Defrost not working - A4 Audi Cars & Trucks

out of reffrigirant ,or leaking vacuum switch so when you put on defrost it won't actually work

Vacuum diaphram that works the defrost has gotten a hole in it, or the vacuum hose going to it has come off. Find this diaphram and inspect it! Example of what it looks like is shown.

When you say defrost doesn't work, are meaning the blower or thermal defroster? If its the thermal defroster for the rear window this could be a fuse or the element has probably either stopped working or has come unglued from the window itself. This is a common problem. If its the blower for the front windshield defroster then it could very well be the actuator inside the dash that has malfunctioned and not opening when the selector is set at desired direction of circulation.

no the ac compressor doesn't have to work for the defrost to work. All car maker have to have a default to a safe condition.So that means if your ac fails the defrost will still work. I will take longer to defrost your window

Is your ac system working properly, its a important part of defrosting. Your ac is is turned on because it works as a dehumidifier when you defrost.

Sounds like a possible defrost system failure,there are multiple components in the defrost system that can trigger this symptom(defrost heater,defrost timer,thermostats) if the freezer cannot go through the defrost process the frost will build up on the evaporator restricting air flow, the freezer will seem to work, but early signs will be fresh food section will start to get warm. Good luck!

rear defrosters are an apllied film of semi metalic strips and if you get you windows tinted often the tint man accidentally nicks these strips cuasing the defroster to malfuction check for breaks in the srips

Take your vehicle to the garage who would inspect the car circuit.

it needs service,
i guess front glass defrost fails.
and 2 things must work , AC and the defrost damper
or #3 (overloads the function)
my heater core bad and leaking.(or its 2 hoses)