Carrier 50FC M20 Series - Page 48

48
Fig. 62 — Outdoor Air Temperature
Changeover Set Points
Outdoor Enthalpy Changeover
For enthalpy control, accessory enthalpy sensor
(P/N: HH57AC078) is required. Replace the standard outdoor
dry bulb temperature sensor with the accessory enthalpy sensor
in the same mounting location. See Fig. 65. When the outdoor
air enthalpy rises above the outdoor enthalpy changeover set
point, the outdoor-air damper moves to its minimum position.
The outdoor enthalpy changeover set point is set with the out-
door enthalpy set point potentiometer on the EconoMi$er IV
controller. The set points are A, B, C, and D. See Fig. 66 and 67.
The factory-installed 620-ohm jumper must be in place across
terminals S
R
and SR+ on the EconoMi$er IV controller.
Differential Enthalpy Control
For differential enthalpy control, the EconoMi$er IV controller
uses two enthalpy sensors (HH57AC078 and CRENT-
DIF004A00), one in the outside air and one in the return air duct.
The EconoMi$er IV controller compares the outdoor air enthalpy
to the return air enthalpy to determine EconoMi$er IV use. The
controller selects the lower enthalpy air (return or outdoor) for
cooling. For example, when the outdoor air has a lower enthalpy
than the return air, the EconoMi$er IV opens to bring in outdoor
air for free cooling.
Replace the standard outside air dry bulb temperature sensor with
the accessory enthalpy sensor in the same mounting location. See
Fig. 56 on page 44. Mount the return air enthalpy sensor in the re-
turn air duct. See Fig. 65. Wiring is provided in the EconoMi$er
IV wiring harness. See Fig. 63. The outdoor enthalpy changeover
set point is set with the outdoor enthalpy set point potentiometer
on the EconoMi$er IV controller. When using this mode of
changeover control, turn the enthalpy set point potentiometer fully
clockwise to the D setting. See Fig. 66 and 67.
Fig. 63 — Typical EconoMi$er
IV (W7212 Controller) Wiring
123
ON
OFF
123
ON
OFF
123
ON
OFF
123
ON
OFF
123
ON
OFF
123
ON
OFF
123
ON
OFF
123
ON
OFF
48°F
53°F
55°F
58°F
63°F
68°F
73°F
78°F
DIP Switch
Position
Changeover
Temperature
LEGEND
DCV — Demand Controlled Ventilation
IAQ — Indoor Air Quality
LA — Low Ambient Lockout Device
OAT — Outdoor-Air Temperature
POT — Potentiometer
RAT — Return-Air Temperature