System Diagnosis
32
©2007 Viking Preferred Service
CONDITION
SUCTION
PRESSURE
VARIATION
FROM
NORMAL
HEAD
PRESSURE
VARIATION
FROM
NORMAL
T1 INLET
TEMPERATURE
VARIATION
FROM NORMAL
T2 OUTLET
TEMPERATURE
VARIATION FROM
NORMAL
T3 SUCTION
TEMPERATURE
VARIATION
FROM NORMAL
WATTAGE
VARIATION
FROM
NORMAL
Refrigerant
Overcharge
Increase Increase
Warmer
Warmer
Colder
Increase
Shortage of
Refrigerant
Decrease
Decrease or
Increase See
Text
Colder Warmer Warmer
Decrease
Partial
Restriction
Decrease
Decrease or
Increase See
Text
Colder Warmer Warmer
Decrease
Air in System Near Normal
Increase
Warmer Warmer Warmer
Increase
Low Ambient
Installations
(High
Ambients the
Reverse)
Decrease Decrease
Colder Warmer Warmer
Decrease
Additional
Heat Load
Increase
Increase
Warmer Warmer Warmer
Increase
Inefficient
Compressor
Increase
Normal or
Decrease
Warmer or
Colder
Warmer Warmer
Decrease
Symptoms of an Overcharge
Above normal freezer temperatures.
Longer than normal or continuous run.
Freezing in refrigerator, especially on forced air
meatkeeper models.
Higher than normal suction and head pressure.
Higher than normal wattage.
Evaporator inlet and outlet temperatures warmer than
normal.
Suction tube temperature below ambient. Always check
for separated heat exchanger when suction temperature
is colder than ambient.
Various conditions could indicate an overcharge. For
example, if the cooling coil is not defrosted at regular
intervals, due to a failure of the defrost system, the
refrigerant will "flood out" and cause the suction line to
frost or sweat. The cause of this problem should be
corrected rather than to purge refrigerant from the
system. Running the freezer section colder than
necessary (-2 to -1°F is considered normal package
temperatures) or continuous running of the compressor
for a variety of reasons, or the freezer fan motor not
running, may give the indication of an overcharge.
Symptoms of Air in System
This can result from a low side leak or improper
servicing. If a leak should occur on the low side, the
temperature control would not be satisfied; thus,
continuous running of the compressor would result. The
compressor would eventually pump the low side into a
vacuum drawing air and moisture into the system. Air
and R134A do not mix so the air pressure would be
added to the normal head pressure, resulting in higher
than normal head pressures.
One way to determine if air is in the system is to read
the head pressure gauge with the product off and
evaporator and condenser at the same temperature and
then take the temperature on the condenser outlet tube.
This temperature should be within 3° or 4°F of what the
Pressure-Temperature Relation chart shows for the
given idle head pressure. If the temperature of the
condenser outlet is considerably lower than the idle
head pressure of the gauge this would indicate there is
air in the system.
Thorough leak checking is necessary. Correct the
source of the leak. Do not attempt to purge off the air
because this could result in the system being
undercharged. It is best to discharge, replace drier,
evacuate and recharge with the specified refrigerant
charge.
