Chapter 5: Troubleshooting
Switches/Thermostat
Service Manual 5-13
5.3.1 Humidifier Heater/Safety Thermostat
The humidifier has two separate heater elements rated at 225 watts at 104 volts. They are connected in
parallel for 115 volt operation and in series for 230 volt operation. The humidifier safety thermostat is in
series with the heater. It opens at 130 +/-5 C and closes at 90 +/-8 C. Measure the resistance at J53.1 to
J53.3.
The resistance of each heater is about 144 ohms so it should measure about 72 ohms for 115 devices, 288
ohms for 230 devices.
5.3.2 Compartment Air Probe and Skin Temperature Probes
Use the Service screen to read the temperature of the compartment and skin temperature probes.
There are two thermistors in each air probe or skin temperature probe. During stable temperature
conditions the thermistors should read the same resistance within a few ohms.
See “Compartment and Skin Probe Characteristics” on page A-1 for complete temperature/resistance
tables.
5.3.3 Heat Sink Sensor Thermistor
Use the Service screen to read the resistance of the heat sink sensor.
Skin temperature probe #1 Control bd J4 pins 1-3, 2-3
Skin temperature probe #2 Control bd J2 pins 1-3, 2-3
Compartment Air probe Control bd J1 pins 1-2, 3-4
Temperature (°C) Resistance (Ohms)
20 12527
25 10000
30 8037
35 6500
Thermistor Control bd J3 pins 1-2
Temperature (°C) Resistance (Ohms)
20 25000
25 20000
30 16102
35 13048
40 10636
80 2506
90 1827
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