A heat pump is an appliance that extracts heat from one environment and discharges it into another. Most heat pumps are powered by an electric motor, but can be powered by a fuel burning motor, as some camper refrigerators are. In heating mode, a heat pump will collect heat from the outdoor unit (condenser), and discharge it inside through the air handler. With the help of a reversing valve, the flow of refrigerant moves in the opposite direction and heat is extracted from the air handler and discharged outside, creating air conditioning.
In some tropical areas, domestic hot water is generated in air conditioning mode by cooling the condenser with water, the heated water is stored until needed.
It’s basic components are: the air handler; comprised of a cabinet, blower, evaporator coil, and controls, The condenser or outdoor unit, and piping to create a closed loop of refrigerant between the two.
In some areas the heating demand can be two or three times the cooling demand. Because a heat pump’s efficiency drops as the outside temperature goes down, electric heating elements will be installed as a backup to assist the heat pump when needed. Accessories include: an air filter, electronic air cleaner, or high performance media filter, and a humidifier. A condensate pump might be used to remove the water produced be the dehumidifying action of the air conditioning.
A zone control panel and motor actuated dampers will be attached to the unit or in the ductwork if the system is zoned. Routine maintenance includes replacing the air filter or cleaning the electronic grids, and cleaning the humidifier. Heat pump humidifiers can be of the steam generating type, which will be line voltage powered, so caution must be taken to shut off the power supply before servicing.
Basic troubleshooting: 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.