I just installed a new thermostat last spring and everything was fine until I had to turn my furnace on for the first time. (My furnace is a Janitrol forced heat) When my furnace kicks on, I notice that my outside ac unit also kicks on. Does this sound right? Or could it be a wiring problem in my thermostat or something else?

You probably wired your stat incorrectly. Did you jumper the two reds, Rc and Rh? You do this if you have only one transformer. Did you have both a yellow and a white wire coming from the furnace? What model stat did you use?

If this is a digital electronic thermostat, you may have it set up for heat pump operation and not gas electric, you may have a switch to move over or tell it in the set up that you have a gas electric. Good luck, Mkie

You probably wired your stat incorrectly. Did you jumper the two reds, Rc and Rh? You do this if you have only one transformer. Did you have both a yellow and a white wire coming from the furnace? What model stat did you use?

Thanks for responding! I did jumper the 2 reds. I do have a yellow and white wire coming from the furnace. The model is a LAX. How should I rewire it?

Thanks for being so helpful. You have me on the right track. For now, I just pulled the fuse on the AC unit outside.

Put me on the right track

There is a very complete explanation of wiring up thermostats at https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313.html

Did you check Acetc's idea? I find that far more likely than being miss wired. I can't see how you could wire it so the A/C ran OK but you get both it and heat on heat.