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 TM 55-1905-220-14-8
4-29. AIR CONDITIONING SYSTEM - MAINTENANCE INSTRUCTIONS (Continued).
NOTE
To check the settings of a low limit or safety thermostat, such
as used for a water chiller, it may be necessary to bypass the
operating thermostat and the compressor low pressure control
switch.
n. Water Pressure Failure Control Switch.
(1) Operation.
The safety function of the water pressure failure switch is described in paragraph 4-29a(20). The water
pressure failure switch is similar in construction and operation to the low pressure control switch shown below
and described in paragraph 4-29k.
(2) Adjustment.
Set the water pressure failure switch to cut-in at 15 psig (103.4 kPa) and cut out at 5 psig (34.5 kPa).
Proceed as follows:
(a) Turn differential adjusting screw counterclockwise to minimum limit.
(b) Turn range screw clockwise to high limit.
(c) Throttle water valves until condenser water supply pressure is 15 psig (103.4 kPa). Turn
range screw slowly counterclockwise until contacts just close. This fixes the cut-in point.
(d) Slowly throttle condenser water supply decreasing pressure. Switch contacts should open at
5 psig (34.5 kPa). If switch contacts open above 5 psig (34.5 kPa), turn differential screw clockwise to widen
differential slightly.
(e) Control condenser water supply and check switch settings.
o. Pressure and Leak Test.
(1) The entire refrigerant piping system should be tested for leaks at a pressure of 150 psig (1034 kPa).
The high pressure side of the system should be tested at 225 psig (1551 kPa).
(2) To build up pressure, use a refrigerant or a dry stable gas such as nitrogen. When using dry
nitrogen, guard against building up dangerous pressures in the system. It is advisable to use pressure reducing
valves on gas cylinders.
4-893
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