Refrigerant Charge Check—Units with Fixed
After completing the airflow measurements and adjustments, the
unit's refrigerant charge must be checked. The unit comes
factory-charged, but this charge is based on 325 CFM per ton
and a minimum ESP per ARI test conditions (generally between
0.15 to 0.25 ESP). When air quantity or ESP is different than
above, the refrigerant charge must be adjusted to the proper
Disconnect ALL power before servicing.
Multiple power sources may be present.
Failure to do so may cause property damage,
personal injury or death.
The self-contained package air conditioner or heat pump should
operate for many years without excessive service calls if the unit
is installed properly. However, it is recommended that the
homeowner inspect the unit before a seasonal start-up. The coils
should be free of debris, so adequate airflow is achieved. The
return and supply registers should be free of any obstructions.
The filters should be cleaned or replaced.
These few steps will help to keep the product up time to a
maximum. The System Troubleshooting chart should help in
identifying problems if the unit does not operate properly.
NOTE: The following information is for use by qualified service
agency only. Others should not attempt to service this
Common Causes of Unsatisfactory Operation of Heat
Pump on the Heating Cycle.
Inadequate Air Volume Through Indoor Coil
When a heat pump is in the heating cycle, the indoor coil is
functioning as a condenser. The return air filter must always
be clean, and sufficient air volume must pass through the
indoor coil to prevent excessive discharge pressure, and high
All package units with fixed orifice devices are charged using the
superheat method at the compressor suction line.
For charging in the warmer months, 8ºF ± 3ºF superheat at the
compressor is required at conditions 95ºF (35ºC) outdoor
ambient (dry bulb) temperature, 80ºF (27ºC) dry bulb/67ºF (19ºC)
wet bulb indoor ambient, approximately 50% humidity. This
superheat varies when conditions vary from the conditions
After superheat is adjusted, it is recommended that the
subcooling be checked at the condenser coil liquid line out. In
most operating conditions, 10ºF to 15ºF of sub-cooling is
Outside Air Into Return Duct
Do not introduce cold outside air into the return duct of a heat
pump installation. Do not allow air entering the indoor coil to
drop below 65°F (18ºC). Air below this temperature will cause
low discharge pressure, thus low suction pressure, and
excessive defrost cycling resulting in low heating output. It
may also cause false defrosting.
An undercharged heat pump on the heating cycle will cause
low discharge pressure resulting in low suction pressure and
frost accumulation on the outdoor coil.
Poor "Terminating" Sensor Contact
The defrost terminating sensor must make good thermal
contact with the outdoor coil tubing. Poor contact may not
terminate the defrost cycle quickly enough to prevent the unit
from cutting out on high discharge pressure.
Malfunctioning Reversing Valve
This may be due to:
1. Solenoid not energized—In order to determine if the
solenoid is energized, touch the nut that holds the
solenoid cover in place with a screwdriver. If the nut
magnetically holds the screwdriver, the solenoid is
energized and the unit is in the cooling cycle.
2. No voltage at the solenoid—Check unit voltage. If no
voltage, check wiring circuit.
3. Valve will not shift—If the unit is undercharged, check for
leaks. If valve body damaged, replace valve. If unit is
properly charged, and it is on the heating cycle, raise the
discharge pressure by restricting airflow through the
indoor coil. If the valve does not shift, tap it lightly on both
ends with a screwdriver handle.
NOTE: Do not tap the valve body.
If the unit is on the cooling cycle, raise the discharge
pressure by restricting airflow through the outdoor coil. If
the valve does not shift after the above attempts, turn off
the unit and wait until the discharge and suction pressure
equalize, and repeat above steps. If the valve does not
shift, replace it.