Service Manual
55
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 75% 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.
Fan Motor
Fan motor rotates the fan blade that either draws or blows
air through outdoor coil to exchange heat between
refrigerant and air. Motors are totally enclosed to increase
reliability. This also eliminates need for rain shield.
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury or death.
Turn off all power to unit before servicing or replacing
fan motor. Be sure unit main power switch is turned off.
!
WARNING
The bearings are permanently lubricated; therefore, no oil
ports are provided.
For suspected electrical failures, check for loose or faulty
electrical connections, or defective fan- motor capacitor. Fan
motor is equipped with thermal overload device in motor
windings which may open under adverse operating
conditions. Allow time for motor to cool so device can reset.
Further checking of motor can be done with an ohmmeter.
Set scale on R X 1 position; check for continuity between
three leads. Replace motors that show an open circuit in
any of the windings. Place 1 lead of ohmmeter on each
motor lead. At same time, place other ohmmeter lead on
motor case (ground). Replace any motor that shows
resistance to ground, signs of arcing, burning, or
overheating.
Located above the compressor is a single- speed fan motor
and fan. The *CA9 and *CH9 air conditioner and heat pump
models use the ECM variable speed fan motor.
The outdoor Integral Control Motor (ECM), is a
variable- speed motor which operates from 450 to 850 rpm.
The motor is a dc permanent magnet- type motor with the
electronic controls integrated into its rear cover. The control
package includes a small diode bridge, capacitors, and
power switching devices. It converts ac to dc power and
switches the dc power to the motor windings on and off at
various rates to control the motor speed. The speed at
which the motor windings are thus commutated is
determined by a pulse width modulated (PWM) signal which
is received from the control board on the motor control lines.
The PWM signal is created by turning a DC signal on and
off once within a given period of time. The signal on time
relative to the signal total period defines the percent of the
PWM. For example, if the period is 5 sec and the control
power is turned on for 1 sec then off, the signal will remain
off for 4 sec before turning on again to start the next cycle.
The PWM is called a 20 percent duty cycle signal. If the on
time is increased to 4 sec of the 5 sec period, the PWM is
called an 80 percent duty cycle. The ECM reads the PWM
signal and increases the motor speed linearly from minimum
speed to maximum speed with the percent duty cycle value
of the supplied PWM signal.
Outdoor Fan Motor
Operation
There are two different types of motors used in the
Communicating 2- stage outdoor units. The *CH6 models
use a PSC type fan motor, and the speed does not change
between high and low speed operation.
On *CH9 models, an ECM fan motor is used to achieve
higher efficiency ratings of the system. 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. The 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/37.7°C. This reduces pressure differential for easier
starting on next cycle. On *CA7 and *CH6 models, the
outdoor fan remains energized during the 1- minute
compressor staging time delay.
On *CA7 and *CH6 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 *CA9 and *CH9 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 15. The PWM output can be measured with a volt
meter set to DC volts.
In low ambient cooling (below 55°F/12.7°C), the control
board cycles the fan off and on.
Table 15—Outdoor Fan Motor PWM
Outdoor Temp (DC volts, Tolerance +/ - 2%)
Model
Low Stage
(OAT104_F/40_C)
High Stage
(OAT104_F/40_C)
Low & High
Stage
(OAT104_F/40_C)
*CH924 8.72 9.35 11.90
*CH936 9.06 10.23 11.90
*CH948 9.91 11.04 11.90
*CH960 10.83 11.70 11.90
*CA924 9.57 10.88 11.90
*CA936 9.06 10.23 11.90
*CA948 9.91 11.04 11.90
*CA960 10.83 11.70 11.90
NOTE: For *CH9 models in low- ambient cooling, the PWM
output for both high- and low- stage equals the value for
low- stage operation below 55_F (12.8_C).