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An undercharged system will result in poor performance (low
pressures, etc.) in both the heating and cooling cycle.
Whenever you service a unit with an under charge of refrigerant,
always suspect a leak. The leak must be repaired before charging
the unit.
To check for an undercharged system, turn the unit on, allow the
compressor to run long enough to establish working pressures in
the system (15 to 20 minutes).
During the cooling cycle you can listen carefully at the exit of the
metering device into the evaporator; an intermittent hissing and
gurgling sound indicates a low refrigerant charge. Intermittent
frosting and thawing of the evaporator is another indication of a
low charge, however, frosting and thawing can also be caused by
insuffi cient air over the evaporator.
Checks for an undercharged system can be made at the compressor
. If the compressor seems quieter than normal, it is an indication of
a low refrigerant charge. A check of the amper age drawn by the
compressor motor should show a lower reading. (Check the Unit
Specifi cation.) After the unit has run 10 to 15 minutes, check the
gauge pressures.
Gauges connected to system with an under charge will have low
head pressures and substantially low suction pressures.
UNDERCHARGED REFRIGERANT SYSTEMS
NOTE: Heat pump
refrigeration
drawing
OVERCHARGED REFRIGERANT SYSTEMS
Compressor amps will be near normal or higher. Noncondensables
can also cause these symptoms. To confi rm, remove some of the
charge, if conditions improve, system may be overcharged. If condi-
tions don’t improve, Noncondensables are indicated.
Whenever an overcharged system is indi cated, always make sure
that the problem is not caused by air fl ow problems. Improper
air fl ow over the evaporator coil may indicate some of the same
symptoms as an overcharged system.
An over charge can cause the compressor to fail, since it would
be “slugged” with liquid refrigerant.
The charge for any system is critical. When the compressor is noisy,
suspect an overcharge, when you are sure that the air quantity over
the evaporator coil is correct. Icing of the evapora tor will not be
encountered because the refriger ant will boil later if at all. Gauges
connected to system will usually have higher head pressure
(depending upon amount of overcharge). Suction pressure should
be slightly higher.
Refrigerant Charging