Carrier 38AH044 38AH044-134 Specifications download pdf (Page 50)

Pressure Relief — High-side pressure relief is provided

by a fusible plug in the liquid line at the service valve. For low-

side pressure relief, a fusible plug is inserted in the side of the

accumulator (all units except 38AH044-084 dual-circuit,

constant-volume units). See Fig. 50. The 38AH044-084 dual-

circuit, constant-volume units have a fusible plug in the suction

tubing. A pressure relief valve installed on the compressor re-

lieves at 450 psig (3102 kPa) (see Fig. 3-8).

CONTROL SET POINT — Control set point (cylinder load

point) is adjustable from 0 to 85 psig (0 to 586 kPa). To adjust

the set point, turn the control set point adjustment nut clock-

wise to bottom stop. (See Fig. 51.) In this position, load-up set

point is 85 psig (586 kPa). Turn adjustment counterclockwise

to desired control set point. Every full turn counterclockwise

decreases the load-up set point by 7.5 psig (52 kPa).

PRESSURE DIFFERENTIAL — Pressure differential (dif-

ference between cylinder load and unload points) is adjustable

from 6 to 22 psig (41 to 152 kPa). To adjust, turn pressure

differential adjustment screw counterclockwise to back stop

position. The differential pressure is now adjusted to 6 psig

(41 kPa). Turn the adjustment screw clockwise to adjust the

differential pressure. Every full clockwise turn increases the

differential by 1.5 psig (10 kPa).

Timer Functions — (See Timer Cycle, Fig. 52.) Each

refrigeration circuit is controlled by an independent timer

which allows for the independent operation of each refrigera-

tion circuit.

NOTE: The 38AH044-084 optional single-circuit units have

one timer which controls the lead compressor. Lag compressor

is controlled by CCPS (capacity control pressure switch).

SWITCH A — The timer is energized through contacts A-A1

or A-A2. This establishes the Time Guard function which pre-

vents compressor short-cycling. Start of compressor is delayed

approximately 5

minutes after shutdown.

SWITCH B — The compressor is initially energized through

contacts B-B1.

SWITCH D — Contacts D-D1 provide a 2

-minute bypass

of the low-pressure switch at start-up for winter-start control.

On 38AH044-084 optional single-circuit units, contacts D-D2

control start-up of compressor A2.

SWITCH E — Contacts E-E1 provide a 2-minute bypass of

the oil pressure switch at start-up. If oil pressure does not build

to the required minimum pressure in 2 minutes, the compressor

shuts down and the control circuit locks out.

On 38AH044-084 dual-circuit and 38AH094,104 units, lag

circuit B start-up is delayed 60 seconds after a call for cooling

is made to the circuit. This prevents compressor(s) in both lead

and lag circuits from starting at the same time.

BYPASS/SPEEDUP PINS — Bypass and speedup shorting

pins are provided for service troubleshooting purposes. Short-

ing the bypass pins will eliminate the 330-second short cycle

time delay. Shorting the speedup pins will decrease all timing

functions by a factor of 8. The bypass and speedup pin jumpers

must be removed after servicing.

Control Circuit Reset — The control circuit locks out

if the unit shuts down because of low oil pressure or excessive

high-side pressure. To reset the control circuit, open and close

the fan circuit breaker (FCB). This resets the timer, and the unit

restarts under Time Guard control. At start-up, if the low-

pressure switch (LPS) does not close after 2

minutes, the unit

shuts down. When the pressure builds enough for the LPS to

cut in, the control circuit is energized automatically and start-

up proceeds under Time Guard control.

38AH044-084 DUAL-CIRCUIT UNITS; 38AH094,104 —

If circuit A operation is insufficient for the cooling require-

ments, the thermostat second stage TC2 closes to bring

circuit B on-line for cooling. This circuit follows the same

sequence of operation as the lead circuit, except a 60-second

time delay relay (TDR) delays compressor start-up for 60 sec-

onds after the call for cooling.

CONDENSER

COIL

FUSIBLE

PLUG

SUCTION

LINE

DISCHARGE

LINE

COMPRESSOR RAIL

ACCUMULATOR

Fig. 50 — Accumulator and Fusible Plug

Fig. 51 — Pressure-Actuated

Capacity Control Valve

NOTE: Black denotes closed contacts.

Fig. 52 — Timer Cycle

a38-190tf

1 ... 49 50 51 52 53 54 55 56

Comments to this Manuals

No comments

Carrier 38AH044 38AH044-134 Specifications Page 50

Comments to this Manuals

Related products and manuals for Air compressors Carrier 38AH044 38AH044-134