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versus outdoor temperature can be found in the unit Product Data
Sheet. The cooling load must be taken from structure’s heat
gain/loss calculations. The selected temperature is the point at
which high-speed capacity is needed and is just above the
low-speed balance point. (See Fig. 11.)

After temperature is selected, unit operates in high speed during
first-stage demand at any temperature at or above the setting.

ZONING SELECTION

If the STAGE 2 LATCH pot is set to the ZONE position,
compressor operating speed in either heat or cool mode is

determined by Y1 and/or Y2 inputs. The system operates in low
speed with a Y1 input and high speed with a Y2, or Y1 and Y2
input. This allows the multistage zoning system to determine what
heating speed is needed regardless of outdoor temperature or
switchover point.

DEFROST TIME SELECTION

The defrost interval can be field selected, dependent on local or
geographical requirements. It is factory set at 90 minutes but can
be changed to either 30 or 50 minutes by rotating DEFROST
TIME pot. (See Fig. 9.)

DEFROST

The 2-speed control logic for defrost function is the standard time
and temperature initiated, time or temperature terminated. Defrost
only occurs at outdoor temperatures less than 50°F. The control
initiates defrost when outdoor coil thermistor is 30°F (

2°) or less,

and selected defrost time (interval) has been accumulated during
unit operation. Termination occurs when coil thermistor reaches
80°F (

5°) or defrost period reaches a maximum of 10 minutes.

Defrost is always done in high speed, even if unit operation
requires low speed, unless zoning is selected. During defrost, unit
operates in high speed, energizes reversing valve O and auxiliary
heat W2, and de-energizes outdoor fan. Upon termination, there is
a 20-sec delay in outdoor fan being energized.

FIELD-INITIATED FORCED DEFROST

By placing a jumper across speed-up terminals for a minimum of
5 sec and then removing it, a defrost cycle can be initiated. (See
Fig. 9.) The cycle occurs only if outdoor ambient is less than 50°F,
regardless of outdoor coil temperature. The cycle terminates when
coil thermistor reaches 80°F (

5° ) or defrost period reaches a

maximum of 10 minutes.

FURNACE INTERFACE

This feature provides a heat pump lockout upon a demand for
auxiliary heat W2 and must be used when interfacing a heat pump
with a gas/oil furnace. Field selection of furnace interface FURN
INT option is done by connecting factory-supplied jumper to ON
position of terminal 3 connector. (See Fig. 9.)

NOTE:

Do not select the Furnace Interface Option if using a

Carrier Dual Fuel thermostat or the Thermidistat Control.

When this option is selected, heat pump is locked out of operation
any time there is a thermostat call for W2, or outdoor ambient is
below balance point pot setting. (See Fig. 9.) When unit requires
defrost, auxiliary heat W2 energizes the furnace. After defrost is
terminated, heat pump shuts down and furnace continues to
operate until thermostat is satisfied. To utilize this function, the
economic and/or thermal balance point must be determined. See
appropriate heat pump balance point worksheet in unit Product
Data Sheet.

Table 9—Factory Defaults

FAILED COMPONENT

FUNCTION

DEFAULT

Ambient Thermistor

Crankcase Heater

Energized during any off cycle

Second-Stage Latching

Does not function

Furnace Interface

Balance point does not function, but inter-
face still energizes furnace and locks out
heat pump with a call for W2

Heating Switchover Speed Point