19
Connect the potentiometer end terminals to terminals 8
and 9 on control terminal block TB3 (sizes 034-048) or TB4
(sizes 054-104) (see Fig 27). Connect the switch terminals to
the potentiometer wiper arm terminal and to terminal 10 on
TB3 or TB4.
To enable demand limit function, change DIP switch 5 to
position ON. (Disconnect control power before changing DIP
switch positions. Reconnect power after all changes have been
made.)
Set the potentiometer P4 to desired capacity reduction value.
Two-Step Demand Limit — Install the demand limit control
module (DLCM) according to the installation instructions pro-
vided with the accessory. Disconnect existing leads at connec-
tor J3 on the processor board (see instructions) and connect the
plug from the DLCM harness to connector J3.
Connect the field input control power wires (from the exter-
nal control relays) at the terminal strips marked IN1, RTN1,
IN2 and RTN2 (see Fig. 28 and 29).
To enable demand limit function, change DIP switch 5 to
position ON. (Disconnect control power before hanging DIP
switch positions. Reconnect power after all changes have been
made.)
Set the potentiometers DLCM-P1 and DLCM-P2 to desired
capacity reduction values.
Check the operation of demand limit function by using the
Quick Test procedures.
CONFIGURATION
Single-Step Demand Limit — Field-installed potentiometer
P4 establishes capacity reduction value for demand limit opera-
tion. Set this potentiometer between 0% and 100%. The exact
percentage of capacity reduction differs depending on the num-
ber of capacity steps.
Two-Step Demand Limit — Potentiometer P1 and P2 (locat-
ed on the accessory demand limit control module) establish the
capacity reduction values for each step of demand limit. Set po-
tentiometer DLCM-P1 between 50% and 100%. Set potenti-
ometer DLCM-P2 between 0% and 49%. The exact percentage
of capacity reduction differs depending on the number of ca-
pacity steps.
OPERATING SEQUENCE
Single-Step Demand Limit — If the field control switch to
the wiper arm terminal is open, all capacity stag es will be avail-
able (no demand limit in effect). When the field control switch
is closed, the compressor cooling capacity is reduced by the
amount set on potentiometer P4.
When demand limit is in effect, the LED display will show
code 22 . If a potentiometer setting or input is out of range, the
control will terminate the demand limit function and show
code 84 at the display LED.
Two-Step Demand Limit — If the field control switches are
both open (no power supplied to the Demand Limit Control
Module), all capacity stages will be available (no demand limit
in effect). When control power is supplied to terminal IN1 only
(field switch SW1 closes), the first step of the demand limit is
energized and the compressor cooling capacity is reduced by
the amount set on potentiometer DLCM-P1. When control
power is supplied to terminal IN2 (field switch SW2 closes),
the second step of the demand limit is energized and compres-
sor cooling capacity is reduced by the amount set on potenti-
ometer DLCM-P2.
When demand limit is in effect, the LED display will show
code 22 . If a potentiometer setting or input is out of range, the
control will terminate the demand limit function and show
code 84 at the display LED.
Control From Remote Building Management
System (BMS) — The unit control system is not a com-
municating control system, and it cannot be accessed directly
by a DDC (Direct Digital Control) control system (or by a
BACnet communication system). However, it is possible to
control some functions of these units via 4 to 20 mA or 2 to
10 vdc signals and discrete inputs (relay contact closures).
Functions that can be managed from or accessed from an
external control system include:
• Occupied/Unoccupied Status
• Night Setback Control
• Unit Supply Air Set Point Adjustment
• Demand Limit (1-stage or 2-stage)
• Supply Duct Pressure Set Point Adjustment
• External Alarm Signal
Remote control of the economizer cycle on these units is not
recommended. Refer to the Operating Sequence sect ion on
page 35 for a discussion on the economizer cycle operation.
034-048: TB3
054-104: TB4
8
9
10
5-20K
POTENTIOMETER
(P4)
SWITCH
Fig. 27 — Single-Step Demand Limit
Fig. 28 — Two-Step Demand Limit Module
NOTES:
1. Demand limit switches are field supplied and wired.
2. Demand limit control module terminal blocks will accept up to
12-gage wire.
3. is field wiring.
Fig. 29 — 115-Volt Field Wiring to Accessory
2-Step Demand Limit Control Module