Carrier 48XL User Manual download pdf (Page 20)

If thermistor is shorted or open, replace it to return the system to

normal operation. If fault is in the wiring connections, correcting

the fault will clear the code and return the system to normal

operation,

NOTE: If fault condition is an open thermistor or a wiring problem

that appears to be an open thermistor and the power to the unit is

cycled off, the fault code will be cleared on the next power-up but

the fault will remain and system operation will not be as expected.

This is because on power-up, the unit control cannot discern

the difference between an open sensor or if a sensor is not

installed.

Sequence of Operation

The 48XL packaged unit is designed for installation with a

communicating UI. This unit will not respond to commands

provided by a common thermostat except under certain emergency

situations described in Step f—Start-Up and Troubleshooting.

The UI uses temperature, humidity and other data supplied from

indoor and outdoor system components to control heating or

cooling system for optimum comfort. The unit will be commanded

by UI to supply airflow. The unit will operate the indoor blower at

requested airflow for most modes,

INDOOR AIRFLOW ADJUSTMENTS

The nominal requested airflow for air conditioner operations will

be 330 cfm per ton of nominal cooling capacity as defined by unit

size. Actual airflow request will be adjusted from nominal using

indoor and outdoor temperature and indoor humidity data to

optimize the system operation for occupant comfort and system

efficiency. Refer to UI literature for further system control details.

^ CAUTION

UNIT OPERATION HAZARD

Failure to follow this caution may result in unit damage.

For cooling operation, the recommended airflow is 330 to

430 cfm for each 12,000 Btuh of rated cooling capacity. For

heating operation, the airflow must produce a temperature

rise that falls within the range stamped on the unit rating

plate.

______________________________________________

For gas heat operations. Table 3 shows the temperature rise in each

gas heating mode. Refer to these tables to determine the desired

heating airflow for the system being installed.

NOTE: Be sure that all supply-and return-air grilles are open,

free from obstructions, and adjusted properly. Airflow can be

changed using the UI, See UI installation instructions for more

detail.

NOTE: Once the compressor has started and then has stopped, it

should not be started again until 4 minutes have elapsed. The

cooling cycle remains “on” until the room temperature drops to

point that is slightly below the cooling control setting of the UI,

AIR CONDITIONER SEQUENCE OF OPERATION

COOLING OPERATION

With a call for first stage cooling, the outdoor fan, and low stage

compressor are energized. If low-stage cannot satisfy cooling

demand, high-stage cooling is energized by the UI. After second

stage is satisfied, the unit returns to low-stage operation until first

stage is satisfied or until second stage is required again. When both

first stage and second stage cooling are satisfied, the compressor

will shut off.

NOTE: When two-stage unit is operating at low-stage, system

vapor (suction) pressure will be higher than a standard single-stage

system or high-stage operation,

NOTE: Outdoor fan motor will continue to operate for one

minute after compressor shuts off, when outdoor ambient is greater

than or equal to 100°F (38°C).

UTILITY INTERFACE WITH INFINITY CONTROL

The utility curtailment relay should be connected to factory

supplied pigtails (PINK, connected to R, VIOLET connected to Y2

on the control board) located in the low voltage splice box (See

Fig. 13, 14 and 16). This input allows a power utility device to

interrupt compressor operation during peak load periods. When the

utility sends a signal to shut the system down, the UI will display

“Curtailment Active”,

COMPRESSOR OPERATION

When the compressor is operating in low stage, the modulating

ring is deactivated, allowing two internal bypass ports to close off

33% of the scroll compression area so the system operates at part

load capacity. The 24-volt solenoid coil is de-energized in

low-stage operation.

When the compressor is operating at high stage, the modulating

ring is activated, sealing the bypass ports, which allows the

compressor to operate at full load capacity. The 24-volt solenoid

coil is energized in high stage operation,

CRANKCASE HEATER OPERATION (IF APPLICABLE)

The crankcase heater is energized during off cycle below 63 °F

(18°C) outdoor air temperature,

OUTDOOR FAN MOTOR OPERATION

The outdoor unit control energizes the outdoor fan any time the

compressor is operating. The outdoor fan remains energized if a

pressure switch or compressor overload should open. Outdoor fan

motor will continue to operate for one minute after the compressor

shuts off when the outdoor ambient is greater than or equal to

100°F (38°C).

TIME DELAYS-AIR CONDITIONER OPERATIONS

The unit time delays include:

• Five minute time delay to start cooling operation when there is a

call from the thermostat or user interface. To bypass this feature,

momentarily short and release Forced Defrost pins,

• Five minute compressor recycle delay on return from a

brown-out condition.

• Two minute time delay to return to standby operation from last

valid communication (with Infinity only).

• One minute time delay of outdoor fan at termination of cooling

mode when outdoor ambient is greater than or equal to 100°F

(38°C).

• There is no time delay between air conditioner staging from low

to high and from high to low capacity; the compressor will change

from low to high and from high to low capacity as demand

dictates.

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Carrier 48XL User Manual Page 20

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