accumulation of frost. Where possible, check the capillary tube and straighten any kinks to
relieve the restrictions. Check the unit operation. If the condition persists, replace the defective
part. If the freeze-up condition does not exist and there is not a kink, you can assume that a
foreign particle is causing the restrictions. The only remedy in this case is to replace the
restricted part.
(2) - Partial Restriction In Low Side Tubing
Bent tubing, foreign matter, or moisture in the system may cause a partial restriction in the low
side tubing. This is usually indicated by frost-free tubing between the restriction and the capillary
tube and by frost-covered tubing between the restriction and the suction line. The restriction acts
like a second capillary tube, increasing the pressure ahead of it (warming) and decreasing the
pressure beyond it (cooling). To confirm the existence of a restriction in the low side tubing,
perform operational pressure checks.
(3) - Slow Leak In System
On forced air models, long run time will be noticed during the early stages of a leak. As the
refrigerant continues to escape, the compartment will gradually warm up and the compressor will
run continuously.
(4) - Incorrect Refrigerant Charge
The sealed unit may have too much refrigerant (overcharged system) or too little refrigerant
(undercharged system). The troubleshooting guide will inform you on how to recognize a system
with these defects.
An overcharged system may have a frost back condition appearing on the suction line. When the
compressor stops, the frost melts and drips on the floor. A heat exchanger separation will also
cause this symptom.
An undercharged system, depending on the degree of undercharge, will operate with
temperatures above normal and the compressor run time will be increased. The greater the
undercharge, the higher the temperature will be and the longer the run time. An undercharged
system must be purged, evacuated, and recharged with the proper amount of refrigerant.
Before recharging, test for refrigerant leaks.
3.7 LEAK TESTING
Once it has been determined through proper diagnosis that a leak is present in the sealed
system, attempt to find the leak before opening the system if possible. To check the high side for
leaks, be sure that the compressor is running. During run time the high side pressure is greater.
To increase the pressure slightly, stop the condenser fan blade or block the air flow through the
condenser. To check the low side for leaks, stop the compressor. During off times, the low side
pressure will increase to equalize with the high side. By warming the evaporator, this pressure
will increase. If too much refrigerant has leaked out to create enough pressure to locate the leak,
add 2 ounces of the proper refrigerant to the system and proceed with the test procedure.
The presence of oil around a tubing joint usually indicates a leak. Care must still be taken to
pinpoint the exact location. Remember that a leak detector compatible with R134A refrigerant
must be used. A sealed system component, such as the evaporator or hot pipe, should not be
condemned unless a non-repairable leak is confirmed. This should be determined by either
locating the actual leak or by isolating the component from the rest of the system and
determining if it holds pressurization or a vacuum - whichever method is chosen.