Specifications

FORM 150.72-NM1 (908)
155
JOHNSON CONTROLS
8
LOAD LIMITING
Load Limiting is a feature that prevents the unit from
loading beyond the desired value. 2 and 4 compressor
units can be load limited to 50%. This would allow only
1 compressor per system to run. 3 and 6 compressor units
can be load limited to 33% or 66%. The 66% limit would
allow up to 2 compressors per system to run, and the
33% limit would allow only 1 compressor per system
to run. Five-compressor units may be load limited to
40% (1 compressor per system runs) or 80% (up to 2
compressors per system) are permitted to run. No other
values of limiting are available.
There are two ways to load limit the unit. The rst is
through remote communication via an ISN. Load limit
stages are sent through YORK Talk on pages 9 and 10
of feature 54. Page 9 is stage 1 load limit and page 10
is stage 2 load limit.
A second stage of load limiting the unit is accomplished
by closing contacts connected to the Load Limit
(XTBC1 – terminals 13-21) and PWM inputs (XTBC1
– terminals 13-20). Stage 1 of load limiting involves
closing the Load Limit input. Stage 2 of load limiting
involves closing both the Load Limit and PWM inputs.
The rst stage of limiting is either 80%, 66% or 50%,
depending on the number of compressors on the unit.
The second stage of limiting is either 40% or 33% and
is only available on 3, 5 & 6 compressor units. Table
19 shows the load limiting permitted for the various
numbers of compressors.
   
-


COMPRESSOR RUN STATUS
Compressor run status is indicated by closure of contacts
at XTBC2 – terminals 25 to 26 for system 1 and XTBC2
– terminals 27 to 28 for system 2.
ALARM STATUS
System or unit shutdown is indicated by normally-open
alarm contacts opening whenever the unit shuts down on
a unit fault, locks out on a system fault, or experiences
a loss of power to the chiller electronics . System 1
alarm contacts are located at XTBC2 – terminals 29
to 30. System 2 alarm contacts are located at XTBC2
– terminals 31 to 32. The alarm contacts will close when
conditions allow the unit to operate, or the fault is reset
during a loss of power, the contacts will remain open
until power is reapplied and no fault conditions exist.
COMPRESSORS
IN UNIT
STAGE 1 STAGE 2
2 50% -
3 66% 33%
4 50% -
5 80% 40%
6 66% 33%
TABLE 19 – COMPRESSOR OPERATION –
LOAD LIMITING