Long story short: with both units on one breaker, each one is kicking on one after the other to try to reach one temperature. I have turned the a/c disconnect at the outside box, and the a/c is still kicking on. Replaced the thermostat and it is set on heat and auto fan, just in case it was defective, and that still didn't help. What is another way I can shut the a/c down since I can't flip the breaker off either, or then I would lose the furnace too.

  • 1
    You're going to have to tell us the make and model of all the equipment.
    – Tester101
    Nov 30 '17 at 2:04
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    Also is this a new problem? Did you change thermostats or any equipment this year?
    – Tyson
    Nov 30 '17 at 2:12
  • Moved in in march, had been vacant, found a/c was kicking on even tho thermostat was turned off. Didn't need a/c or heat at the time, so we ended up turning a/c off at breaker. When we tried to use a/c, it was not cooling enough, so we turned it off again and used window units. We did not know c/a was on same breaker with furnace at first. So now we found that they are both working against each other and i can't find a way to just turn a/c off so the heat can run by itself. Nov 30 '17 at 2:56

This is a broken thermostat, miswired furnace, or normal operation that you are mistaking for something else.

The fact that they're both on the same circuit breaker has nothing to do with it.

Shutoff switches positively deny power to the A/C condenser unit. It is impossible for the A/C to function with the switch pulled. On the other hand, how would you know? What you hear inside is the interior fan, which may run in conditions other than A/C.

Most typical forced air furnaces in the US use the same fan for both heat and A/C.

It should be literally impossible for the thermostat to command heat and command A/C a short time later by itself. Most 'stats require you to throw a switch to run A/C or heat... even smart stats like the Nest are modal and require you to switch it manually or on a timer.

  • I have literally sit at the vents and can feel cold air running for about 15 mins, then it will shut off and approx. 3 mins. later the heat will kick on and be warm in less than a min. So even tho I understand your reasoning that it should be impossible for both, it is most definitely what is going on. We replaced the thermostat, and during the summer when the a/c wasn't cool enough, we would have the thermostat set to the "off" position and the a/c would still kick on like it would set to "cool". We ended up having to turn it off at the breaker, so if either is faulty, should be a/c Nov 30 '17 at 13:27
  • Anyway, I am not so much concerned at this point about diagnosing it as I am to just being able to shut the a/c off so the heat will run by itself. Outside box set at "off" to disconnect, and the a/c is still running. It can buy me some time to have whatever it is serviced. Nov 30 '17 at 13:33

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