If you're running your air conditioner to keep your house cool, but you keep hearing the furnace kick on, you might have a problem with the AC and furnace running at the same time. This is often caused by a wiring problem, so you'll need to call an air conditioning repair service to figure out what's wrong so your house can cool down properly. Here are some things the air conditioning repair technician might check.
The problem might be that the thermostat is sending a signal to the furnace and air conditioner at the same time so they both kick on even if the thermostat is in the cooling position. The technician can verify if that's the problem by manually turning on the AC and furnace one at a time.
This problem might happen when you get a new thermostat and it wasn't wired properly. In that case, the technician can fix the wiring and solve the problem. It's also possible that the thermostat is bad, and in that case, the repair technician can replace it.
The Control Board
The wiring from your thermostat goes to the control board that's located in the air handler part of your AC. If any of the wires are loose or defective, the control board might not be able to control your air conditioner properly. The air conditioning technician can remove the wiring coming from the thermostat to verify if the problem with your AC is in the thermostat or the control board. If your furnace and AC kick on when the thermostat wires are disconnected from the control board, then the problem is probably a bad board.
When the control board is bad, the air conditioning repair technician can replace it by locating the exact control board needed and putting it in the air handler after the bad board is removed. The control board has many wires connected to it, including wiring that goes to the condenser outside, so it's important to put all the wiring back in place properly on the new board so your AC functions properly.
Bad wiring can cause your air conditioner and furnace to run at the same time. If wires touch because they are too close at the connections or because they are touching in the insulated sleeve, your AC malfunctions. The solution for this is to rule out malfunctions with the control board and thermostat and then replace the wiring to see if that fixes the problem.