SERVICING
82
S-113 OVERCHARGE OF REFRIGERANT
An overcharge of refrigerant is normally indicated by an
excessively high head pressure.
An evaporator coil, using an expansion valve metering device,
will basically modulate and control a flooded evaporator and
prevent liquid return to the compressor.
An evaporator coil, using a capillary tube metering device,
could allow refrigerant to return to the compressor under
extreme overcharge conditions. Also with a capillary tube
metering device, extreme cases of insufficient indoor air can
cause icing of the indoor coil and liquid return to the
compressor, but the head pressure would be lower.
There are other causes for high head pressure which may
be found in the "Service Problem Analysis Guide."
If other causes check out normal, an overcharge or a system
containing non-condensables would be indicated.
If this system is observed:
1. Start the system.
2. Remove and capture small quantities of gas from the
suction line dill valve until the head pressure is reduced
to normal.
3. Observe the system while running a cooling performance
test. If a shortage of refrigerant is indicated, then the
system contains non-condensables.
S-114 NON-CONDENSABLES
If non-condensables are suspected, shut down the system
and allow the pressures to equalize. Wait at least 15
minutes. Compare the pressure to the temperature of the
coldest coil since this is where most of the refrigerant will be.
If the pressure indicates a higher temperature than that of the
coil temperature, non-condensables are present.
Non-condensables are removed from the system by first
removing the refrigerant charge, replacing and/or installing
liquid line drier, evacuating and recharging.
CHECKING COMPRESSOR EFFICIENCY
The reason for compressor inefficiency is broken or dam-
aged scroll flanks on Scroll compressors, reducing the ability
of the compressor to pump refrigerant vapor. The condition
of the scroll flanks is checked in the following manner.
1. Attach gauges to the high and low side of the system.
2. Start the system and run a “Cooling Performance Test. If
the test shows:
a. Below normal high side pressure.
b. Above normal low side pressure.
c. Low temperature difference across coil.
d. Low amp draw at compressor.
And the charge is correct. The compressor is faulty
– replace the compressor.
