Defrost function When I try and defrost my front windscreen on my Audi A4 there is nothing from the blowers on the front windscreen. Any suggestions.

Most heater units default to defrost mode for safety reasons. If you have a vacuum activated system you have lost vacuum some place causing unit to default to defrost. Check engine compartment vacuum lines and bottle reservoir for leaks.

The problem you have comes from wiper blades causing friction in light rain conditions and can be cured by cleaning the rubber that contacts your windscreen with a rubber cleaner/conditioner or you can use spray silicone on the blades.

bad servo for the defroster remove glove box and check the linkages

check the vaccuum routing on your selector for leak listen for small hissing sound at selector check vaccuum diaphram under hood for leag plastic line goes into firewall

you need a new windscreen

I would look take off the front bumper wrap and see if there is a leak somewhere in the plumbing to the headlight washers, etc. I had this problem.

ONE OF THE HEATER DISTRIBUTION FLAP MOTORS FAULTY.UNSCREW GLOVEBOX AND YOU WILL SEE THE ONE THANS NOT WORKING(TURN ON BLOWERS TO TEST)

EASY FIX HAD SAME PROBLEM WITH MY AUDI A4 2002 JUST LAST WEEK.....WILL BE ONE OF THE CONTROL MOTORS FOR AIR FLOW...UNSCREW THE 4 OR 5 SCREWS THAT HOLD THE GLOVEBOX IN PLACE TAKE CARE TO UNPLUG GLOVEBOX LIGHT WHEN LIFTING OUT...NOW YOU WILL SEE ALL THE CONTROL MOTORS RIGHT-HAND SIDE OF YOU...EACH ONE CHANGES THE AIR FLOW ...THE ONE FOR THE WINDSCREEN IS THE ONE NEAREST TO THE FRONT OF THE CAR..UNPLUG THE WIRING CONNECTOR UNDO THE 2 SCREWS NOTING HOW THE MOTOR SHAFT ENGAGES...EASY....IF YOUR UNSURE WHICH CONTROL MOTOR IT IS TURN ON YOUR BLOWERS AND TEST EACH ONE..SIDE VENTS, DEMISTER,ETC...TRY AND GET A SECONDHAND CONTROL MOTOR FROM SCRAP YARD...DEALERSHIP PRICES JUST A JOKE.. FOR A CHEAP TINY MOTOR NOT MUCH BIGGER THAN A MATCH BOX OVER A £100 SCRAP YARD £5 POUNDS...........HOPE THIS WILL BE OF SOME HELP TO YOU...

ONE OF THE HEATER DISTRIBUTION FLAP MOTORS DEFECTIVE. UNSCREW GLOVEBOX AND YOU WILL SEE THE MOTORS.TEST WITH THE BLOWERS ON ,TRY EACH VENT TO FIND FAULTY MOTOR...

UNDO THE SCREWS FOR THE GLOVEBOX LIFT OUT THE WAY AND ON YOUR RIGHT HANDSIDE YOU WILL SEE 3 AIR DISTRIBUTION FLAP MOTORS ,THE ONE FOR THE WINDSCREEN IS THE NEAREST TO THE BULKHEAD. YOU CAN TEST THE BLOWERS AND YOU WILL SEE THE MOTOR VENTS WORKING OR THE ONE NOT WORKING IN YOUR CASE ..