Page 29
D - Compressor Controls
See unit wiring diagram to determine which controls are
used in each unit. Optional controls are identified on
wiring diagrams by arrows at junction points.
1- Freezestat (S49)
Switch de-energizes compressor when indoor coil
temperature falls below 29
F (-2
C) to prevent coil
freeze-up. Switch resets when indoor coil
temperature reaches 58
F (15
C).
2- High Pressure Switch (S4)
Auto-reset switch is located on the discharge line.
Switch opens at 640 psig and closes at 475 psig.
Switch is wired directly into the defrost control
(CMC1), which provides a 5 strike lockout feature.
3- Defrost Switch (S6)
100269 Series
Only
Defrost switch closes to initiate defrost when liquid
line temperature falls to 42
°
F (5.6
°
C). Defrost switch
opens when liquid line temperature reaches 70
°
F
(21
°
C) to terminate defrost. If the liquid line
temperature does not rise above 70
°
F (21
°
C), the
CMC1 will terminate defrost after 14 minutes. The
defrost switch is located on the liquid line between the
outdoor expansion valve and the distributor
4- Ambient and Coil Temperature Sensors (RT13, RT21)
100135 Series Only
Both sensors provide input to the defrost control
which cycles defrost. The ambient sensor is located
on the inside of the corner mullion on the back of the
outdoor coil section. The coil sensor is located on a
return bend on the front of the outdoor coil.
5- Defrost Controls (CMC1)
Gas heat is energized during defrost to maintain
discharge air temperature.
100269 Series Time/Temperature
When the liquid line temperature drops below 42°F
(5.6
°
C), the defrost switch closes and signals the
defrost control that a defrost cycle is needed. If the
defrost switch is still closed after 90 minutes (default),
a defrost cycle begins and operates for 14 minutes.
The defrost switch can terminate the defrost cycle
before the 14 minutes elapses if liquid line
temperature reaches 70
°
F (21
°
C).
Note - The defrost control will not energize a defrost cycle
unless the unit has been operating in heating mode for an
accumulated 90 minutes (default) on 100269 series
boards. The run time interval can be changed by moving
the jumper on the CMC board timing pins. See figure 20.
The defrost interval can be adjusted to 30, 60, or 90
minutes. If the timing selector jumper is not in place, the
control defaults to a 90-minute defrost interval.
DEFROST CONTROL BOARD CMC1
FIGURE 20
DIAGNOSTIC
LEDS
100269 SERIES:REMOVED
AT THE FACTORY TO DIS
ABLE COMPRESSOR DELAY
TIMING JUMPER:
100269 SERIES: 90 MINUTES
