Since I bought my A4 the AC almost always comes on when I hit the "AUTO" button on my climate control. I would manually turn it off sometimes, especially when I knew I didn't need it. Recently though something has changed. While I had everything apart to replace my clutch I found I had a bad AC tensioner pully. I ordered one but it took about a week to arive so in the meantime I left the AC belt off and kept the climate control on manual.

Since replacing the pully the AC almost never comes on automatically now. When I use the defrost button the AC always came on before, as it should... no matter what the tempature is. Now it doesn't, and I can't turn it on manually either. If it gets warm inside the car the AC will come on automatically. I only know this because the sun was shining one day last weekend and the temp inside the car reached almost 80*. But it's not even getting close to that now sincethe weather has changed so drastically. Hard to tell if it works normally when hot.

Questions: What is the normal operation of the AC in the auto mode? Is it possible that something needs reprogrammed since I had the battery disconnected for a few days while doing the clutch?

Sorry for the long post, just trying to be as detailed as possible. Car is a 1999 A4 1.8T Q

Thanks.

 

I have a 2000, so it's probably the same or very similar. I never put the climate control on auto - it's just one of those things i never tried to learn howto use. I just set the temperature (usually 68-71) and the fan speed manually and it works fine. I also have a problem with mine, that if i hit the button to open just the floor vents the button sticks, the whole panel locks up on auto and i can't adjust a thing - none of the buttons work then. So now i never use that button- lol. Just use the manual temperature and fan speed settings and you should have no problems. If you need to have the auto temperature working, i'd recommend going to a dealer when they are not busy and have a service tech or salesperson (that knows the car) give you a tutorial on the climate control panel. then you teach me.

 

Many vehicles (including my Ford van) run the A/C compressor even when the heat is on to dehumidify the air running across the windshield as part of the defogger.

 

Yep, I knew that... but that's where my problem is. My AC isn't coming on with the defroster anymore. It use to before I replaced the pully, but it doens't now. And I can't even turn it on manually unless it warm inside the car.Nothing else has changed except the pully replacement (and the fact that the battery was disconnected for 3 days)

Bogie, I think the climate controls changed drastically in 2000... you have a double-din radio don't you?