Thermo King 914970, Manual

Page: 115 / 186

115
Refrigeration Maintenance
Evacuation
Evacuation is Important and is Critical to System
Performance!
It has been determined through testing and system
analysis that refrigeration systems which contain
non-condensables such as nitrogen and/or air can
be overcharged with refrigerant when charged
using the sight glass method. An overcharge 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 evacuation
using the proper tools and procedures. (See
attached tool 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 evacuation to prevent
trapping of refrigerant or non-condensables.
• 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 System (see Tool Catalog).
However, the principles of 3-point evacuation
and the use of a micron gauge during
evacuation should always be practiced.
See the diagram of the Thermo King Evacuation
Station 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
evacuation. 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
evacuation. 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
evacuation. When closed, V-4 isolates the
evacuation hoses and the unit from the evacuation
system.