When the vent is set to face and you plant the foot, the air is re directed to the screen (under load) and returns back to the face when the accelerator is backed off. I have been told its possibly a one way valve problem????????????????????But where is it?

behind the w/screen washer bottle in the engine bay.

Thanks for the info, replaced the valve but the problem is still there anyone else with a remedy??????????

SOUND LIKE LOOSING VACUME YOU NEED A VACUME PUMP TO DIAGNOSE WHERE FROM IF YOU HAVE AN OLD FRIDGE THE COMPRESSORS WORK REALLY WELL BUT SOME TIMES YOU NEED A LOMG HOSE SO THAT THE PUMP/COMPRESSOR CAN BE FURTHER AWAY FROM THE CAR THEN YOU ATTATCH THE VACUME TO THE CAR AT THE ONE WAY VALVE AND GET INSIDE THE CAR YOU SHOULD BE ABLE TO HEAR A VACUME LEAK IT IS A BIT HARD TO DIAGNOSE THOUGH WITHOUT A VAC PUMP YOU MUST USE VACUME THOUGH AS A COMPRESSOR WILL JUST BLOW ALL THE HOSES OFF AND MAKE MORE PROBLEMS HOW LONG HAVE YOU HAD THE PROBLEM DID IT START AFTER FITTING A DIFFERENT STEREO SOME OF THE CONNECTORS CAN BE KNOCKED OFF QUITE EASILY HAS THE CAR HAD AN ACCIDENT THERE IS A VACUME STORAGE TANK THAT CAN GET DAMAGED HOPE SOME OF THIS HELPS
PS THE BIT ABOUT THE COMPRESSOR IS NOT MEANT TO BE A SMART a*** I HAD A CAR BROUGHT IN TO ME WITH THE HOSES BLOWN OFF