Carrier INFINITIR 15 SEER 48XT-A Installation Instructions Manual Download

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Sequence of Operation

The 48XT--A Hybrid Heat 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 heat pump 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 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 User Interface. 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.
HYBRID HEAT SEQUENCE OF OPERATION
The Hybrid Heat sequence of operation, from satisfied to full
heating, is as follows:
The system will attempt to satisfy the call for heat with the first

stage heat pump. There is a ten--minute staging timer before
switching to the second stage heat pump.

Second stage heat pump will run until call for heat is satisfied or
for fifteen minutes. If after 15 minutes the call for heat still exists,

the unit will stage to first stage gas.
For first stage gas the heat pump will be off unless the unit is in

defrost. There is a ten--minute staging timer on first stage gas. If

call for heat still exists after 10 minutes, the system will stage to
second stage gas and run until the call for heat is satisfied.

NOTE

: Heat stages are not shortened due to a 5 degree or higher

demand. All stages are utilized for the full allotted time described
above. If the UI determines it is making sufficient progress toward
set point, it may not stage up after the staging timer has elapsed.
Pressing

the

FAN

and

TEMPERATURE

buttons

simultaneously defeats cycle timers. See UI installation instructions
for more detail.
HEAT PUMP SEQUENCE OF OPERATION
COOLING AND HEATING OPERATION
With a call for first stage cooling, the outdoor fan, reversing valve,

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. The reversing valve will
remain energized until the control board power is removed or a call

for heating in initiated. With a call for heating, the outdoor fan and

compressor are energized. The compressor will operate in high or
low stage operation, as needed to meet the heating demand. When

the heating demand is satisfied, the compressor and fan will shut
off. The reversing valve is de--energized in the heating mode.

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. 14, 15 and 17). 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”.

Table 3 – Air Delivery and Temperature Rise at Rated Heating Input

Unit

Rated Heating Input (Btu/hr)

Heating Rise Range

F (

Heating Rise Either Stage,

F (

High Stage

Low Stage