Check Unit Safety Devices.9; Safety Thermostat; High-Pressure Switch; Low-Pressure Switch - Carrier 30HK Installation, Start-Up And Service Instructions Manual

Check Unit Safety Devices
SAFETY THERMOSTAT (Fig. 6)
The low water temperature cutout (LWTC) pro¬
tects the unit against freeze-up due to operating mal¬
function. The sensing bulb is inserted into a well
located in the leaving water nozzle. As installed, the
standard control is factory set to open at 36 ± 2 F,
breaking the control circuit and locking out unit.
The contacts remake at 5 ± 2 F above cutout point,
but the control circuit switch must be pressed to
OFF and then to ON for unit restart. This action re¬
energizes the control circuit and starts the timer
under Time Guard® control.
The thermostat cuts out in a range down to -30 F,
but to obtain this range, the low-limit stop tab on the
underside of dial must be either cut or bent. Make
this adjustment only if necessary (when cooling
glycols or brines).
HIGH-PRESSURE SWITCH (HPS)
The HPS settings are nonadjustable. Table 6
shows factory settings for this switch.
If HPS cuts out while unit is in normal operation
(2-1/2 minutes or more after compressor start-up),
compressor will stop and lock out. To restart com¬
pressor, the ON-OFF control circuit switch must
be manually pressed to OFF and then to ON. The
timer will start, and after approximately 5-1/2 min¬
utes, the compressor will start under Time Guard
control. If the pressure has not dropped to the HPS
cut-in point (see Table 6), the compressor will stop
again immediately and again lock out. Do not
attempt to restart until trouble is found and
corrected. Unless control circuit switch is pressed to
OFF at this time, timer will continue to run.
Table 6 — Pressure Switch Specifications
UNIT 30
1
HK i HL
PRESSURE
RANGE (psig)
1
High
1
1 Low
1
Fixed * Fixed
10 to 90 Adjustable
DIFFERENTIAL
SETTING (psi)
High
1 Low
1 96 ± 17 (Fixed) | 1 03 ± 1 9 (Fixed)
i 13 to 50 Adjustable
Cutout
Cut-in 1 Cutout Cut-in
FACTORY
SETTING (psig)
1
High
1
Low
260 ±10
29 ± 4
— 335 ± 10
44 ± 41 29 ± 4 44 ± 4
LOW-PRESSURE SWITCH (EPS)
The EPS is bypassed for 2-1/2 minutes after
compressor start on all start-ups. The EPS has an
adjustable range from 10 to 90 psig and a differential
of 13 to 50 psi. See Fig. 7. Table 6 shows factory
settings for this switch.
If EPS cuts out while unit is in normal operation
(any time after 2-1/2 minutes from compressor
start-up) timer starts and runs for approximately
5-1/2 minutes. The compressor then starts, by¬
passing the EPS for 2-1/2 minutes under Time
Guard control. If the EPS cut-in pressure is reached
within 2-1/2 minutes, compressor continues to run;
if, on the other hand, the required pressure has not
built up, compressor stops at end of 2-1/2 minutes
and locks out.
Do not attempt to restart unit until trouble has
been found and corrected. The LPS contacts must
he closed bejore compressor can he restarted after
lockout.
/
RANGE ADJ SCREW
TURN CLOCKWISE TO RAISE
BOTH CUT-IN AND CUTOUT
(7 PSI PER TURN)
DIFFERENTIAL ADJ SCREW
TURN clockwise TO DECREASE
(8
PSi PER TURN). ONLY CUTOUT
CHANGES
(RIGHT SIDE OF CONTROL BOX, VIEWED FROM TOP)
Fig. 7 — Low-Pressure Switch (LPS)
Adjustment
Check Capacity Control System
DESCRIPTION
Capacity control is a system which loads and
unloads compressor cylinders and starts and stops
compressor to maintain load requirements. System
includes a 3-step temperature controller and cyl¬
inder unloaders (see Table 2). Table 7 shows ca¬
pacity control steps.
Table 7 — Capacity Control Steps
UNIT
30HK.
30HL
1
CONTROL
1
!
% 1
OPER
STEPS CAP.
1
CYL
L.... .
1
1
33
t .
2
015 I
2
67
4
3
_1
i
100
6
1
1
35
2*
020 I
2 so
2
I
3
1
100 4
025.
I
1
2
i
33
67
2
4
030
3
1
100 i
6
*Uses hot gas bypass.
3-STEP TEMPERATURE CONTROLLER
This controller consists of 3 load switches actu¬
ated by pressures developed in a temperature¬
sensing bulb located in return water line of chilled
water system. The controller is factory set to control
from return water temperature thru a cooling range
of 10 F. Sequence switches are factory calibrated
and sealed and should not require any field changes.
IMPORT AN I; H a different return-water cooE
mg lange or Iravmg-wuier control is specified,
or if brine below 10 F b to 1^ used, controlkr
must he changed. Consult local ('arrici repie-
senlatt\e tor proper control de\ice
10