Supply-Air Sensor Placement; Changeover Set Points; Default Potentiometer Settings; Barometric Relief Capacity - Carrier 48TJD Installation, Start-Up And Service Instructions Manual

SUPPLY AIR
TEMPERATURE
SENSOR
MOUNTING
LOCATION
SUPPLY AIR
TEMPERATURE
SENSOR
Fig. 37 — Supply-Air Sensor Placement
CO Control Set Up — If a CO
2
proceed to the next section. If a CO
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 SP (PPM) potentiometer and adjust to the
2
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
SETTINGS
Dry Bulb (°F)
Single Enthalpy* (Btu/lb)
Differential Temperature*
(°F, Not Adjustable)
Differential Enthalpy*
(Btu/lb, Not Adjustable)
*Field-installed accessory.
If a potentiometer fails, its setting will default to the values in
Table 4.
Table 4 — Default Potentiometer Settings
POTENTIOMETER
CO SP (PPM)
2
MECH CLG LOCKOUT
ECON SP
MIN POS (%)
sensor is not being used,
2
sensor is being used, per-
2
A B C D
73 69 66 63
27 25 24 22
2 2 2 2
1 1 1 1
DEFAULT SETTING
1,000
47°
D
20
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
% Outdoor air =
b. Divide total CFM by percentage outdoor air, this
gives outdoor air volume in CFM.
5. Turn on base unit power.
NOTE: The EconoMi$er begins operation three min-
utes after power up.
Personal Injury Hazard. Avoid possible injury by keep-
ing fingers away from damper blades.
6. See Fig. 39 for barometric relief damper characteristics.
Fig. 38 — EconoMi$er Control Adjustment
Potentiometers (Factory Settings)
0.5
0.4
0.3
0.2
0.1
0
0 200 400
Fig. 39 — Barometric Relief Capacity
19
Mixture Temp – Return Air Temp
Outdoor Temp – Return Air Temp
600 800 1000 1200 1400 1600
FLOW (CUBIC FEET/MINUTE)