Symptoms Of A Restriction - Fisher & Paykel RX256DT4X1 FP Service Manual

321023
• Depending on the amount of the shortage, the condenser will not be hot, but closer to room
temperature. The capillary tube will be warmer than normal from a slight shortage.
• If the leak is on the high side of the system, both gauges will show lower than normal readings and
will show progressively lower readings as this charge becomes less. The suction pressure gauge
will probably indicate a vacuum.
• If the leak is on the low side of the system, the suction pressure gauge will be lower than normal
(probably in a vacuum) and the head pressure gauge will be higher than normal. It will probably
continue to become higher because air drawn in through the leak is compressed by the compressor
and accumulates in the high side (condenser) of the system.
• Only partial frosting of evaporator instead of even frosting of entire coil.
Usually the first thing that is noticed by the user is a rise in food temperatures.
NOTE 1:
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 meat keeper 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.
12.3

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
backpressure, head pressure, and wattage, warmer product temperatures.
If a total restriction is on the discharge side of the compressor, higher than normal head
NOTE 2:
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.
3. moisture in system.
88