What the sensor is for
An air conditioner temperature sensor gives the ECU a live reading from the A/C system, typically the evaporator. That's useful for A/C control, since the compressor can be cycled off before the evaporator ices up, and for logging when you're chasing a cooling complaint. Like most temperature sensors it's usually a two-wire thermistor: one signal wire to an analog voltage input (AVI) and one to signal ground.
Setting it up in NSP
- Wiring: assign the sensor to any free AVI. If it's a plain two-wire sensor, enable the pullup. Set the Input Type to match your calibration data: voltage or resistance. A K-type thermocouple is also supported.
- Calibration: on the main sensor node, load a calibration file with Load from File if you bought the sensor from Haltech, or enter the maker's data by hand. Use Save to File to keep a custom curve for next time.
- Display: set the minimum value. When the reading falls below it, number and gauge displays flash red.
- Diagnostics: enable the high and low voltage DTCs and give each a severity, which can trigger an engine protection level.
Voltage or resistance calibration?
Changing the Input Type changes what the calibration screen asks for. Choose resistance when all you have is a thermistor data sheet listing ohms against temperature, which is common for aftermarket and OEM sensors. Choose voltage when you already have a curve for the voltage the ECU will see. Either way, check the result: with the car sitting overnight, the reading should be close to ambient.
The display threshold here is a minimum. For an A/C sensor, a very low reading is the one that matters, because it points to a freezing evaporator or a wiring fault.
Troubleshooting
| Symptom | Usually |
|---|---|
| Reading pinned at one extreme | Open or shorted wiring, or the pullup off on a two-wire sensor |
| Reading plausible but offset | Wrong calibration, or voltage data entered with Input Type set to resistance |
Related sensors: A/C pressure and ambient air temperature.
