The air temperature sensor is used to compensate for changes in air density due to air temperature. Cold air has a higher density than warm air and therefore requires a greater volume of fuel to maintain the same air/fuel ratio. This effect is most noticeable in forced induction engines. The Haltech ECU will automatically compensate using the signal received from the air temperature sensor - once the air temperature correction map is setup and enabled in the programming software. The sensor should be mounted to provide the best representation of the actual temperature of the air entering the combustion chamber, i.e. after any turbo or supercharger and intercooler, and as close to the head as possible. The sensor needs to be in the moving air stream to give fast response times and reduce Heat-Soak effects. Be aware that in some situations, mounting the sensor into the inlet manifold (especially at the rear) may case Heat Soak problems. Once a suitable position has been located for the air temperature sensor, a hole should be drilled and tapped to accept the sensor. Remove the manifold or inlet tract from the engine before this is done so you don't get any metal particles entering the inlet manifold, as these will be drawn into the engine and may cause damage.
Note: The Haltech air temperature sensor will read temperatures up to 120° C and temperatures above this will be interpreted as a fault condition. The air temperature after some turbo and superchargers can exceed this. If this occurs with your engine you should consider fitting an intercooler to reduce air temperature and increase charge density.