changoo

I recently bought a 98 A4 Quattro with the 2.8L. I am having a problem with the outside temperature sensor. When I first turn in on in the morning, it will display the correct temp and slowly drop down to -49. I normally wouldn't care, but that unit seems to also affect the interior temperature. I replaced the sensor itself thinking it was faulty, but have the same results. I tried to trace the wiring down the the A/C Control Module, but the junction box behind the driver kickplate is a rat nest of connections and hard to follow the lines. Any ideas on where the junction is, or how to pull the a/c module out? I could just make a jumper from the sensor the module directly to eliminate the wiring in between if I could pull the module out.
Not sure if this is related or not, but it sure takes a LONG time for the heater to warm up. It used to warm up quick, but has slowly died off. Any ideas?

5v/cyl

Outside temp sensor won't effect the heating, but it will make the A/C not work. No idea on sensor problem, but heater can be from heater core plugged up or a air bubble caught in it. Does the motor temp warm up normally? Thermostat would be suspect if not.

shellwig

Which outside temperature sensor did you replace? I believe there are two, one in front of the engine in the bumper and one behind the engine where the fresh air enters the cabin. I had the same problem on my A4 and it was the second one, it sticks into the fresh air duct under the pollen filter.

From what I understand the temperature reading displayed is the lower of the two sensors. When one shorts out it tends to give sub zero readings, which as 5v/cyl alluded too made August daytime driving unbearable. If you unplug the defective sensor the system will use the reading from the other, for the one under the bumper this is trivial, for the other one...

To reach it you seem to need long slender arms, from inside the cabin it is behind the glove compartment way up between the firewall and the blower motor. There is a spring clip on the sensor you need to pry off than pull the connector straight off. If unplugging it solves the problem hit up your local dealer for a replacement, I believe they run around $20 give or take a few bucks.
Once you unplugged to remove the sensor I found it easiest to go under the hood, remove the pollen filter and look down the duct, you will see a thin plastic rod sticking in about an inch or two. Grab near the base of it and turn it 90 degrees and push it into the cabin. It may get caught before it falls all the way to the floor. The newer ones are significantly shorter than the originals. Replacing it you need to PRESS and turn from the inside to lock it in place, if you try and pull it from inside the duct (the way you removed it) you could damage it.