to run a 3 wire to an updated thermostat where the blower auto shuts off.

Picture's are attached.

mattmia2

you'd have to add a relay to have a "fan on" from a thermostat. I can't see the fan/limit control well enough to see if the off pin is missing from the control or turned all the way down or is too close to the on pin but if the fan control is working correctly the blower should shut off when the furnace cools.

109A_5

Hello Jwooten08,

Looks like you are in Manual mode. Hopefully the AUTO mode works correctly. Where is the cover, live wires in there and the cover labeling is missing?

retiredguy

Try moving the lever that @109A 5 indicates with the red arrow up to a setting above 100 degrees. Push the tab in slightly, hold the dial so it doesn't turn and move the indicator. That should allow the fan to cycle off unless that fan/limit control is bad. BTW, that model furnace had heat exchanger problems where the steel heatX would crack making it dangerous to your health. That GH-6 unit is probably from the 1970's and should be carefully checked by an experienced tech.

worldclasshvac

The lever 109A pointed to is the manual/auto mode lever for that control. Sliding it up should put it in auto and let you use fan control off the limit. Then you can adjust temp to come on correctly

mattmia2

That looks more like it is from the 50's, but the HX still needs to be checked.