Load Limiting; Compressor Run Status; Alarm Status; Table 19 - Compressor Operation - Load Limiting - York YLAA0285SE Manual

FORM 150.72-NM3 (1020)
ISSUE DATE 10/05/2020

LOAD LIMITING

Load Limiting is a feature that prevents the unit
from loading beyond the desired value. Two and four
compressor units can be load limited to 50%. This would
allow only one compressor per system to run. Three and
six compressor units can be load limited to 33% or 66%.
The 66% limit would allow up to two compressors per
system to run, and the 33% limit would allow only one
compressor per system to run. Five-compressor units
may be load limited to 40% (one compressor per system
runs) or 80% (up to 2 compressors per system). No other
values of limiting are available.
There are two ways to load limit the unit. The first 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 first 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.
TABLE 19 – COMPRESSOR OPERATION –
LOAD LIMITING
COMPRESSORS STAGE 1
IN UNIT
2
3
4
5
6
JOHNSON CONTROLS
STAGE 2
50% -
66% 33%
50% -
80% 40%
66% 33%
Simultaneous operation of Remote
Load Limiting and EMS­PWM Tem-
perature Reset (described on following
pages) cannot occur.

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.
SECTION 8 – UNIT OPERATION
175
8