amount of refrigerant which will show up as a leak. Do
not be quick to condemn the cabinet as a leaker. Let the
cabinet air out for a few minutes, then make another
leak test being careful not to pull on the tubing entering
the insulated area as other cells may be opened.
Proceed in a normal manner for leak testing a system.
To check a cabinet with a suspected internal leak:
1. Install service taps on both high and low side of sys-
tem.
2. Reclaim all refrigerant in system.
3. Refer to page 14 to isolate evaporator from con-
denser, compressor, etc.
4. Pressurize each section with 250 pounds of dry nitro-
gen and install gauges.
5. Let the cabinet sit overnight to see which section
loses pressure. In most cases, any leaks found will be
in unit compartment area.
UNDERCHARGE OF REFRIGERANT
An undercharge of refrigerant caused by a refrigerant
leak or by improper installation of a replacement
compressor will result in a lower than normal suction
pressure, excessive or continuous operation of the
compressor or higher than normal cabinet temperature.
When a system has a normal refrigerant charge the
operating suction pressure will be shown on pages 29-
35. Also the suction line entering the compressor will be
slightly cooler than room temperature.
ADDING REFRIGERANT
CAUTION
Always introduce refrigerant in a vapor state into
the system.
When a system shows by its operating characteristics to
be short of refrigerant, it must be assumed that there is
a leak somewhere in the system. Proceed to check the
system with a leak detector. When the leak is located, it
should be repaired if it is a repairable leak. Any
repairable leak will occur as a broken tube, or possibly a
loose flare fitting in the machinery compartment.
Unless the system has lost most of its refrigerant
charge, the leak test can be made without the addition
of extra refrigerant. If the system is completely void of
gas, then a sufficient refrigerant charge must be added
to make a leak test, and the system must be complete-
ly evacuated and recharged.
COMPLETE RECHARGE
OF REFRIGERANT
Give the system a complete recharge of refrigerant in
case of a major refrigerant leak; one that is repairable,
such as a broken tube or a cracked flare connection
occurring in the machine compartment.
If such a leak should occur, the unit will run, but with par-
tial or no refrigerant and the operating pressures are
usually low enough and below atmospheric pressure so
that with a leak on the low side, air and moisture are
drawn into the system.
If there is any reason to believe the system contains
moisture, the low side and high side should be evacuat-
ed and a new filter drier installed. Charge should be
weighed in.
OVERCHARGE OF REFRIGERANT
When the cabinet is pulled down to temperature, an indi-
cation of an overcharge is that the suction line will be
cooler than normal and may frost up. The normal tem-
perature of the suction will be a few degrees cooler than
room temperature. If its temperature is much lower than
room temperature, the unit will run longer because the
liquid is pulled beyond the accumulator into the heat
exchanger. When the overcharge is excessive, the suc-
tion line will sweat or frost. Purge any excess refrigerant
into a reclaimer. Purge carefully so that system does not
become undercharged.
COMPRESSOR MOTOR BURNED OUT
There are four major causes of motor burn out:
1. LOW LINE VOLTAGE
2. LOSS OF REFRIGERANT
3. HIGH HEAD PRESSURE
4. MOISTURE
1. LOW LINE VOLTAGE
When the motor winding in a compressor gets too hot
the insulation melts and the winding short circuits. A
blackened, burned out run or start winding is the result.
Low line voltage causes the winding to get very hot
because it is forced to carry the current at the same
compressor load. When this current gets too high or is
carried for too many hours, the motor run windings fail.
A burn out caused by low voltage is generally a slow
burn out, and contaminates the system.
2. LOSS OF REFRIGERANT
A second cause of motor burn out is loss of refrigerant.
In a hermetically sealed compressor the refrigerant
vapor passes down around the motor winding. The cool
refrigerant vapor keeps the motor operating at the prop-
er temperature. If there is a refrigerant leak and there is
little or no cooling of the motor, the windings become too
hot and a burn out will result. The overload protector
may not always protect against this type of burn out,
since it requires the transfer of high heat from the motor
through the refrigerant vapor to the compressor dome.
18
GENERAL OPERATIONS
