Carrier 30H - Manual (Page 9)

HIGH-PRESSURE SWITCH (HPS)
The HPS settings are nonadjustable. Table 5
shows the factory settings for this switch.
If the HPS cuts out while the unit is in normal
operation (2-1/2 minutes or more after compressor
start-up), the compressor will stop and lock out. To
restart the compressor, the ON-OFF control circuit
switch must be manually pressed to OFF and then to
ON. The timer will start, and after approximately
5.5 minutes, the compressor will start under Time
Guard control. If the pressure has not dropped to
the HPS cut-in point (see Table 5), the compressor
will stop again immediately and again lock out. No
further attempts to restart should be made untd the
trouble is found and corrected. Unless the control
circuit switch is pressed to OFF at this time, the
timer will continue to run for approximately 1-1/2
minutes and then stop.
If the control circuit switch is left at ON, the
control circuit remains partially energized, includ­
ing the timer relay. Consequently, if the pressure
drops to the HPS cut-in point before restart, the
compressor
overtemperature protector (COP) light
will come on. This should not be cause for alarm in
this case since the light is functional only when the
discharge
temperature thermostat contacts open
during normal unit operation.
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RANGE ADJ SCREW
TURN CLOCKWISE TO RAISE BOTH CUT-IN
AND CUT0UT(7PSI PER TURN),
LPSl LPS2
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
Table 5 — Pressure Switch Specifications
UNIT зон
PRESSURE High Fixed
RANGE (psig) Low 10 to 90 Adjustable
DIFFERENTIAL High 103 ±19 (Fixed)
SETTING (psi) Low 13 to 50 Adjustable
FACTORY High
Cutout Cut-in
335 ±10 —
SETTING (psig) Low 29 ±4 1 44 ±4
TOW-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. Table 5 shows
the factory settings for this switch.
If the LPS cuts out while the unit is in normal
operation (any time after 2-1/2 minutes from com­
pressor start-up), the timer starts and runs for
approximately 5.5 minutes. The compressor then
starts, bypassing the LPS for 2-1/2 minutes under
Time Guard® control. If the LPS cut-in pressure is
reached
within the 2-1/2 minutes, the compressor
continues to run; if the required pressure has not
built up, the compressor stops at the end of the 2-1/2
minutes and locks out.
Further attempts to restart the unit must not be
made until the trouble has been found and cor­
rected.
The LPS contacts must be closed before the
compressor can be restarted after lockout.
Check Capacity Control System
DESCRIPTION
Capacity control is a system which loads and
unloads compressor cylinders and starts and stops
the compressors to maintain load requirements. The
system includes a 4-step temperature controller
and cylinder unloaders (see Table 2). Table 6 shows
the capacity control steps.
Table 6 — Capacity Control Steps
SEOUENCE1 SEQUENCE 2
UNIT CONTR
%
Cap.
Oper Cyl f Oper Cyl
ЗОН STEPS
Tot.
Ckt Í Ckt
1 1 2
Cap. j Tot.
Ckt i Ckt
1 1 2
1 25 2 2 i — 25 i 2 — i 2
040
2 50 4 2 ; 2 50 i 4 2 ! 2
3 75 6 4 : 2 75 6 2 1 4
4 100 8 4 ; 4 100 : 8 4 ; 4
1 40 4 4 : — 20 : 2 ^ ! 2
050
2 60 6 4 , 2 60 : 6 4 : 2
3 80 8 6 ; 2 80 ^ 8 4 i 4
4 100 10 6 i 4 100 10 6 i 4
1 33 4 4 : — 33 1 4 — i 4
060
2 67 8 4 : 4 67 М 8 4 4
3 83 10 6 М 4 83 1 10 4 : 6
4
100 12 6 1 6 100 ! 12 6 ) 6
4-STEP TEMPERATURE CONTROLLER
This controller consists of 4 load switches
actuated by pressures developed in a temperature­
sensing bulb located in the return water line of the
chilled water system. The controller is factory set to
control from
return water temperature thru a cool­
ing range of 10 F. The sequence switches are
factory calibrated and sealed and should not require
any field changes.
I MPtJR I .AN I: If a different return-water cool­
ing range or lea\'in^-\\.atcr control is specified,
or if brine below 10 F'i.s to be used, the controller
must be changed. Consult local Cai’rier rep­
resentative for proper control device.
The return water temperature at which the last
step of capacity unloads is indicated by the leaving
water temperature design setpoint on the adjustable
dial (Fig. 8).