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Winding
Start (S---C)
Run (R ---C)
Winding
Start (S--- C)
Run (R --- C)
MAJOR COMPONENTS
2- - Stage Control
The 2- -stage control board controls the following functions:
- - Low- - and high- -stage compressor contactor operation
- - Outdoor fan motor operation
- - Low ambient cooling
- - Crankcase heater operation
- - Compressor external protection
- - Pressure switch monitoring
- - Time delays
- - On 187A models, start relay and capacitor
Field Connections
On 187A models with non- -communicating (non- -Evolution)
system, the 2- -stage control receives 24vac low- -voltage control
system inputs through the R, C, Y1, and Y2 connections located at
the bottom of the control board (see Fig. 6). The 187A can be
controlled using a standard 2- -stage thermostat or Evolution User
Interface.
All 180A models are part of a complete Evolution communicating
system and use only the ABCD connections on the circuit board.
The 180A must be controlled using an Evolution User Interface for
proper equipment staging and operation
2- - Stage Compressor
The 2- -stage compressor contains motor windings that provide
2- -pole (3500 RPM) operation. Refer to Table 5 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 500 - -
550 psi on 187A models and 550 - - 625 psi on 180A models. The
compressor is also protected by an internal overload attached to
motor windings.
Compressor Control Contactors
The contactor(s) have a 24 volt coil. The electronic control board
controls the operation of the appropriate contactors.
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. 7 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.)
Table 5 – 2 ---Stage Compressor
(Winding Resistance at 70_F ± 20_ / 21.11_C ± 11.11_C)
187A024
187A036
2.74
1.98
0.80
0.75
180A024
180A036
1.40
1.29
1.32
0.89
187A048
1.55
0.48
180A048
1.52
0.64
THERMISTOR CURVE
90
80
70
60
50
40
30
20
10
0
0
20
40
(-17.77)
(-6.67)
(4.44)
TEMPERATURE °F (°C)
Fig. 7 - - Resistance Values Versus Temperature
IMPORTANT: Outdoor air thermistor and coil thermistor are
factory mounted in the final locations. Check to insure thermistors
are mounted properly per Fig. 8 and Fig. 9.
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:
S If the outdoor air sensor indicates ≥ 10_F/5.56_C warmer than
the coil sensor (or) the outdoor air sensor indicates ≥
20_F/11.11_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.
11
187A060
0.74
0.36
180A060
0.60
0.49
60
80
100
120
(15.56)
(26.67)
(37.78)
(48.89)
A08054
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