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FOR SERVICING ONLY — To speed up the 5-minute anti-
short cycle, a temporary jumper may be placed between ter-
minals T1 and T6 of the control module.
This jumper must be removed after servicing is com-
plete. Failure to remove this jumper is considered abu-
sive treatment and will void the Carrier warranty.
Bypass Relay (BPR) —
BPR located in the control section of the control box. See
Fig. 9A or 9B. The function of the BPR is to provide a 2-minute
bypass of the LPS at start-up, and to energize the unload-
er(s) at start-up to provide unloaded compressor starting. Two
minutes after the compressor starts, the BPR completes its
function and is no longer active in the control circuit until
the next restart of the unit.
Time-Delay Relay (TDR) (50 Hz Only) —
state delay-on-make relay is factory set for a 1-second delay.
The number 1 dip switch is set to the ON position, and all
the other dip switches are set to the OFF position. Once the
control relay (CR) is energized, the compressor contactor C1
is powered, and the first set of compressor windings is en-
ergized. After the 1-second time delay, contactor C1A is pow-
ered and the second set of compressor windings is energized
(part-wind start).
Sequence of Operation —
calls for cooling, the no. 1 condenser fan and compressor
start after CM initial time delay of 3 ( 2/–1) seconds. If an
optional airflow switch is used, compressor and no. 1 con-
denser fan will not start until sufficient indoor airflow has
closed the switch. After 3 seconds the compressor starts and
the liquid line solenoid valve for solenoid drop control opens.
The crankcase heater is deenergized. If the head pressure reaches
260 psig (1792 kPa) the second condenser fan starts. Fan
no. 3 (38AKS044 only) starts if outdoor ambient air rises
above 80 F (26.7 C).
If cooling demand is low, suction pressure at the com-
pressor drops. As the pressure drops, the compressor un-
loads 2 banks of cylinders as required. If cooling demand is
high and 2-stage operation is used, the second stage of the
thermostat activates the capacity control liquid line solenoid
which activates the second stage evaporator coil. The com-
pressor cylinders load or unload in response to compressor
suction pressure to meet evaporator load.
Two minutes after compressor starts, the BPR timer is deen-
ergized and the LPS bypass is deactivated. If the LPS trips
during the first 2 minutes of operation, the compressor will
remain operational. If the LPS trips after 2 minutes, the com-
pressor operation is interrupted, and the compressor cannot
restart until the 5-minute CM anti-short cycle timer expires.
As the space cooling load is satisfied, the second stage of
the thermostat opens, and closes the field-supplied capacity
control liquid line solenoid valve to deactivate the second
stage coil. The compressor adjusts the number of active cyl-
inders to meet the new load. When the space temperature is
satisfied, the first stage of the thermostat opens and the con-
trol relay and the BPR open. This closes the solenoid drop
control valve. The compressor stops and the crankcase heater
is energized, preventing refrigerant from migrating to the com-
pressor during the off cycle (solenoid drop refrigerant con-
trol). The CM anti-short cycling timer is energized and runs
for approximately 5 minutes. During this time, the compres-
sor is not able to restart.
All units are equipped with a
This solid-
When space thermostat
Complete Unit Stoppage
CAUSES — Interruption of supplied power, compressor over-
temperature protection, or open HPS causes compressor
stoppage.
RESTART — The unit recycles and restarts automatically
under the CM when power is restored. Stoppage by HPS, or
compressor circuit breaker requires manual resetting of the
control circuit. To restart the CM timer when HPS is tripped,
it is necessary to interrupt power to the unit, restarting the
CM logic. It is necessary to manually reset the compressor
circuit breaker at the unit.
If LPS is not closed within 2 minutes after compressor
starts, the compressor locks out and the outdoor fans con-
tinue to run. It stays locked out for 5 minutes until the CM
anti-short cycle timer expires. After 5 minutes, the LPS is
bypassed by the BPR (winter start control). It remains jum-
pered for 2 minutes. Because the LPS is jumpered, the com-
pressor restarts and runs for the 2-minute time period. At
the end of this 2 minutes, if the LPS has still not closed, the
compressor is again locked out. The outdoor fans continue
to run as long as there is a call for cooling. Automatic reset
of the LPS causes the CM to recycle so that the compressor
can start.
If sufficient compressor oil pressure has not been built within
2 minutes after the compressor starts, the unit is completely
deenergized until the oil pressure switch is manually reset at
the unit.
If unit or circuit stoppage occurs more than once due to
any safety device, the trouble should be corrected be-
fore any attempt to restart.
Turn off all power to unit before proceeding.
Access for Servicing (See Fig. 13)
COMPRESSOR SECTION — The compressor compart-
ment has 2 side access panels and one front door for ser-
vicing, providing access to compressor, all components of
the refrigerant system, electrical controls, and control box.
After opening front door there is an inner cover that must be
removed for access to control box (except 208/230-v and
460-v units).
OIL PRESSURE SAFETY SWITCH — Switch is manually
reset, and accessed by removing the side access panel on the
left side of the unit (as viewed from the compressor end).
See Fig. 13. The OPS is found in the compressor junction
box. Open the compressor circuit breaker prior to removing
the compressor junction box cover in order to access the OPS.
The liquid line service valve can be found behind the side
access door on the right side of the unit (as viewed from the
compressor end).
CONDENSER SECTION — Condenser fan motors and fans
can be serviced by removal of outlet grilles or side panels.
If a fan motor is serviced, be sure the wire fan guard is in
place over each fan before starting unit. See Fig. 14 for proper
fan adjustment. Tighten fan hub securely on motor shaft with
setscrew which bears against the key. Be sure to replace Per-
magum and rubber cap over end of motor shaft to protect
against moisture causing fan to rust on shaft.
17
SERVICE
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