Sensor sensibilities

Can a scan tool reduce the pressure of diagnosing air conditioning systems?

Published:  26 April, 2013

By Andy Crook

It is possible to observe operating pressures, temperature readings and the status of various actuators and strategies during system operation by simply observing the live data from the various sensors.

1. Cooling Fan Control Unit

2. Engine Control Unit

3. Body Control Unit (BSI)

4. Instrument Control Unit

5. Heating, Ventilation & Air Conditioning Control Unit (HVAC)

After switching the air conditioning on the temperature should drop rapidly. Below, the temperature is 2.5ºC after 30 seconds of air conditioning operation at an ambient temperature of 10ºC. The instrument panel module can provide switch information; this can be used to check the operation of the switch.

The engine control unit provides live data for the coolant temperature sensor, air conditioning request and authorisation status. This can be used to establish if there is a pressure or pressure switch fault causing the system to become inoperative. The compressor should cut in and out in a cycle, rapid cycling suggests a fault with the sensors or refrigerant level.

The functional tests available from the engine control unit are:

1. High speed fan assembly

2. Low speed fan assembly

The actual duty cycle can be seen in the live data as the fan unit reference speed.

Evaluating the data and performing functional tests can put the technician in a much better position to take the next diagnostic step, if they know how the system operates and what clues data has provided.

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