T-stat mod. Why does a/c fan run when furnace is on

I saw this question in a previous closed post. None of the answers solved the problem for me. What did work was to flip the switch (inside the t-stat) from "gas/oil furnace" to "electric furnace" - and then switch it back. Also need to set the heat anticipator to 3 (as the previous post suggests)

When I did this, I tried the t-stat in " electric furnace" mode...then switched back to "gas" mode - and the a/c fan quit coming on in heat mode. I mention this because it may not be enough to just flip the switch and flip it back - and it may be all it takes. If not you may try

- flip the switch to electric furnace mode, try to run furnace, then switch back.
- or; flip the switch to electric mode, wait 5 minutes, and switch back to gas mode
- or; flip to electric mode, remove and replace batteries, and switch back to gas mode

I'm not an electrician. So I don't know what exactly what is happening, or why. I just know I was having this problem and fiddling with these switches, after double-checking that my wiring was right, solved it

Hope this helps. Saved me from scraping my $25 digital Hunter t- stat and having to buy the Domitan replacement for over $100 --- good luck

Moved to Tech Issues forum from DIY.