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WARNING
ELECTRIC SHOCK HAZARD
Turn off electric power before service or
installation. Extreme care must be used, if it
becomes necessary to work on equipment with
power applied.
Failure to do so could result in serious injury or
death.
user interface port of the elctronic control board . There should be 24VDC. (refer to Electronic Control Board
Identification, Fig 711)
4. If there is no voltage, replace the electronic control board (refer to Fig 712).
5. If 24 VDC is present replace the User Interface and/ or the ribbon cable.
Thermistors Description
The Wallmaster units have 4 sensors (Thermistors). Each thermistor is color coded and has a differnt function.
1. Indoor Coil (Yellow) - located on the evaporator coil next to the power board
2. Outdoor Coil (Blue) - located on the condensor coil.
3. Discharge Air (Black) - located on the front of the unit in the discharge air port.
4. Ambient Air (White) - located o nt he front of the unit in front of the air intake
Thermistor Testing
1. Gain access to Electronic Control Board (Refer to Control Board Replacement, Fig 712)
2. Locate thermistor plug and disconnect from Control Board. (refer to Control Board Identification, Fig 711)
3. Check for proper resistance. (refer to Thermistor Resistance values,Appendix.
4. If thermistor is out of tolerance, replace thermistor.
58
COMPONENTS TESTING
Testing the User Interface and Electronic
Control Board
If the User Interface does not turn on:
1. Make sure the unit has the proper voltage and that it is
turned on. Check power at Terminals L1 and L2. (refer to
Electronic Control Board Identification, Figure 711)
2. Disconnect the User Interface's wire harness on the
control board.
3. Using a voltmeter, check the outer pins on the
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Troubleshooting
