Installation guide

Amber Status Light (STATUS)
An amber colored STATUS light is used to display the operation
mode and fault codes as specified in the troubleshooting section.
See Table 6 for codes and definitions.
NOTE: Only one code will be displayed on the outdoor unit control
board (the most recent, with the highest priority).
Utility Interface with Non-Communicating Thermostat
The utility curtailment relay should be wired in the Y2 thermostat
lead. This allows a power utility device to interrupt high stage
compressor operation during peak load periods. If the utility
requires control of low stage compressor operation a second
utility curtailment relay should be wired in the Y1 lead.
NOTE: Utility curtailment is not available when operating in
communicating mode. To apply utility curtailment with the Observer
Wall Control you must use a daughter board kit to convert the control
signals to standard thermostat signals.
Compressor Operation
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 75%
cooling 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.
Crankcase Heater Operation
The crankcase heater is de-energized when the compressor is
running. The crankcase heater is energized when the
compressor is off and the ambient is less than 42 ° F. When the
ambient temperature is between 65° F and 42 ° F the crankcase
heater is energized 30 minutes after the compressor is turned off.
When the ambient is above 65 ° F the crankcase heater remains
de-energized after the compressor is turned off.
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°F (37.8°C) to allow for easier starting during next
cooling cycle.
On *CA7 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 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 between the PWM1 and PWM2 terminals on the
circuit board with a volt meter set to DC volts.
Table 3 - Outdoor Fan Motor PWM
Outdoor Temp (DC volts, Tolerance +/- 2%)
Model Low-Stage High Stage Low & High Stage
Size OAT _ 104OF/40oc OAT_ 104OF/40oc OAT > 104OF/40oc
*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
Time Delays
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 hold the "Cool To" or "Heat To" button
on the Observer Wall Control for 10 seconds.
• 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 (Observer Communicating Wall
Control only).
• One minute time delay of outdoor fan at termination of
cooling mode when outdoor ambient is greater than or
equal to 100°F (37.8°C).
• There is no delay between staging from low to high and
from high to low capacity. The compressor will change from
low to high and from high to low capacity "on the fly" to meet
the demand.
TROUBLESHOOTING
If the compressor fails to operate with a cooling call, Table 4 can
be used to verify if there is any damage to the compressor
windings causing system malfunction.
Table 4 - Winding Resistance
Winding Resistance At 70°F +/- 20°F
(21.11°C +/- 11.11°C)
Winding 24 36 48 60
Start
(S-C) 1.64 1.52 1.86 1.63
Run
(R-C) 1.30 0.88 0.52 0.39
Systems Communication Failure
If communication with the Observer Communicating Wall Control
will flash the appropriate fault code. (See Table 6) Check the
wiring to the wall control, indoor and outdoor units.
Model Plug
Each control board contains a model plug. The correct model
plug must be installed for or the system to operate properly (see
Table 5).
8 Specifications subject to change without notice. 421 01 1702 04