Unit Description
34
information is used by the microprocessor and
software to determine the unit operating
conditions.
The following valves are required for each zone.
They are located in the remote evaporator(s) for
each zone.
• Liquid Line Solenoid - This valve is
energized (open) any time cooling, heating or
defrosting is required in its zone. The valve is
de-energized when the zone is in null to stop
refrigerant flow in that zone. This is a
normally closed valve.
• Hot Gas Solenoid - This valve is energized
(open) any time heating or defrosting is
required in the zone. This is a normally closed
valve.
• Suction Line Solenoid - If a zone is capable
of reverse cycle operation it is said to be
invertible. Reverse cycle means that the
evaporator coil in that zone is used as the
condenser coil during heat operation as long
as at least one other zone is operating in cool
mode.
The suction line solenoid is energized (closed)
when its compartment is operating in heat
mode as long as at least one other zone is
operating in cool mode. This is a normally
open valve
.
Engine Controls
The engine controls are used to control the
operation of the diesel engine (or electric motor)
as required by the microprocessor. The
microprocessor determines these requirements by
considering the setpoint, the software, the setting
of programmable features and the information
supplied by the sensors.
• Coolant Temperature Sensor - This sensor
monitors the temperature of the coolant in the
diesel engine. It is located on the diesel engine
thermostat housing and is connected to the
microprocessor via the WTP and WTN wires.
• Coolant Level Sensor - This sensor monitors
the level of coolant in the radiator used by the
diesel engine. It is located on the radiator
expansion tank. If the coolant level falls below
the sensor for a specified period of time a low
coolant condition is assumed to exist. It is
connected to the microprocessor via the CLS
wire.
• Oil Pressure Switch - The oil pressure switch
monitors the oil pressure of the diesel engine.
It is located on the engine side of the unit
frame. It is connected to the microprocessor
via the 20B and CHO- wires.
• Oil Level Sensor - The oil level sensor
monitors the oil level in the diesel engine. It is
located above the oil pan on the door side of
the engine. It supplies information on the oil
level to the microprocessor via the OLS wire.
The switch is closed with low oil level.
• Flywheel Sensor - This sensor monitors the
RPM of the diesel engine. The flywheel
sensor is located just under the door side
engine mount. It supplies engine speed
information to the microprocessor via the
RPMP and RPMN wires.
• Glow Plugs - The glow plugs are energized by
the microprocessor via the H wire to preheat
the engine.
• Starter - The starter is located on the
compressor side of the engine. It is energized
by the microprocessor via the 8S wire to crank
the engine.
• Fuel Solenoid -The fuel solenoid is located at
the rear of the injector pump and is used to
start and stop the flow of fuel to the diesel
engine. It is energized to start fuel flow by the
microprocessor via the 8D wire. The fuel
solenoid features two coils, a pull-in coil and a
hold coil. The pull-in coil draws
approximately 40 amperes and the hold coil
draws approximately 1 ampere. The pull-in
coil is momentarily energized by the fuel
solenoid timer for a few seconds to shift the
fuel linkage.
• Throttle Solenoid - The high speed (throttle)
solenoid is located just below the fuel
injection pump. It is energized by the
microprocessor via the 7D wire to initiate high
speed operation.
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