Carrier 38AK024-044 - Oil Pressure Safety Switch (OPS); Compressor Protection; High-Pressure Switch; Low-Pressure Switch

Oil Pressure Safety Switch (OPS) in the control
circuit stops the compressor, and unit, if proper oil pressure
differential is not established at start-up or maintained
during operation. If OPS stops the unit, determine the cause
and correct before restarting unit. Failure to do so will
constitute abuse. Equipment failure due to abuse may void the
Warranty.
Compressor Protection
CIRCUIT BREAKER — Calibrated trip manual reset,
ambient compensated, magnetic breaker protects against
motor overload and locked rotor conditions.
DISCHARGE THERMOSTAT — A sensor in the dis-
charge gas of 06E compressor reacts to excessively high
discharge gas temperature and shuts off the compressor.
TIME GUARDS control protects compressor against short
cycling. See Sequence of Operation (page 16).
CRANKCASE HEATER minimizes absorption of liquid
refrigerant by oil in crankcase during brief or extended
shutdown periods. Control circuit is maintained if com-
pressor fan motor circuit breakers are turned off. Main
disconnect must be on to energize crankcase heater.
IMPORTANT: Never open any switch or disconnect
that de-energizes the crankcase heater unless unit is
being serviced or is to be shut down for a prolonged
period. After a prolonged shutdown on a service job,
energize the crankcase heater for 24 hours before
starting the compressor.
High-Pressure Switch has fixed, nonadjustable set-
tings. Switch is mounted on the compressor.
TO CHECK — Open the condenser fan circuit breaker.
Head pressure builds up until compressor shuts down. This
should be at the cutout pressure in Table 4. Close condenser
fan circuit breaker. After pressure drops to cut-in setting,
reset control circuit by opening, then closing the control
circuit switch. After control circuit is reset, the Time Guard
timer cycles and in approximately 5.5 minutes the com-
pressor restarts.
19
Low-Pressure Switch has fixed, nonadjustable settings.
Switch is mounted on the compressor.
TO CHECK — Slowly close liquid shutoff valve and allow
compressor to pump down. Do not allow compressor to
pump down below 2 psig (13.8 kPa). Compressor should £ :
shut down when suction pressure drops to cutout pressure in % ,
Table 4, and should restart when pressure builds up to cut-In
pressure shown.
Table 4 — Pressure Switch Settings, psig (kPa)
HIGH PRESSURE
Cutout | Cutin |
426 + 7 320 + 20
(2206 + 138)
Winter Start Control — Switch D in the 4-function
(2937 + 48)
timer bypasses low-pressure switch for 21^ minutes on unit
start-up.
LOW PRESSURE
27 +3
(186 + 21)
44 + 5
(303 + 34)
Head Pressure Control reduces condensing capacity
under low ambient temperature conditions.
FAN CYCLING — These 38AK units have standard
provision for fully automatic intermediate-season head
pressure control through condenser fan cycling. Fan no. 2 is
cycled by a fan cycling pressure switch (FCPS) which
responds to variation in discharge pressure. The pressure
sensor is located in the liquid line of the refrigerant circuit.
Fan no. 3 cycling is controlled by outdoor air temperature
through an air temperature switch (ATS) (38AK044 units
only).
The ATS is located in the lower divider panel between the .
compressor compartment and condenser section. Through;
a hole in the panel, the sensing element is exposed to air
entering the no. 1 fan compartment. Fan no. 1 is non-
cycling. Table 5 shows the operating settings of the fan
cycling pressure switch and the air temperature switch.
Table 5 — Fan Cycling Controls
CONTROL BY SWITCH OPENS SWITCH CLOSES
70 X 3 (21 t 1.7
160 + 10 (1103 + 69)
Pressure,
psig (kPa)
260 + 15 (1793 + 103)
NOTE: See Fig. 6, 7, 8 for fan arrangement