Carrier 48TCA04---A12 User Manual

Page 71

Economizer
Economizer Exists
This point tells the controller if there is an economizer

installed on the unit.

Factory Default = NO if no economizer

YES if there is an economizer installed

Economizer Minimum Position
This defines the lowest economizer position when the

indoor fan is running and the building is occupied.

Factory Default = 20%

Range = 0--100 %

Economizer High OAT Lockout
If the outdoor air temperature rises above this value,

economizer cooling will be disabled and dampers will

return and stay at minimum position.

Factory Default = 75_F

Range = 55--80_F

Power Exhaust Setpt
When the economizer damper position opens above this

point the power exhaust operation will begin. When the

damper position falls 10% below the setpoint, the power

exhaust will shutdown.

Factory Default = 50%

Range = 20--90 %

NOTE: This point is only used when Continuous Occ
Exhaust = NO
Continuous Occ Exhaust
This point tells the controller when to run the power

exhaust if equipped on the unit. If set to YES, the power

exhaust will be on all the time when in occupied mode

and will be off when in unoccupied mode. If set to NO the

power exhaust will be controlled by the Power Exhaust

Setpoint.

Factory Default = NO

IAQ
Max Differential CO

Setpt

If the difference between indoor an outdoor air quality

becomes greater then this value the damper position will

stay at the IAQ Greatest Min Dmpr Pos. configuration

point

Factory Default = 650 PPM

Range = 300--950 PPM

IAQ Greatest Min Dmpr Pos.
This is the greatest minimum position the economizer will

open to while trying to control the indoor air quality, CO

differential.

Factory Default = 50% open

Range = 10--60% open

Clockset
This submenu screen allows you to set the date and time

manually. The Daylight Savings Time (DST) can also be

changed here. The date and time is automatically set when

ever software is downloaded. The clock is a 24 hour clock

and not am/pm. The time should be verified (and maybe

changed) according to unit location and time zone.

Factory Default = Eastern Standard Time

USERPW
This submenu screen allows you to change the user

password to a four number password of choice. The User

password change screen is only accessible with the

Administrator Password (1111). The ADMIN password

will always override the user password.

OPERATING SEQUENCES

Base Unit Controls
Cooling, Units Without Economizer

When thermostat calls for cooling, terminals G and Y1 are

energized.

The

indoor--fan

contactor

(IFC)

and

compressor contactor are energized and indoor--fan motor,

compressor, and outdoor fan starts. The outdoor fan motor

runs continuously while unit is cooling.

Heating, Units Without Economizer

When the thermostat calls for heating, terminal W1 is

energized. To prevent thermostat short--cycling, the unit is

locked into the Heating mode for at least 1 minute when

W1 is energized. The induced--draft motor is energized

and the burner ignition sequence begins. The indoor

(evaporator) fan motor (IFM) is energized 45 seconds

after a flame is ignited. On units equipped for two stages

of heat, when additional heat is needed, W2 is energized

and the high--fire solenoid on the main gas valve (MGV)

is energized. When the thermostat is satisfied and W1 is

deenergized, the IFM stops after a 45--second time off

delay.

Cooling, Unit With EconoMi$er IV

For Occupied mode operation of EconoMi$er IV, there

must be a 24--v signal at terminals TR and N (provided

through PL6--3 from the unit’s IFC coil). Removing the

signal at N places the EconoMi$er IV control in

Unoccupied mode.

During Occupied mode operation, indoor fan operation

will be accompanied by economizer dampers moving to

Minimum Position setpoint for ventilation. If indoor fan is

off, dampers will close. During Unoccupied mode

operation, dampers will remain closed unless a Cooling

(by free cooling) or DCV demand is received.

Integrated EconoMi$er IV operation on 48TC single

compressor model requires a 2--stage thermostat (Y1 and

Y2 switches).

When free cooling using outside air is not available, the

unit cooling sequence will be controlled directly by the

space thermostat as described above as Cooling, Without

Economizer. Outside air damper position will be closed or

Minimum Position as determined by occupancy mode and

fan signal.

When free cooling is available as determined by the

appropriate changeover command (dry bulb, outdoor

enthalpy, differential dry bulb or differential enthalpy), a

call for cooling (Y1 closes at the thermostat) will cause

the economizer control to modulate the dampers open and

closed to maintain the unit supply air temperature at 50 to

55_F. Compressor will not run.

48TC