My A-coil was leaking this summer, and my air conditioning went out. I decided to wait to replace it until next cooling season thinking that my furnace would still function. I turned on my heat this October and it was working fine... for a while. It stopped heating (still blows air) just before Halloween. Does this mean that my A-coil has something to do with how my heater works as well as my air-conditioner?

If I replace my A-coil, will this solve all my problems. I do have a very old Honeywell thermastat. Could this be my problem? Everything (Rheem AC & furnace) are about 25 years old.

Is you outside unit a heap pump? If not the A coil has nothing to do with the furnace.