Carrier 48TC Nomenclature Explained: Economizer Features and Operations

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 CO2 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, CO2 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

71