The condenser for a heat pump and a central air conditioning system look similar and are
constructed of the same basic parts. A cabinet houses the components and is strong enough
to protect them during transport and installation. Inside of the cabinet will be a condenser
coil, a compressor, a fan, and controls.
The coil is usually made of copper tubing with aluminum fins, but some manufactures use
aluminum tubing. Its purpose is to transfer heat as rapidly as possible. Pressure inside
the coil can exceed 400 psi., during extremely warm weather conditions. The cleaner it is
kept, the better it transfers heat. Rinsing with a garden hose occasionally when the unit
is not running will help keep it operating efficiently. After many years of use it may be
necessary to put special chemicals on to clean it.
The condenser fan moves air across the coil to increase the transfer of heat. It is critical
to the system. Obstructing the flow of air will not only reduce efficiency but can lead
to compressor failure. Keep debris and objects away from the coil and fan to allow maximum
air flow. Some condenser fan motors have sealed bearings, others need lubrication. Damage
to the fan can occur if removed improperly. Have a qualified serviceman handle the lubricating
The compressor is the engine of the system. It compresses the refrigerant and pumps it
to a coil as a hot gas. For air conditioning, it will be cooled at the condenser into a
warm liquid and piped to the evaporator coil to expand and cool. For a heat pump, the hot
gas will be pumped directly to the evaporator coil to provide heat. Compressors are of two
designs; reciprocating and scroll. A reciprocating compressor is similar to an air compressor.
An electric motor spins a crankshaft with pistons and connecting rods. Valves open and close
to allow the flow of gas in the desired direction. Special lubricants are used.
Since the system is hermetically sealed, the lubricant is permanent and does not get changed.
Reciprocating compressors have been in use since the first refrigerators. Scroll compressors
use an electric motor to drive them, but the similarity ends here. Its uniqueness is difficult
to explain, but it is ingenious. Using two spiral mazes recessed into each other, one attached
to a motor drive an d the other allowed to slide freely, compression occurs with rapid movement.
After many years of testing and engineering improvements, the scroll compressor is available
from some manufacturers as a standard or option in the condenser. It is both efficient and
quiet, and improve with age.
If the condenser is used for air conditioning only, controls are minimal. A contactor
switches the power on and off. Capacitors are used to start and run the motors. Optional
controls are: a brown-out time delay, crankcase heater. Hard start kit, and low ambience
A brown-out time delay protects the compressor in two ways. If the voltage drops and the
motors draw too much current(amperes) it shuts the contactor off. If the control voltage
is interrupted momentarily, it shuts the contactor off. When the compressor is running,
high pressure exists at the exhaust port. If it is shut down and restarted before the pressure
equalizes with the intake port, the motor will not be able to overpower the pressure imbalance
and overheat. The time delay will stall the restart for three or four minutes; sufficient
time for the pressures to equalize.
The compressor is deigned to compress a gas, not a liquid. A crankcase heater is used
to preheat the oil and liquid refrigerant that might have settled in the compressor crankcase.
By boiling off any refrigerant, risk of valve damage is avoided.
If rapid restarts are required for the system, a hard start kit can be installed. It consists
of a potential relay and a capacitor. It gives the motor an added jolt or boost to help
it start under stress.
Mostly used in commercial applications, a low ambience control could be used on a residential
system if needed. It senses the liquid line pressure and cycles the condenser fan to keep
pressure high enough for the air conditioning to function in cold weather.
If the condenser is part of a heat pump system, the controls get more complex. In addition
to the controls already listed, there will be a reversing valve, defrost timer, and possibly
an adjustable temperature sensor.
The reversing valve directs the flow of compressed gas to the condenser coil for air conditioning
or to the evaporator coil for heating.
When extracting heat from outdoor air, the condenser coil gets very cold and frost will
begin to form on it. Too much frost build-up will restrict air flow and reduce effectiveness
of the coil. The defrost control switches to air conditioning mode without the condenser
fan running. The hot gas running through the coil melts the ice that formed, then shifts
back to heating mode.
Some older model heat pumps have an adjustable thermostat in the outdoor control panel.
It will limit the low temperature operation of the heat pump to prevent it from running
when it is too cold out to extract sufficient heat from the air.