heil t-stat issue

toymech

Hey great site. I have a heil ultimate III furnace in my house I bought 8 Months ago. When i moved in I put in a Noma digital 5+2 tstat, works great. Last week got a noma digital 7 day tstat, hooked it up and the furnace just cycles the draft motor on and off in about 15 sec intervals. I took it back got a new one, same thing. The old one still works fine. I am an automotive tech so I started trying to figure out what was happening. An ohm meter shows both tstat's the same. accidently (sort of) I grabbed the two wires (one in each hand) and the furnace did the cycle thing. The 7 day works fine when calling for heat, but acts up when off. Any ideas? Thanks in advance

hvaclover

Bleeding voltage back.

Need an isolating relay.

__________________
Just slow, not stupid.

toymech

Hey Thanks. Got thinking about what you said and remember seeing an automoyive relay with a capacitor or resistor in it to stop arcing of the contacts. So I took the stat apart and sure enough there was a cap and resistor linking the two contacts together, so I cut the resistor. Works great now Thanks again