Unit Description (Rev 1/99)
8
Oil Separator
An oil separator is a standard feature. It separates compres-
sor oil from refrigerant vapor and returns the oil to the com-
pressor through the oil fill hole by using a special adapter.
The oil separator helps provide positive oil return at high
compressor speeds and low operating temperatures. This
feature enhances compressor lubrication and extends com-
pressor life. Units built after November 1996 will be located
in the condenser section. Refer to photo on page 12 and
drawing on page 61.
UNIT OPERATION
These units shift between cool, null, and heat (optional) to
maintain the box temperature at the thermostat setpoint.
The operating modes are: cool, null, heat (optional), and
defrost.
Engine Operation
The thermostat controls the operation of the unit by energiz-
ing and de-energizing the power relay and the heat relay.
The thermostat places the unit in cool by energizing the
power relay. The thermostat places the unit in null by de-
energizing all the relays. The thermostat places the unit in
heat by energizing the heat relay.
When the power relay is energized, power flows to energize
the fan relay and the compressor clutch through normally
closed contacts in ER2.
When the heat relay is energized, it closes contacts that
energize the fan relay, the water pump, and the water valve.
When the fan relay is energized, it closes contacts that ener-
gize the condenser and evaporator fans. The condenser fan
is also controlled by the condenser fan pressure switch.
This normally open switch monitors the compressor dis-
charge pressure. When the discharge pressure rises to 180 ±
10 psi (1241 ± 69 kPa), the switch closes and energizes the
condenser fan. When the discharge pressure drops to 130 ±
10 psi (896 ± 69 kPa), the switch opens and de-energizes the
condenser fan.
Electric Standby Operation
During electric standby operation, the thermostat controls
the operation of the unit by energizing and de-energizing the
power relay, the electric relays, and the heat contactor. The
thermostat places the unit in cool by energizing the power
relay and the electric relays.
The thermostat places the unit in null by de-energizing all
the relays and contactors. The thermostat places the unit in
heat by energizing the heat contactor.
When the power relay and the electric relays are energized,
they close contacts that energize the fan relay, the motor
contactor, and the electric standby compressor clutch.
When the heat contactor is energized, it energizes the elec-
tric evaporator heaters and the fan relay.
Cool
The thermostat shifts the unit to cool at temperatures more
than 5.4 F (3 C) above the thermostat setpoint. The thermo-
stat keeps the unit running in cool until the temperature falls
to the thermostat setpoint.
During engine operation the engine compressor and the
evaporator fans operate while the unit is in cool. During
electric operation, the electric motor, the electric standby
compressor, and the evaporator fans operate while the unit
is in cool.
Null
The thermostat shifts the unit from cool to null at the ther-
mostat setpoint. The thermostat shifts the unit from null to
heat at 3 F (1.7 C) below the thermostat setpoint. The ther-
mostat shifts the unit from heat to null at 2.4 F (1.3 C) above
the thermostat setpoint. The thermostat shifts the unit from
null to cool at 5.4 F (3 C) above the thermostat setpoint.
To Next Page
Loading...
Need help?
General
