Pressure Differential - Carrier 38AD Installation, Start-Up And Service Instructions Manual

CONTROL
SET POINT
ADJUSTMENT
NUT
PRESSURE
DIFFERENTIAL
ADJUSTMENT
SCREW
VALVE BODY
DIFFERENTIAL SCREW
SEALING CAP
(CAP MUST BE REPLACED
TO PREVENT REFRIGERANT LEAKAGE)
Fig. 8 — Compressor Capacity Control Unloader
PRESSURE DIFFERENTIAL (difference between
cylinder load and unload points) is adjustable from
6 to 22 psig. To adjust, turn pressure differential
adjustment screw (Fig. 8) counterclockwise to its
back stop position. In this position, differential is 6
psig. Then, turn adjustment clockwise to desired
pressure differential. Every full turn clockwise
increases differential by 1.5 psig.
Compressor Lockout Circuit — Units 38AD012
and 014 have a control to provide positive com¬
pressor lockout protection if an overcurrent or
overtemperature device trips out. The over current
protection devices (thermally actuated, automatic
reset overloads) are located in compressor terminal
box. Also, an overtemperature thermostat is im¬
bedded in compressor motor windings on "across-
the-line start" units. The "part-winding-start" units
have a thermostat externally mounted on compres¬
sor body.
TO RESTART COMPRESSOR - After determin¬
ing cause of compressor lockout and performing
required corrective action, push reset button on
control box door.
The lockout circuit will automatically reset
after shutdown due to power failure.
Time Guard Circuit for each compressor provides
for a 5-minute delay before restarting compressor
after shutdown for any reason. On start-up, the
Time Guard Timer causes a delay of 15 seconds
after thermostat closes, and fans start before
compressor will start. On 38AD012 and 014;460-
and 575-volt units outdoor air fan no. 2 starts up
with compressor. On compressor shutdown the
timer recycles for 4 minutes 45 seconds. During
this time the compressor cannot restart.
Head Pressure Control — A feeler bulb in the
condenser inlet airstream senses temperature of air
entering condenser to control no. 2 fan on
38AD012 and 014 and no. 2 and 3 on 38AD016.
Qpen and close temperatures of switch are shown
in Table 1.
Be sure that feeler bulb is not in direct contact
with coil surface. See INSTALLATION, Fan
Cycling Thermostat.
MOTORMASTER® SOLID STATE HEAD PRES¬
SURE CONTROLLER (32 Series accessory) may
be used on these units. Controller modulates rpm
of no. 1 condenser fan motor from zero to full
speed to provide condensing pressure control and
operation at lower ambient temperatures.
On 460-volt units, install a field-supplied trans¬
former and rewire condenser fan motor no. 1 for
230 volts.
On 575-volt units, install a field-supplied trans¬
former and replace 575-volt motor with 230-volt
motor (Carrier part no. HC44VL851 or
HC44VE851).
Crankcase Heater prevents refrigerant migration
and compressor oil dilution during shutdown
whenever compressor is not operating.
Both compressor service valves must be closed
whenever crankcase heater is de-energized for more
than six hours.
Fan Adjustment - Turn unit power off. Remove
fan guard and loosen hub setscrew. Adjust fan until
top surface of hub is 3/8 in. below top of venturi
rim as shown in Fig. 7. Then, tighten setscrew on
flat of motor shaft. Replace rubber hubcap. If
rubber hubcap is missing, seal fan hub recess with
permagum to prevent hub from rusting to motor
shaft.
Lubrication
FAN MOTORS have sealed lubricated bearings. No
provisions for lubrication are made.
COMPRESSOR has its own oil supply. Loss of oil
due to a leak in the system should be the only
reason for adding oil after the system has been in
operation.
Fig. 9 — Fan Adjustment
5