21
16021730 Rev. 0
System Diagnosis
the high side (condenser) of the system.
Only partial frosting of evaporator instead of even
frosting of entire coil.
NOTE 1
:
Usually the first thing that is noticed by the
user is a rise in temperature foods. Although
temperatures will rise in both the freezer section
and the food compartment, the frozen meats
and vegetables will not thaw immediately. The
customer doesn't associate the problem with
the freezer section and will first notice that milk
and other food beverages are not cold enough.
Under some circumstances, such as in the case of
forced air meatkeeper model with a slight shortage of
refrigerant, freezing in the food compartment may be
experienced due to the additional running time. With a
refrigerant leak, however, it always gets worse and as
the refrigerant charge decreases the temperature will
continue to rise.
With a shortage of refrigerant the capillary line will not
have a full column of liquid. As a result, there is a
noticeable hissing sound in the evaporator. This should
not be mistaken for the regular refrigerant boiling
sounds that would be considered normal.
Symptoms of a Restriction
Always remember refrigeration (cooling) occurs on the
low pressure side of a partial restriction (obviously a
total restriction will completely stop the circulation of
refrigerant and no cooling will take place).
Physically feel the refrigeration lines when a restriction
is suspected. The most common place for a restriction
is at the drier-filter or at the capillary tube inlet or outlet.
If the restriction is not total there will be a temperature
difference at the point of restriction, the area on the
evaporator side will be cooler. In many cases frost and/
or condensation will be present. A longer time is
required for the system to equalize.
Any kinked line will cause a restriction so the entire
system should be visually checked.
A slight restriction will give the same indications as a
refrigerant shortage with lower than normal back
pressure, head pressure, and wattage, warmer product
temperatures.
NOTE 2:
If a total restriction is on the discharge side of
the compressor, higher than normal head
pressures and wattages would result. This is
true only while the low side is being pumped out
and if the restriction was between the
compressor and the first half of the condenser.
To diagnose for a restriction versus a refrigerant
shortage, discharge the system, replace the drier-filter,
evacuate and recharge with the specified refrigerant
charge. If the unit performs normally three possibilities
exist: 1) refrigerant loss, 2) partially restricted drier-
filter, and 3) moisture in system.
If the unit performs as it previously did you may have a
restricted capillary line or condenser or kinked line.
Find the point of restriction and correct it.
A restriction reduces the flow rate of the refrigerant and
consequently reduces the rate of heat removal.
Complete restriction may be caused by moisture, solid
contaminants in the system, or a poorly soldered joint.
Moisture freezes at the evaporator inlet end of the
capillary tube or solid contaminants collect in the drier-
filter. The wattage drops because the compressor is not
circulating the usual amount of refrigerant.
As far as pressure readings are concerned, if the
restriction, such as a kinked line or a joint soldered shut
is anywhere on the low side, the suction pressure would
probably be in a vacuum while the head pressure will be
near normal. If the restriction is on the high side, the
suction pressure, again, will probably be in a vacuum
while the head pressure will be higher than normal
during the pump out period described earlier. In either
case, it will take longer than the normal ten minutes or
so for the head pressure to equalize with the low side
after the compressor stops.
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.
