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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.
Step 2—Sequence of Operation

The 48DU 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 1—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

350 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.

UNIT OPERATION HAZARD

Failure to follow this caution may result in unit damage.
For cooling operation, the recommended airflow is 350 to 450

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.

CAUTION

For gas heat operations, Table 4 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

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 65

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

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.

Table 4—

Air Delivery and Temperature Rise at Rated Heating Input

Unit

Rated Heating Input (Btu/hr)

Heating Rise Range (

Heating Rise (Either Stage,

High Stage

Low Stage

High Stage

Low Stage

“Efficiency”