Carrier 38AB - Pressure Differential

CONTROL POWER AT 38AD UNIT
CR — Control Relay
HD — Heating Device
IFC — Indoor Fan Contactor
IFR — Indoor Fan Relay
LLS — Liquid Line Solenoid
R — Heating Relay (field-supplied 24-volt sealed coil, 10VA
maximum rating)
SDR — Solenoid Dropping Relay
TB — Terminal Board
TC — Thermostat, Cooling
TH — Thermostat, Heating
-— Factory Wiring
_Field Wiring
^Jumper removed only when separate 24-volt power sources are
available for heating and cooling
fTo control heating device and provide automatic indoor fan
operation on heating
-> Fig. 12 — Control Circuit Wiring with 24-Volt
Accessories (38AD units only)
Preliminary Charge — Refer to Carrier Standard
Service Techniques Manual, Chapter 1, Section 1-8,
for charging methods and procedures mentioned
below.
Charge system with approximately 25 lb of R-22
(75 lb for 38AD044, 38AB054,064 and 084 units)
by the Liquid Charging Method and Charging by
Weight Procedure.
Energize the Branch Circuit, set space thermostat
above ambient. Close field disconnect switch and
turn on unit circuit breakers. Be sure compressor
crankcase heater(s) is operating. Allow crankcase
heater(s) to operate a minimum of 24 hours before
starting unit.
To Start Unit, set space thermostat below ambient,
to ensure circuit operation. On 38AD044 and
38AB084, push control circuit reset button(s).
After starting unit, there will be a delay of about
'15 seconds (12 seconds on 38AD044 and
38AB084) before first compressor starts.
Charging System
1. Block condenser coils to maintain 125 F con¬
densing temp at 280 psig, then add additional
charge to clear sight glass. (If long liquid lines
or vertical lifts greater than 25 ft are used, a
liquid line sight glass should be installed at
condensing unit and used for charging
purposes.)
2. After sight glass has cleared, additional charge
must be added per Table 8, to flood subcooler
circuits in condensers.
After Charging the System, allow unit to run for
about 20 minutes. Stop unit and check compressor
oil level. Add oil only if necessary to bring oil into
view in sight glass. If oil is added, run unit for
additional 10 minutes. Stop unit and check oil
level. If level is again low, add oil only after
determining that piping system is designed for
proper oil return and that the system is not leaking
oil. Check the operation of all safety controls.
Replace all service panels. Be sure that control
panel door is closed tightly.
Table 8 — Charging Data (R-22)
UNIT
REFRIG CHG (lb)
REFRIG
STORAGE
CAP. (lb) f
Sub-cooler
Coil*
38AD024
8
70
38AD028
8
77
38AD034
7
99
3 8 AD 044 15
161
38AB054
12
154
38AB064
10
198
38AB084
21
322
*For maximum system capacity without receiver
f At 120 F condensing temp with condenser 80% full of
liquid
NOTE
Values shown do not include charging requirements for
cooling coils and piping
SERVICE
Capacity Control is by either one or two suction
pressure actuated unloaders. Each controls two
cylinders. Unloaders are factory set (see Table 9)
but may be field adjusted. No. 1 unloader is on
cylinder bank on same side of compressor as
terminal box.
CONTROL SET POINT (cylinder load point) is
adjustable from 0 to 85 psig. To adjust, turn
control set point adjustment nut (Fig. 13) clock¬
wise to its bottom stop. In this position, set point
is 85 psig. Then, turn adjustment counterclockwise
to desired control set point. Every full turn
counterclockwise decreases set point by 7.5 psig.
PRESSURE DIFFERENTIAL (difference between
cylinder load and unload points) is adjustable from
6 to 22 psig. To adjust, turn pressure differential
adjustment screw (Fig. 13) 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.
772
8