System Diagnosis
34
©2007 Viking Preferred Service
Symptoms of a Restriction
Always remember refrigeration (cooling) occurs on the
low pressure side of a partial restriction (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:
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.
