35
Service Procedures
To avoid risk of electrical shock, personal injury, or death, disconnect electrical power
source to unit and discharge capacitor through resistor before attempting to service, unless
test procedures require power to be connected. Ensure all ground wires are connected
before certifying u nit as repaired and / or operational
Dehydrating Sealed Refrigeration System
Moisture in a refrigerator sealed system exposed to
heat generated by the compressor and motor reacts
chemically with refrigerant and oil in the system and
forms corrosive hydrochloric and hydrofluoric acids.
These acids contribute to the breakdown of motor
winding insulation and corrosion of compressor
working parts, causing compressor failure.
In addition, sludge, a residue of the chemical
reaction, coats all surfaces of sealed system, and will
eventually restrict refrigerant flow through capillary
tube.
To dehydrate sealed system. Evacuate system (see
paragraph
Evacuation
).
Leak Testing
To prevent serious injury or
death from violent
explosions, NEVER use
oxygen or acetylene for pressure testing or clean
out of refrigeration systems. Free oxygen will
explode on contact with oil. Acetylene will
explode spontaneously when put under pressure.
It is important to check sealed system for refrigerant
leaks. Undetected leaks can lead to repeated service
calls and eventually result in system contamination,
restrictions, and premature compressor failure.
Refrigerant leaks are best detected with halide or
electronic leak detectors.
Testing Systems Containing a Refrigerant Charge
1.
Stop the operation (turn refrigerator off.)
2.
Holding leak detector exploring tube as close to
system tubing as possible, check all piping,
joints, and fittings.
NOTE:
Use soap suds on areas leak detector cannot
reach or reliable test.
Testing Systems Containing No Refrigerant Charge
1. Connect cylinder of nitrogen, through gauge
manifold, to process tube of compressor and
liquid line strainer.
2. Open valves on nitrogen cylinder and gauge
manifold. Allow pressure to build within sealed
system.
3. Check for leaks using soap suds.
If leak is detected in tubing, replace tubing. If leak is
detected in either coil, replace faulty coil.
Restrictions (Symptoms)
Restrictions in sealed system most often occur at
capillary tube or filter drier, but can exist anywhere
on liquid side of system.
Restrictions reduce refrigerant flow rate and heat
removal rate. Wattage drops because compressor is
not circulating normal amount of refrigeration.
Common causes of total restrictions are moisture,
poorly soldered joints, or solid contaminants.
Moisture freezes at evaporator inlet end of capillary
tube. Solid contaminants collect in filter drier.
If restriction is on low side, suction pressure will be
in a vacuum and head pressure will be near normal.
If restriction is on high side, suction pressure will be
in a vacuum and head pressure will be higher than
normal during pump out cycle.
Refrigeration occurs on low pressure side of partial
restriction. There will be a temperature difference at
the point of restriction. Frost and /or condensation
will be present in most cases at the point of
restriction. Also system requires longer to equalize.
Slight or partial restriction can give the same
symptoms as refrigerant shortage including lower
than normal back pressure, head pressure, wattage,
and warmer temperatures.
Total restriction on the discharge side of compressor
when restriction is between compressor ands first half
of condenser results in higher than normal head
pressure and wattage while low side is being pumped
out.
Testing for Restrictions
To determine if a restriction exists:
1.
Attach gauge and manifold between suction and
discharge sides of sealed system.
2.
Turn unit on and allow pressure on each side to
stabilize. Inspect condenser side of system.
Tubing on condenser should be warm and
temperature should be equal throughout (no
sudden drops at any point along tubing.)
