- Make certain that the thermostat is set higher than the actual room temperature and the selector switch is on heat if heat is needed, or that the thermostat is set lower than the actual room temp and the switch is on cool if air conditioning is desired. If the thermostat is programmable, be certain the batteries are fresh.
- Test for power to the air handler by moving the fan switch from "auto" to "on". If the blower runs, the air handler is functional. If nothing happens, check the circuit breakers on the air handler cabinet and the breakers or fuses in the main panel. If any breakers are tripped, reset them once. If they trip again do not reset them. Deadly high voltage conditions exist inside the air handler cabinet and inside the access panel of the condenser. Let a qualified serviceman open them.
- If the air handler runs constantly but cannot satisfy the thermostat setting, it is possible the backup heat is running but the condenser is not. Some condensers have the high pressure cut-out switch externally accessible. Look for a button sticking out of the cabinet in the vicinity of the refrigerant pipes. Press it in. If the machine starts up, the head pressure got too high, possibly from turning on and off too quickly, too much or too little refrigerant, or an electrical interruption. As the unit ages , the switch can weaken and pop easily. If the condition repeats itself often, have a serviceman check it.
- Because all the controls are internally mounted, and high voltage wiring is exposed, only a serviceman should open panels.