Quantech QCC2015CEE, Installation, Operation And Maintenance Manual, Page: 139 / 172

QUANTECH
139
SECTION 8 – UNIT OPERATION
Form QCC2-NM1
Issue Date: 5/20/2021
8
Load limiting
Load Limiting is a feature that prevents the unit from
loading beyond the desired value. Two and four com-
pressor 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 compres-
sors per system to run, and the 33% limit would allow
only one compressor per system to run. Five compres-
sor units may be load limited to 40% (one compressor
per system runs) or 80% (up to two compressors per
system) are permitted to run. No other values of limit-
ing are available.
There are two ways to load limit the unit. The first is
through remote communication via an ISN. A second
way to load limit the unit is through 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 in-
put. 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 limit-
ing is either 40% or 33% and is only available on 3, 5
and 6 compressor units.
Table 22 on page 139
shows
the load limiting permitted for the various numbers of
compressors.
Simultaneous operation of Remote Load
Limiting and EMS-PWM Temperature
Reset (described on following pages)
cannot occur.
Compressor run status
Compressor run status is indicated by closure of con-
tacts at XTBC2 – terminals 25 to 26 for system 1 and
XTBC2 – terminals 27 to 28 for system 2. The respec-
tive contact will close anytime a compressor is running
in that particular system.
The compressor Run Status contacts can also be used
to cycle the evaporator fan contactor with the compres-
sors.
Alarm status
System or unit shutdown is indicated by normally-
open contacts opening whenever the unit shuts down
on a unit fault, or locks out on a system fault. 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.
Table 22 - Compressor Operation – Load Limiting
COMPRESSORS
IN UNIT
STAGE 1 STAGE 2
2 50% -
3 66% 33%
4 50% -
5 80% 40%
6 66% 33%