Carrier 5H - Manual (Page 17)

b. Field Modifications - Install a 1/4 inch or
3/8 inch bypass line between the control oil
pressure connection' and the crankcase and
install a solenoid valve in this line.
Unloadable cylinders may be loaded or unloaded
by operation of this solenoid valve. When solenoid
valve is closed, full oil pressure is available to the
controlled cylinders and these will be loaded so
that compressor will be operating on 100%capac­
ity. When solenoid valve is open, oil pressure will
be bled from controlled cylinders and they will be
unloaded, so that compressor will then be opera­
ting at 50% capacity. A two-step thermostat con­
trolling compressor can thus utilize two capacity
steps by operating compressor starter and solen­
oid bypass valve.
2. Application Requiring More Than One Step of
Capacity Reduction - This can be furnished on
special order for compressors having 6,8, or
12 cylinders. Arrangement consists of furnish­
ing a Freon compressor with ammonia external
solenoid unloading type capacity control. Con­
trol can be furnished with or without three-way
valves (Table 11).
Table 11 - Capacity Control Steps and
Heat Pump Modification
SENSING PROPORTIONING TYPE
AVAILABLE
CAPACITY STEPS EXTERNAL 3-WAY
COMPRESSOR { % ) SOLENOID VALVES
5F40, 5H40, 46 100, 50 1
5F60, 5H60, 5H120 100, 66-2/3, 33-1/3 2
5H80 100, 62-1/2, 37-1/2 2
Motor Selection Data - Motor selection data based
on the brake horsepower occurring at the designed
operating condition is usually a satisfactory pro­
cedure for applications in the air conditioning suc­
tion temperature range. For selections at lower
design suction temperatures, it is necessary to
consider the pulldown operating condition, and this
consideration will frequently dictate the motor
size rather than the brake horsepower at the design
operating condition.
Fig. 13 - External Solenoid Type
Capacity Control
The required compressor starting torque is de­
pendent on the discharge pressure as well as the
pressure differential occurring during start-up
and is the same for any compressor speed. The
values shown in Table 12 indicate the maximum
starting torque for R-12, R-22, R-500 andR-502.
The starting torque for duplex units can be
determined by adding together the torque for
each compressor in the duplex arrangement. For
instance, the starting torque for a 5H40-60duplex
unit, operating with R-12 at a saturated discharge
of 100 F, would be 57 + 69 = 126 lb ft.
In the selection of a motor, it must be noted
that the required motor starting torque must
exceed the compressor starting torque only when
the compressor is operating at the same speed as
the motor. If the compressor speed is less than
the motor speed, as on some belt drive units, the
motor starting torque requirements are reduced
in proportion to the speed ratio between the com­
pressor and the motor because of the mechanical
advantage available to the motor.
Table 12 - Compressor Stirling Torques (At 1750 Rpm)
SATURATED DISCHARGE TEMPERATURE F
COMPRESSOR
SIZE
/0
UNLOADING
DURING
STARTING
80 F 100 F 120 F
R-12 R-500 R-22 R-502 R-12 R-500 R-22 R-502 R-12 R-500 R-22 R-502
Maximum Starting Torque - Ib-ft
5F20 None 19 23 30 32 27 32 42 45 34 40 53 57
5F30 None 22 26 34 37 30 35 47 50 39 46 61 65
5F40 75 18 21 28 30 25 30 39 42 32 38 50 53
5F60 66-2/3 22 26 34 37 30 35 47 50 39 46 61 65
5H40 75 42 49 65 70 57 67 89 95 74 87 115 123
5H46 75 55 64 85 91 74 87 116 124 96 113 150 160
5H60 66-2/3 51 60 79 85 69 81 107 115 90 106 140 149
5H80 75 58 68 90 96 79 93 123 130 102 120 158 169
5H120 66-2/3 91 107 141 151 123 144 191 204 160 189 249 266
S U P E R S E D E S
SECTION
5F,H-1X
PAGES 1-42
DATE 11-63
SECTION
PAGE
DATE 5F,H-1XA
17
10-66