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 TM 55-1905-220-14-8
4-29. 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 5 (-16.7 to -15 ) with changes in range adjustment. On the high end of the thermostat
F
C
temperature range it will be about 2 (-16.7 ) on the low end of the range it will be 5 (-15 ). )
F
C
F
C
(c)
Thermostat recommended set points are given in paragraph 4-29-1-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 counterclockwise until
contacts just close. This fixes the cut-in point.
4
Lower the compartment or other medium being cooled to cutout temperature, then turn
differential screw counterclockwise 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-
29-1-s, set differential at a minimum (2 to -5 (-16.7 to -
F
20.6 ) and adjust range so that desired temperature of
C
medium being cooled is half-way between cut-in and cut-out
points. For example, if a space is to be maintained at 20 (-
F
6.7 ), and minimum differential obtained is 4 (-15.6 ), set
C
F
C
the thermostat to cut-in at 22 (-5.6 ) and cut-out at 18 (-
F
C
F
7.8 ).
C
5 Allow system to stabilize and observe thermostat settings during an operating cycle.
4-892
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