Substitute Value Operation

SUBSTITUTE VALUE OPERATION

If an input potentiometer or sensor (or its circuit) fails, the control panel/module will ignore the faulty input and, in its place, use a replacement value which has been programmed into its memory for just this purpose. The replacement value, typically a mid-scale value for a particular input, allows the system to operate as normally as possible, despite the fault.

Substitute values for IHKA E38 components are:
- Desired temperature value (left or right) 75°F (24°C)
- Interior temperature sensor 68°F (20°C)
- Face-vent temperature sensor (left or right) 75°F (24°C)
- Heater core temperature sensor (left or right) 130°F (55°C)
- Evaporator temperature sensor 32°F (0°C)*
- Ambient temperature sensor 32°F (0°C)**

* The substitute value for the evaporator temperature sensor is below the A/C compressor cycling point (1-3°C). Therefore, if the evaporator temperature sensor signal is not plausible, the substitute value will switch the A/C system off.

** The IHKA control panel/module obtains ambient temperature information over the K-Bus, not from a dedicated IHKA system sensor. If the value received is not plausible (not between -40°C and +80°C), the control panel/module will ignore the supplied value and use the substitute value instead.