With the recent heat wave we have had the expected influx of customers with air conditioning faults, it is usually a case of refilling or top up of refrigerant to rectify the problem but this case was different. This Citroen climate control had not functioned for around 18 months and after the customer spending over £250 on unnecessary repairs at another garage the fault still remained.
I started with a diagnostic interrogation of all modules that influence the ac, bsi, climate control, and pcm, numerous error codes were read so i began with a fault clear broadcast. After studying live data in various modules i established refrigerant pressure was ok and that the various control circuits were functional. However i could see from a live data channel in the pcm that despite request from climate control the compressor operation was being prohibited. I once again read the error codes in the pcm and discovered a reoccurrence of a code i had previously erased namely P0597. This code refers to thermostat heater control circuit, this vehicle is equipped with an electronically controlled thermostat (see photo) and i suspected this was the cause of the fault. A quick check of the sensor showed open circuit, the customer was informed and a new sensor was installed. The error code would now permanently erase and the ac functioned perfectly.