Carrier 50FK - Manual (Page 18)

Demand Limit — The demand limit function provides
a means to limit the cooling capacity of the VAV unit using
an external discrete switch function. When enabled by the
closure of the external switch, the control will limit the avail-
able compressor staging capacity according to user set points
established at demand limit potentiometer(s).
The unit controls support two types of demand limit: single-
step and 2-step control.
SINGLE-STEP DEMAND LIMIT — This function will limit
the total compressor staging based on the ratio of the set point
potentiometer’s wiper arm position to the full scale resis-
tance of the potentiometer. The exact percentage of capacity
reduction differs depending on the number of capacity steps.
A field-supplied potentiometer and control switch are re-
quired for this function. See installation section for speci-
fication on potentiometer and field wiring.
TWO-STEP DEMAND LIMIT — Two-step demand limit is
provided with the installation of the accessory Demand Limit
Control Module kit plus installation of 2 field-supplied con-
trol switches (SPST-NO each). This accessory control pro-
vides for a first step reduction of 50% to 100% of the maxi-
mum compressor staging; the second step provides for reduction
between 0% and 49%. The exact percentage of capacity re-
duction differs depending on the number of capacity steps.
When demand limit is active, the LED display will show
22 code .
INSTALLATION
Single-Step Demand Limit — A 3-wire 5 to 20 K-ohm po-
tentiometer must be field-supplied and installed. A single-
pole normally open switch is also required (field-supplied
and -installed). Locate the potentiometer (designated P4) and
the switch in a suitable location (external from the unit or in
the unit control box).
SENSOR 1 SENSOR 2 SENSOR 3 SENSOR 4
RED
BLK
RED
BLK
RED
BLK
RED
BLK
TO ACCESSORY SPACE
TEMPERATURE RESET
CONTROL BOARD
RED
BLK
12
TB3
15
SIZES 034-048
12
TB4
15
SIZES 054-104
SPACE TEMPERATURE RESET — 4 SENSOR AVERAGING APPLICATION
RED
BLK
RED
BLK
RED BLK
SENSOR 1 SENSOR 2 SENSOR 3
RED
BLK
SENSOR 6 SENSOR 5
RED
BLK
SENSOR 4
RED BLK
RED
BLK
RED
BLK
SENSOR 8 SENSOR 7 SENSOR 9
TO ACCESSORY SPACE
TEMPERATURE RESET
CONTROL BOARD
RED
BLK
12
15
TB3
SIZES 034-048
12
15
TB4
SIZES 054-104
SPACE TEMPERATURE RESET — 9 SENSOR AVERAGING APPLICATION
Fig. 26 — Space Temperature Sensor Averaging
NOTE: Sensor part number is HH79NZ014.
18