Friedrich 9 - Manual (Page 30)

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 insufficient 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.
overcharged Refrigerant Systems
A check of the amperage drawn by the compressor
motor should show a lower reading. (Check the Unit
Specification.) 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.
of the evaporator will not be encountered because the
refrigerant will boil later if at all. Gauges connected to
system will usually have higher head pressure (depending
upon amount of over charge). Suction pressure should be
slightly higher.
Compressor amps will be near normal or higher.
Noncondensables can also cause these symptoms. To
confirm, remove some of the charge, if conditions improve,
system may be overcharged. If conditions don’t improve,
Noncondensables are indicated.
Whenever an overcharged system is indicated, always
make sure that the problem is not caused by air flow
problems. Improper air flow over the evaporator coil may
indicate some of the same symptoms as an over charged
system.
An overcharge 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
ELECTRIC SHOCK HAZARD
WARNING
Turn off electric power before service or
installation.
Extreme care must be used, if it becomes
necessary to work on equipment with power
applied.
Failure to do so could result in serious injury or
death.
Sealed Refrigeration System contains refrigerant
and oil under high pressure.
Proper safety procedures must be followed,
and proper protective clothing must be worn
when working with refrigerants.
Failure to follow these procedures could
result in serious injury or death.
WARNING
HIGH PRESSURE HAZARD
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