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 TM 55-1905-219-14-8
4-28. AIR CONDITIONING SYSTEM - MAINTENANCE INSTRUCTIONS (Continued).
(3) Adjustment.
(a) The thermostat cut-in and cut-out points are adjustable within the operating range. The range
adjustment screw changes both the cut-in and cut-out points by an equal amount. Turning range screw
clockwise raises both set points and turning it counterclockwise lowers both set points.
(b) The differential adjustment governs the cut-out point but does not affect the cut-in point. Turning
the differential adjustment screw clockwise widens the differential. (The minimum differential will vary from 2
to 5F (-16.7to -15C) with changes in range adjustment. On the high end of the thermostat temperature
range it will be about 2F (-16.7C) on the low end of the range it will be 5F (-15C) . )
(c) Thermostat recommended set points are given in paragraph 4-28-1-s. To set a thermostat proceed
as follows:
1 Turn differential screw clockwise to wide limit.
2 Turn range screw counterclockwise to low limit.
3 Bring the compartment or other medium being cooled to cut-in temperature and turn range screw
clockwise until contacts open; then turn range screw slowly counterclock-wise until contacts just
close. This fixes the cut-in point.
4 Lower the compartment or other medium being cooled to cut-out temperature, then turn differential
screw counter-clockwise until contacts open. This fixes the cut-out point.
NOTE
As a general rule, if an operating thermostat is to be reset to maintain a temperature other than as
specified in paragraph 4-28-1-s, set differential at a minimum (2 to -5F (-16.7 to -20.6C) and
adjust range so that desired temperature of medium being cooled is half-way between cut-in and cut-
out points. For example, if a space is to be maintained at 2F (-6.7 ), and minimum differential
C
obtained is 4F (-15.6C), set the thermostat to cut-in at 22F (-5.6C) and cut-out at 18F (-
7.8 ).
C
5 Allow system to stabilize and observe thermostat settings during an operating cycle.
4-862
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