74 PB
R-410A SEALED SYSTEM REPAIR
Undercharged Refrigerant Systems
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 undercharge 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
insufcient 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 amperage drawn by the compressor motor should show a lower reading. (Check the Unit
Specication.) After the unit has run 10 to 15 minutes, check the gauge pressures. Gauges connected to system
with an undercharge will have low head pressures and substantially low suction pressures.
Figure 505(Undercharged System)
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