52
RT-SVX25C-EN
Troubleshooting
Test 2
Cooling Set Point (CSP) and Heating Set Point (HSP) The resistance of these potentiometers are
measured between the following ZSM terminals. Refer to the chart above for approximate
resistances at the given setpoints.
Cool SP = Terminals 2 and 3
Range = 100 to 900 Ohms approximate
Heat SP = Terminals 2 and 5
Range = 100 to 900 Ohms approximate
Test 3
System Mode and Fan Selection
The combined resistance of the Mode selection switch and the Fan selection switch can be
measured between terminals 2 and 4 on the Zone Sensor. The possible switch combinations are
listed on the following page with their corresponding resistance values.
Test 4
LED Indicator Test, (SYS ON, HEAT, COOL & SERVICE)
Method 1
Testing the LED using a meter with diode test function. Test both forward and reverse bias. Forward
bias should measure a voltage drop of 1.5 to 2.5 volts, depending on your meter. Reverse bias will
show an Over Load, or open circuit indication if LED is functional.
Method 2
Testing the LED with an analog Ohmmeter. Connect Ohmmeter across LED in one direction, then
reverse the leads for the opposite direction. The LED should have at least 100 times more resistance
in reverse direction, as compared with the forward direction. If high resistance in both directions,
LED is open. If low in both directions, LED is shorted.
Method 3
To test LED’s with ZSM connected to unit, test voltages at LED terminals on ZSM. A measurement
of 32 VDC, across an unlit LED, means the LED has failed.
Table 11. Temps and resistance values
Zone Temperature
Nominal ZTEMP
Resistance
Nominal CSP
or HSP
Resistance
50 F°
10.0 C°
19.9 K-Ohms
889 Ohms
55 F°
12.8 C°
17.47 K-Ohms
812 Ohms
60 F°
15.6 C°
15.3 K-Ohms
695 Ohms
65 F°
18.3 C°
13.49 K-Ohms
597 Ohms
70 F°
21.1 C°
11.9 K-Ohms
500 Ohms
75 F°
23.9 C°
10.50 K-Ohms
403 Ohms
80 F°
26.7 C°
9.3 K-Ohms
305 Ohms
85 F°
29.4 C°
8.25 K-Ohms
208 Ohms
90 F °
32.2 C°
7.3 K-Ohms
110 Ohms
