The Blower Assembly
The blower assembly consists of a plastic blower wheel that is connected to a PSC indoor blower motor. A set screw holds
the blower wheel to the blower motor.
The indoor blower motor is a Multi Speed Fan Motor that is connected to the indoor unit control board. The wiring from the
motor to indoor board consists of 4 wires connected to pins common, low , medium and high speeds.
During normal operation, the indoor control board will energize the indoor blower motor and request proper speed. The
motor has a run capacitor that is located in the Cassette unit's control box. The run capacitor connects to the motor via
two orange wires. This capacitor is field replaceable.
The louver motors are stepper type motors that move the louvers up/down. The motors are controlled by pulsed voltage
that cannot be measured. If the louver does not move when it should, check for a bind in the louvers.
Piping Temperature Sensor
The Piping Temperature Sensor senses indoor coil temperature in the cooling mode and in the heating mode. This sensor is
used for Anti Freezing and Anti Cold Blow cycles. The sensor also provides critical temperature information to the ECU that
may be used in frequency adjustments.
Ambient Temperature Sensor
The Ambient Temperature Sensor senses room temperature. This sensor provides room temperature information to the
ECU for calculation of inverter capacity and temperature control.
Both sensors are negative temperature coefficient type that reduce electrical resistance as temperature rises.
The indoor unit circuit board controls the switching functions of the indoor unit. All control decisions are made by the
outdoor unit ECU. The indoor board has some limited diagnostic capability which will be covered in this manual.
Condensate Pump & Float Switch
LARGE CASSETTE TECHNICAL OVERVIEW