Electrical Maintenance
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3. Raise the discharge pressure of the
compressor by blocking the condenser coil
airflow. Temporarily cover the compressor
compartment, control box and power cord
storage compartment with cardboard to reduce
condenser coil airflow. This should increase
the discharge pressure enough to cause the
switch to open. When the switch opens:
• The compressor and evaporator fans should
stop immediately.
NOTE: The discharge pressure should never
be allowed to exceed 2,760 kPa, 27.6 bar, 400
psig.
4. Be sure to remove the cardboard installed in
step 3.
If the HPCO switch fails to stop compressor
operation, replace the switch and repeat steps 1
through 4.
Low Pressure Cutout Switch
A low pressure cutout switch is located on the
compressor suction line. If the suction pressure
becomes too low, the switch opens to stop the
compressor:
• Compressor stops immediately.
• Evaporator and condenser fans continue
normal operation.
• Compressor will restart if the low refrigerant
condition is corrected (switch closes) as long
as power is available. The low pressure switch
resets (closes) when the pressure increases to
28 to 48 kPa, 0.28 to 0.48 bar, 4 to 7 psig (48
to 90 kPa, 0.48 to 0.90 bar, 7 to 13 psig before
1/2001).
Low Pressure Cutout Switch:
Opens: -17 to -37 kPa, -0.17 to -0.37 bar,
5 to 11 in. Hg vacuum (+21 to -21 kPa,
+0.21 to -0.21 bar, 3 psig to 6 in. Hg vacuum
before 1/2001)
Closes: 28 to 48 kPa, 0.28 to 0.48 bar, 4 to 7 psig
(48 to 90 kPa, 0.48 to 0.90 bar, 7 to 13 psig before
1/2001)
Condenser Fan and Evaporator
Fan Rotation
NOTE: If both the condenser fan and
evaporator fans are rotating backwards,
diagnose the automatic phase selection system.
Condenser Fan
Check for proper condenser fan rotation by
placing a small cloth or sheet of paper against the
condenser fan grille on the front of the unit.
Proper rotation will blow the cloth or paper away
from the grille. Improper rotation will hold the
cloth or paper against the grille.
If the condenser fan is rotating backwards, refer to
the unit wiring diagram to correct fan motor
wiring at the fan motor junction box or condenser
fan contactor. To correct improper fan rotation,
reverse any two fan power cord leads at the
condenser fan contactor (disconnect power supply
before reversing leads). Do not move the CH
ground wire.
Evaporator Fans
Visually inspect the evaporator fan blades for
proper rotation. Arrows located on the underside
of the fan deck indicate the correct direction of
rotation.
NOTE: Check both high and low speed
evaporator fan rotation by performing
Evaporator High and Evaporator Low tests from
the Manual Function Test menu of the
controller.
If an evaporator fans rotate backwards on one or
both speeds, refer to the unit wiring diagram to
correct motor wiring at the fan motor junction box
or evaporator fan contactor (disconnect power
supply before reversing leads). (Do not move the
ground wire which is labeled CH.)
NOTE: Evaporator fan motor wires EF1, EF2
and EF3 are used on low speed fan operation.
Wires EF11, EF12 and EF13 are used on high
speed fan operation.
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