Friedrich Q Series Service & Parts Manual page 44

R-410A SEALED SYSTEM REPAIRS
HIGH PRESSURE HAZARD
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.
RISK OF ELECTRIC SHOCK
Unplug and/or disconnect all electrical power
to the unit before performing inspections,
maintenances or service.
Failure to do so could result in electric shock,
serious injury or death.
Figure 601 (Undercharged System)
44
WARNING
WARNING
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.
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.