My problem is that the Turbo works fine until I turn on the Aircon, then it disappears. Have had the car to the garage on numerous times and they have changed various items, such as sensors but the problem persists. Without having to go to great expense I would like some idea what the problem could be? Does anybody have any ideas? Thanks

Hi I presume you are getting a massive power loss when aircon is on
are you sure turbo is working without air con because if its not the power loss would be quite dramatic
see if you can remove pipe to turbo and see if it spins free hope this helps

Yes there is no power loss with the airco switched off, yes it spins freely and the problem still persists but thanks for your help

Hi again it would be usefull to know the year and engine code
and what sensors have been replaced, Sensors don't have to be replaced they can be tested
Start by looking at these I am presumming the engine is in reasonable condition and not overheating or burning oil
Air filter restriction Air intake blockage or leakage
Fuel filter and pump have been checked
Access to data trouble codes would be usefull next step
Mass Air Flow Sensor if fitted also Turbo boost sensor again if fitted
Turbo wastegate regulator valve if fitted
Manifold absolute pressure sensor if fitted
egr exhaust gas valve soleniod or mechanical which ever
fuel quantity adjuster position sensor
fuel injection timing solenoid
fuel injection pump timing
brake pedal positioning switch
engine coolant temp sensor
air intake manfold control solenoid if fitted
and last the fuel temp sensor
that should cover every thing
The ECM trouble codes will also include air con Codes

hi ya mate . the problem could be a wiring fault or a sensor that you havent found yet. your best bet is to try and find a tech who works at a VAG dealership(v.w,seat,skoda,audi). thay can plug the computer system called 5051 and diag nose it properly, if you go round to the garage . u mite find some one who can do it on the side.