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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. Noncon-
densables can also cause these symptoms. To confi rm,
remove some of the charge, if conditions improve, system
may be overcharged. If conditions don’t improve, Noncon-
densables 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 cont’d