Thermo King 914 724, Manual

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Unit Description (Rev. 1/99)
9
does not. The heat relay also energizes the optional water
pump and hot water valve, or the optional heater contactor.
Defrost
The defrost cycle can be initiated any time the evaporator
coil temperature is below 42 F (5.6 C). Defrost is initiated
automatically by the defrost timer, or manually by pressing
the Manual Defrost switch.
The defrost relay energizes the compressor clutch (or motor
contactor) and the 26 circuit to route hot refrigerant gas to
the evaporator. The defrost relay also interrupts power to the
fan relay to stop the evaporator and condenser fans during
defrost. The defrost cycle will continue until the evaporator
coil temperature rises to 52 F (11.1 C), causing the defrost
termination switch to open, which terminates the defrost
cycle. If the defrost termination switch does not open in less
than 45 minutes, the defrost timer will terminate the defrost
cycle 45 minutes after is was started.
OPERATING MODES
• Cool—Above setpoint when the temperature is drop-
ping. More than 2 ± 1 F (1 ± 0.5 C) above setpoint
when the temperature is rising.
• Null—Between setpoint and 2 ± 1 F (1 ± 0.5 C) below
setpoint when the temperature is dropping. Between
setpoint and 2 ± 1 F (1 ± 0.5 C) above setpoint when
the temperature is rising.
• Heat—More than 2 ± 1 F (1 ± 0.5 C) below setpoint
when the temperature is dropping. Below setpoint when
the temperature is rising (optional).
• Defrost—Initiated manually or automatically at evapo-
rator temperatures below 42 F (5.6 C). Terminated
when the evaporator temperature rises to 52 F (11.1 C),
or 45 minutes after initiated.
0. Setpoint
1. Cool
2. Null
3. Heat* (Optional)
*Heat lockout occurs at setpoints of
15 F (-9.5 C) or lower.
Thermostat Algorithm
A
G
A3
0
1