Carrier 48TJD - Manual (Page 19)

19
CO
2
Control Set Up — If a CO
2
sensor is not being used,
proceed to the next section. If a CO
2
sensor is being used, per-
form the following:
1. Determine the value at which you want the minimum
position of the dampers to begin opening to allow a
greater amount of outdoor air to enter. The range is 800 to
1,400 ppm.
2. Locate the CO
2
SP (PPM) potentiometer and adjust to the
desired set point. See Fig. 38.
Mechanical Cooling Lockout — Determine the outdoor-air
temperature at which you want the mechanical cooling (com-
pressors) to be disabled. Locate the mechanical cooling lock-
out (MECH CLG LOCKOUT) potentiometer. To disable this
feature, turn the potentiometer counterclockwise (CCW) to the
OFF position. Otherwise, set the value between 10 and 60 F.
Mechanical cooling will not operate when the outdoor air tem-
perature is below this value. See Fig. 38.
Dry Bulb Changeover Set Up — Determine the dry bulb
changeover set point from Table 3. The settings are A, B, C
and D. Locate the ECON SP potentiometer and set the dry
bulb changeover set point. See Fig. 38. When the OAT is
above this set point, the damper is limited to minimum position
setting.
Table 3 — Changeover Set Points
*Field-installed accessory.
If a potentiometer fails, its setting will default to the values in
Table 4.
Table 4 — Default Potentiometer Settings
Ventilation Air (Minimum Position Set up) — If ventilation
air is not required, proceed to Step 5. If ventilation air is
required, perform the following:
1. The indoor fan must be on to set the ventilation air. Either
put the thermostat in the continuous fan mode or jumper
the R and G terminals at the rooftop unit connection
board.
2. Locate the minimum position (MIN POS) potentiometer.
Turn the potentiometer full CCW to fully close the out-
door air dampers. Turn the potentiometer gradually
clockwise (CW) to the desired position. See Fig. 38.
3. Replace the filter access panel. See Fig. 26. Ensure the fil-
ter access panel slides along the tracks and is securely
engaged.
4. Calculate the minimum airflow across the EconoMi$er.
a. Calculate % of outside air using the following
formula.
% Outdoor air through EconoMi$er
b. Divide total CFM by percentage outdoor air, this
gives outdoor air volume in CFM.
5. Turn on base unit power.
NOTE: The EconoMi$er begins operation three min-
utes after power up.
6. See Fig. 39 for barometric relief damper characteristics.
SETTINGS A B C D
Dry Bulb (°F) 73 69 66 63
Single Enthalpy* (Btu/lb) 27 25 24 22
Differential Temperature*
(°F, Not Adjustable)
2 2 2 2
Differential Enthalpy*
(Btu/lb, Not Adjustable)
1 1 1 1
POTENTIOMETER DEFAULT SETTING
CO
2
SP (PPM) 1,000
MECH CLG LOCKOUT 47°
ECON SP D
MIN POS (%) 20
% Outdoor air =
Mixture Temp – Return Air Temp
Outdoor Temp – Return Air Temp
Personal Injury Hazard. Avoid possible injury by keep-
ing fingers away from damper blades.
SUPPLY AIR
TEMPERATURE
SENSOR
MOUNTING
LOCATION
SUPPLY AIR
TEMPERATURE
SENSOR
Fig. 37 — Supply-Air Sensor Placement
Fig. 38 — EconoMi$er Control Adjustment
Potentiometers (Factory Settings)
0 200 400 600 800 1000 1200 1400 1600
FLOW (CUBIC FEET/MINUTE)
0.5
0.4
0.3
0.2
0.1
0
ST
A
TIC PRESSURE (IN. WG)
Fig. 39 — Barometric Relief Capacity