Sequence Of Operation - Carrier 30HS Series Installation, Start-Up And Service Instructions Manual

THROTTUNG (MODULATING) RANGE
ADJUSTMENT SCREW
SET POINT
ADJUSTMENT SCREW
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4
Fig. 7 — Chilled Water Temperature Controller
THROTTLING (MODULATING) RANGE SETTING, F
MINA BC DE F
90
80
70
60
30
20
10 20 30 40
I5 0
THROTTLING
RANGE
SCALE
SET POINT
(MAIN)
SCALE
temperature controller and motor balancing poten-
tiometer located at end of camshaft. When unit is
loading or unloading, (respectively, clockwise or
counterclockwise rotation as viewed from poten-
tiometer
end), each chilled water temperature
corresponds to a position of camshaft. A limit
switch restricts rotation in each direction.
At
initial start-up or after a power interruption,
a relay in the step controller ensures that the cam-
shaft will rotate in the unload direction to the
correct position to begin the compressor starting
sequence. After completion of the reset cycle, the
camshaft rotation reverses and the compressor
starting sequence begins.
Compressors start one at a time at 1:nief intervals
until load demand is satisfied. After completing '
starting sequence, controller will stop and start,
unload and load compressors to maintain
unit cooling capacity to satisfy load requirements.
Factory cam settings on step controller protect
compressors against rapid cycling.
Chilled Water Temperature Controller (Fig. 7)
— A sensing bulb is factory inserted in return water
nozzle of the chilled water system to relay water
temperature to potentiometer which actuates step
controller. Cams in step controller are factory-set
to control
from return water temperature.
If unit is
to be applied with control bulb in leaving chilled
water line, cams must be reset in field. If this is
required, contact local Minneapolis-Honeywell
representative.
Adjust set point (main scale) and throttling
(modulating) range
of
chilled water temperature
controller before initial start-up.
Set point = design leaving chilled water tem-
perature minus X value. The X values, established
by test, are such that the compressor is prevented
from cycling more than once in a 5-minute period.
See Table 6.
Throttling Range = Design Rise + X value. Enter
graph, Fig. 8 at set point and move across to inter-
section of throttling range. Read setting from top
scale (minimum to F).
Example: 30HR100 w/4 compressors, 10 F rise
45 F Leaving Chilled Water Temperature
Set Point:
45 — 1 = 44 F
Throttling Range: 10 + 1 = 11 F
Table 6 — "X" Values
NO. OF
COMPRESSORS
DESIGN RISE
8F 10 F 12 F
3
4
1.25
0.75
1.5
1.0
1.75
1.25
SEQUENCE OF OPERATION
The 115-1-60 control power can be supplied
directly from a separate source thru a code-
approved fused disconnect or thru a field-installed
accessory transformer with primary side con-
nected to the LI and L2 terminals of unit power
terminal block. A double-pole circuit breaker pro-
THROTTLING (MODULATING) RANGE, F
Fig. 8 — Temperature Controller Graph
tects control circuit and serves as control circuit
switch. Crankcase heaters are wiled in control
circuit ahead of the START-STOP switch. They are
always operative as long as control circuit switch is
on even though unit may be
off
because of safety
device action. Heaters are wired so they are on only
when their respective compressors are cycled off.
After a prolonged shutdown, the crankcase
heaters should be on for 24 hours before starting
the unit.
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