Despatch 926E Equipment Manual (C-155)Rev 2/11 - Manual (Page 25)

20
Cooling Operation
Cooling operations with the chamber are essentially the same as those for heating
operations. Refer to the manufacturers controller instructions to familiarize yourself with
the operation of this control.
1.
Attach the test fixture or tray to the chamber.
2.
Insure that the POWER switch is off.
3.
Connect LN
2
supply.
4.
Turn on supply valve.
5.
Plug in the chamber power cord to the correct line power. Avoid adapters that
will either unground the chamber or will permit connecting to the wrong power
source. Check current rating of circuit.
6.
Turn the POWER switch ON and allow the chamber to cool to the correct
operating temperature. The HI-LIMIT control is not used during cooling
operations.
7.
Set the SET-POINT to the desired temperature.
A relief port has been included in the chamber to protect against excessive internal
pressure.
The cooling system will operate efficiently only when there is no vapor lock in the
coolant line. Vapor locks can be reduced by keeping the coolant cylinders and lines at
the same temperature or by preventing the coolant lines from passing through areas of
much higher temperature. It is also a good practice to keep the coolant lines as short
as possible.
When the chamber is not in use, or when it is used for other than low temperature tests,
the valves of the coolant cylinder(s) should be closed to prevent leakage.
After long periods of operation at low temperatures, a certain amount of moisture
condenses inside the chamber in the form of snow and frost. Although the insulation in
the test chamber is sealed against both internal and external accumulation of moisture,
some moisture will eventually collect in the fiberglass insulation. The resulting loss in
insulation efficiency tends to decrease cooling rate and increase coolant consumption.