Design Set Point Adjustment; Cylinder Unloading System; Unit Operation.10-11; Control Power - Carrier 30HK Installation, Start-Up And Service Instructions Manual

UNIT OPERATION
The return water temperature at which the last
step of capacity unloads is indicated by the leaving
water temperature design set point on the adjustable
dial (Fig. 8).
Example:
Design set point is at 44 F. On a reduction in load,
the capacity of the unit will be reduced to zero when
return water temperature drops to 44 F, and unit
will cycle off.
DESIGN SEl POINT ADJUSTMENT
When unit is ready for operation, insert small
screwdriver in adjusting slot (Fig. 8) and rotate to
turn dial (dial may also be turned by hand). Rotate
until design set point for installation appears direct¬
ly under pointer. Insert a thermometer in the return
chilled water connection and allow unit to run thru a
cycle. At instant the last step of capacity unloads
(switch no. 1 opens), read temperature. If it is not
same as dial reading, variation can be compensated
by shifting control point slightly.
Control Power
(115 volts) can be from a separate
source, thru a 15-amp fused disconnect or can be
taken from the main unit power source, thru a
field-supplied transformer shown on wiring label.
Control Sequence
— At initial start-up, assume
all safety devices are satisfied and the chilled water
temperature controller switches are all in position
for maximum cooling capacity.
Close compressor circuit breaker and press con¬
trol circuit ON-OFF switch to ON. The timer starts
and, depending on position of timer the compressor
starts in approximately 12 seconds to 8 minutes. At
compressor start-up, D-Dl contacts (see Four-
Function Timer and Fig. 4) are closed, bypassing
low-pressure switch for 2-1 / 2 minutes. In addition,
the E-El contacts are closed, bypassing the oil safety
switch (if used) for approximately 35 seconds. Both
these bypass functions protect against compressor
continuing to run under conditions that could cause
damage to the compressor. Barring any malfunc¬
tion, when timer contacts A-A2 close, approxi¬
mately 2-1/2 minutes after start-up, unit is in normal
operation. The timer stops when A-A2 contacts
close and holds in this position while the tempera¬
ture controller regulates the cooling capacity by
loading and unloading compressor cylinders, and by
stopping and starting the compressor, under Time
Guard® control, in response to load requlrements.
Fig. 8 — Set Point Adjustment
CYLINDER UNLOADING SYSTEM
Each unloading device is the cylinder head suction
cutoff type, which unloads 2 cylinders (one bank)
when the control solenoid is energized. Load
switches in the temperature controller energize and
de-energize the cylinder unloaders.
Unit Stoppage and Restart
— After each descrip¬
tion of a possible cause for unit stoppage is a short
description of the normal method of restart.
1. CONTROL POWER INTERRUPTION (IN¬
CLUDES BLOWN FUSE).
After power is restored, or fuse replaced, restart
is automatic thru normal timer cycle.
2. CONTROL CIRCUIT ON-OFF SWITCH IS
OPENED.
The timer motor starts automatically, runs for
approximately 5-1/2 minutes, and then stops.
To restart, press ON-OFF switch to ON. Com¬
pressor will start in approximately 12 seconds.
3. CONTACTS OF ANY AUXILIARY INTER¬
LOCK ARE OPEN.
After trouble has been corrected, restart is
automatic thru the normal timer cycle.
4. LOW WATER TEMPERATURE CUTOUT
CONTACTS ARE OPEN.
Allow time for water temperature to rise 5 F;
then press the control circuit ON-OFF switch to
OFF, and back to ON. This restarts timer. Unit
restarts automatically on the normal timer cycle.
5. CONTROL CIRCUIT FUSE BLOWS.
Refer to Stoppage Cause No. I above for normal
restart description.