Refrigeration Maintenance (Rev. 04/03)
61
Evacuation is Important and is Critical to
System Performance!
It has been determined through testing and system analysis
that refrigeration systems which contain non-condensable
such as nitrogen and/or air can be overcharged with refrig-
erant when charged using the sight glass method. An over-
charge of refrigerant will cause compressor damage.
Therefore, Thermo King recommends that all repairs to the
refrigeration system include the removal and reclamation
(cleaning) of the refrigerant, followed by a thorough evacu-
ation using the proper tools and procedures. (See attached
too list and evacuation procedures.)
The primary objective of evacuation is to bring the system’s
pressure to a low micron level to ensure the removal of
moisture and non-condensables. There are however, certain
other principles which must be observed. These are:
• Evacuate from 3-points to access both sides of check
valves and solenoids. Energize solenoids during evacu-
ation to prevent trapping of refrigerant or non-condens-
ables.
• Always leave service valve caps on during evacuation
and do not exercise the valve stems while the unit is in
a deep vacuum. Packing glands on older valves are
prone to leak.
• Never attempt evacuation without a micron or vacuum
gauge. The micron gauge will help determine:
a. If the pump is capable of pulling a deep vacuum.
b. When the vacuum pump oil is contaminated.
c. If the vacuum hoses and valves are leak free.
d. If the unit is leak free.
e. How long you should evacuate the unit.
f. That the unit is still in a deep vacuum before any
lines are disconnected or refrigerant is added.
NOTE: The attached evacuation procedures have been
written to be used with the Thermo King Evacuation Sys-
tem (Tool No. 204-725). However, the principles of 3-point
evacuation and the use of a micron gauge during evacua-
tion should always be practiced.
Refer to the diagram of the Thermo King evacuation station
(Tool No. 204-725) and note the location of the valves.
Valve #1 (V-1): Is in the open position when the pump is
running to evacuate the hoses and/or the unit. When V-1 is
closed, the pump has been isolated from the hoses and/or
the unit.
Valve #2 (V-2): Is in the open position during unit evacua-
tion. In the closed position, V-2 isolates the micron gauge
and thermistor assembly from the hoses and/or the unit.
Valve #3 (V-3): Is in the open position during unit evacua-
tion. When closed, V-3 isolates the micron gauge and the
vacuum pump from the other evacuation hoses.
Valve #4 (V-4): Is in the open position during unit evacua-
tion. When closed, V-4 isolates the evacuation hoses and
the unit from the evacuation system.
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