P3 - Reset Limit; P4 - Demand Limit; P6 - Warm-Up Set Point - Carrier 48DK024 Controls Operation And Troubleshooting

POTENTIOMETER
P1
P2*
P3
P4†
Minimum Economizer
P5*
P6
P7**
*Optional factory-installed economizer is required.
†Accessory two-step demand limit module is required (which has
2 potentiometers), or a 5 to 20 Kohm field-supplied potentiometer
is required for single-step demand limit.
**Accessory temperature reset is required.
NOTE: Potentiometers P1-P6 input data to pin terminal connector J3.
Potentiometer P7 inputs data to pin terminal connector J7.
In addition to the unit status switch inputs, the processor
board also accepts inputs from several potentiometers. See
Table 3. These potentiometers control various operational char-
acteristics of the system. Inputs are received by the proces-
sor through pin terminal connector J3. See Fig. 4.
All of the potentiometers must be set before the unit is
started in order for the unit to function properly. Each of the
potentiometers has a valid range that is used by the control.
The valid range is defined as the potentiometer's resistance
value that the control will not consider to be in error. This
is usually between 10% and 90% of the potentiometer's to-
tal resistance. The control has been programmed to accept
an operational range for the potentiometer, which may not
be the same as the valid range.
LEGEND
IN — Input
P — Potentiometer
RNT — Return
SW — Switch
Fig. 4 — Pin Terminal Connector J3 Potentiometer
Inputs
Table 3 — Potentiometer Inputs and Ranges
DESCRIPTION LOCATION
Leaving Air
Set Point
Economizer Economizer
Position
Accessory
Reset Limit
Demand Limit
Demand Limit
Accessory Board
Position
Warm-Up
Accessory Board
Set Point
Reset
Reset Board
Temperature
Factory Wiring
Field Wiring
Accessory
CONTROL
VALID
RANGE
Display
45 to 70 F
Board
0 to 100%
Motor
0 to 80 F
Board
0 to 100%
Board
0 to 100%
40 to 80 F
40 to 100 F
The potentiometer locations and functions are as follows:
P1 — LEAVING-AIR SET POINT — This potentiometer is
located on the display board. The VAV control uses a valid
control range of 45 to 70 F, and the potentiometer has a valid
range of −22 F to 70 F. If the set point is between 22 F and
45 F, the control will use a value of 45 F. If the set point is
outside of the valid range (less than −22 F or greater than
70 F), an alarm condition will be signaled and a default value
of 70 F will be used.
P2 — ECONOMIZER POSITION — Economizer feedback
potentiometer is located on the economizer motor. It has a
valid range of 0 to 100%, which is also the operational range
that the processor will accept. The microprocessor is pro-
grammed to indicate an alarm if the travel during initializa-
tion is less than 10% of the total potentiometer's resistance.
An alarm condition will also be signaled if the potentiom-
eter fails during operation, indicating that the damper blades
are stuck. If either situation occurs, the processor will try to
drive the economizer dampers closed.
P3 — RESET LIMIT — This potentiometer is located on
the accessory board (provided standard from the factory) in
the unit main control box and establishes the maximum amount
of reset that can be applied to the leaving-air set point (P1).
Reset is limited by the P1 default of 70 F. This potentiom-
eter is used only when accessory, field-installed temperature
reset is used. If temperature reset is used, DIP (dual, in-line
package) switch 2 must be in the ON position. This poten-
tiometer has a valid range of 0° F to 80 F. If the potenti-
ometer is outside this range, an alarm condition will be sig-
naled and reset will be terminated.
P4 — DEMAND LIMIT — The demand limit potentiom-
eter is used only if accessory, field-installed demand limit is
used, and if DIP switch 5 is in the ON position. The valid
range is 0% to 100%, which is also the operational range.
For single-step demand limit, a field-installed 5 to 20 Kohm
potentiometer must be used. Mount the field-installed po-
tentiometer in the unit main control box. Refer to accessory
demand limit control module installation instructions for ex-
act location.
The accessory two-step demand limit control is a
2-potentiometer system. If the potentiometer is out of the
valid range, an alarm condition will be signaled and demand
limit will be terminated.
4
DEFAULT VALUE
45 F if -22 F < P1 < 45 F
70 F if P1 > 70 F OR IF P1 < -22 F
None (0 if P2 is bad)
None
None
None
40 F if 0°F < P6 < 40 F OR IF P6 > 95 F
OR IF P6 < 0
80 F if 80 F < P6 < 95 F
None