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INSTALLATION INSTRUCTIONS
resistance is infinite, much lower than 32 ohms, or is
grounded, the compressor must be replaced.
MAJOR COMPONENTS
2-Stage Control
The 2−stage control board controls the following functions:
— Compressor high and low stage operation
— Outdoor fan motor operation
— Compressor external protection
— Pressure switch monitoring
— Time delays
Field Connections
On models with non−communicating (Thermostat other than
Observer Wall Control) system, the 2−stage control receives
24vac low−voltage control system inputs through the Y1, and
Y2 connections located at the bottom of the control board
(see Fig. 10). The OD units can be controlled using a
standard 2-stage thermostat or Observer Wall Control.
2-Stage Compressor
The 2−stage compressor contains motor windings that
provide 2−pole (3500 RPM) operation. Refer to Table 4 for
correct winding resistance.
Compressor Internal Relief
The compressor is protected by an internal pressure relief
(IPR) which relieves discharge gas into compressor shell
when differential between suction and discharge pressures
exceeds 550 − 625 psig The compressor is also protected by
an internal overload attached to motor windings.
Compressor Control Contactor
The contactor has a 24 volt coil. The electronic control board
controls the operation of the appropriate contactor.
421 01 1701 00
R−410A Split System Air Conditioner
TEMPERATURE THERMISTORS
Thermistors are electronic devices which sense temperature.
As the temperature increases, the resistance decreases.
Thermistors are used to sense outdoor ambient (OAT) and
coil temperature (OCT). Refer to Fig. 9 for resistance values
versus temperature. If the outdoor ambient or coil thermistor
should fail, the control will flash the appropriate fault code
(see Table 6.)
IMPORTANT:
Outdoor air thermistor and coil thermistor
are factory mounted in the final locations. Check to insure
thermistors are mounted properly per Fig.7 and Fig.8.
Thermistor Sensor Comparison
The control continuously monitors and compares the outdoor
air temperature sensor and outdoor coil temperature sensor
to ensure proper operating conditions. The comparison is:
— If the outdoor air sensor indicates 10_F (5.56_C) warmer
than the coil sensor (or) the outdoor air sensor indicates
20_F (11.1_C) cooler than the coil sensor, the sensors are
out of range.
— If the sensors are out of range, the control will flash the
appropriate fault code as shown in Table 6.
— The thermistor comparison is not performed during low
ambient cooling or defrost operation.
Failed Thermistor Default Operation
Factory defaults have been provided in the event of failure of
outdoor air thermistor and/or coil thermistor. If the OAT
sensor should fail, low ambient cooling will not be allowed
and the one minute outdoor fan−off delay will not occur. If the
OCT sensor should fail, low ambient cooling will not be
allowed.
OAT Thermistor must be locked in place with
spherical nib end facing towards the front of
the control box.
11
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