10
One Minute Stage Change Time Delay on 25HNA6 Models
When compressor changes stages from high to low or low to
high, there is a 1−minute time delay before compressor restarts.
The outdoor fan motor remains running.
Compressor Operation on 25HNA6 Models
When the compressor operates in high stage operation, the
compressor motor rotates clockwise. Both the lower and upper
pistons are eccentric with the rotating crankshaft and both
compress refrigerant.
When the compressor operates in low stage operation, the
compressor motor reverses direction (rotates counterclockwise).
The lower piston becomes idle and the upper piston compresses
refrigerant. The start and run windings are reversed.
Crankcase Heater Operation
The crankcase heater is energized during unit off cycle regardless
of outside air temperature (OAT) on 25HNA6 models.
The crankcase heater is energized during off cycle below 65F on
25HNA9 models.
Outdoor Fan Motor Operation
The outdoor unit control energizes outdoor fan anytime
compressor is operating, except for defrost or low−ambient
cooling. 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 100F. This
reduces pressure differential for easier starting on next cycle. On
25HNA6 models, the outdoor fan remains energized during the
1−minute compressor staging time delay.
On 25NHNA6 models, the outdoor fan motor is a PSC type. A
fan relay on the control board turns the fan off and on by opening
and closing a high voltage circuit to the motor. It does not change
speeds between low and high stage operation.
On 25HNA9 models, the outdoor fan is an ECM type. The motor
control is continuously powered with high voltage. The motor
speed is determined by electrical pulses provided by the PWM
outputs on the control board. The ECM motor RPM adjusts to
outdoor conditions as described in Table 3. The PWM output can
be measured with a volt meter set to DC volts.
In low ambient cooling (below 55ºF) on 25HNA6 models, the
control board cycles the fan off and on, and for 25HNA9 models,
the PWM output is adjusted by the control as described in Low
Ambient Cooling section.
Table 3—Outdoor Fan Motor PWM Above 55_F
Outdoor Temp (DC volts, Tolerance +/− 2%)
Model
Low Stage
(OAT≤104F)
High Stage
(OAT≤104F)
Low & High
Stage
(OAT>104F)
25HNA924 4.0 4.8 10.0
25HNA936 4.5 6.5 10.0
25HNA948 6.0 8.1 10.0
25HNA960 7.8 9.6 10.0
NOTE: For 25HNA9 models in low−ambient cooling, the PWM output for
both high− and low−stage equals the value for low−stage opera−
tion below 104F.
Time Delays
The unit time delays include:
Five minute time delay to start cooling or heating
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 re−cycle 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 100F.
Fifteen second delay at termination of defrost before
the auxiliary heat (W1) is de−energized.
Twenty second delay at termination of defrost before
the outdoor fan is energized.
Thirty second compressor delay when quiet shift
enabled.
On 25HNA6 models there is a 1 minute time delay
between staging from low to high and from high to low
capacity. On 25HNA9 models there is no delay; the
compressor will change from low to high and from
high to low capacity “on the fly” to meet the demand.
Compressor Operation on 25HNA9 Models:
The basic scroll design has been modified with the addition of an
internal unloading mechanism that opens a by−pass port in the
first compression pocket, effectively reducing the displacement of
the scroll. The opening and closing of the by−pass port is
controlled by an internal electrically operated solenoid. The
modulated scroll uses a single step of unloading to go from full
capacity to approximately 67% capacity.
A single speed, high efficiency motor continues to run while the
scroll modulates between the two capacity steps. Modulation is
achieved by venting a portion of the gas in the first suction
pocket back to the low side of the compressor, thereby reducing
the effective displacement of the compressor.
Full capacity is achieved by blocking these vents, thus increasing
the displacement to 100%. A DC solenoid in the compressor
controlled by a rectified 24 volt AC signal in the external
solenoid plug moves the slider ring that covers and uncovers
these vents.
The vent covers are arranged in such a manner that the
compressor operates at approximately 67% capacity when the
solenoid is not energized and 100% capacity when the solenoid is
energized. The loading and unloading of the two step scroll is
done ”on the fly” without shutting off the motor between steps.
NOTE: 67% compressor capacity translates to approximately
80% cooling or heating capacity at the indoor coil.
The compressor will always start unloaded and stay unloaded for
five seconds even when the thermostat is calling for high stage
capacity.
25HNA
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