A* D2 Aircon.

[Jonamat]

Hi All, Does anyone understand the Auto climate control fitted to the 96 A8 4.2. The local main stealer has failed to come up with an answer.

System is freshly gassed..no leaks. Any journey at a decent speed, A/C runs fine ( I have fitted an indicator light to the clutch feed so I can see what is going on) and the clutch would stay engaged for hours and system runs fine. As soon as I lift off slightly, clutch drops out, typically if slowing down for a slip road.

Starting from cold with A/C on "Low" clutch stays engaged until normal engine temp (around 90C) is reached...clutch drop out. So town driving means no Aircon.

The control head has inputs of road speed from the inst cluster and two inputs from the ECU which I know drops the A/C on kickdown. Both pressure switches are Ok, so is the staged fan system. Anyone experienced this or found a remedy ?

[SneakyMcC]

Our 96 3.7Ltr has been playing up for some time. We had a re-gas which worked for an afternoon. I mentioned to the wife that at speed last weekend that the a/c was working fine, as we slowed down, it stopped like yours....The answer I dont have :-/

Please let me know if you find anything. :-)

[SneakyMcC]

AC works parked up with +3000rpm dialled in...

[SneakyMcC]

I'm going to see a fella tomorrow that reckons the above symptoms are because a fan has failed that cools the compressed CFC's in the system. He says that the gas gets hot when compressed and the AC system is shutting down on safety settings. Thats why at speed and at startup on a cold engine theAC works...Does this sound like b*llox?

[SneakyMcC]

From audiworld

Is the aux electric radiator fan coming on at idle, when you turn on the AC.

On later model VW's and Audi's (don't know about a '96), if this fan is disabled (fan or fan control unit), the AC will not operate at hot idle...to help save the engine coolant from overheating.

This aux fan (if applicable) should come on immediately with AC turned on, even at freshly started cold idle. I know on 2000 and later VW and Audi (my cars) this is the case.

Climate control - AudiWorld Forums

[SneakyMcC]

Actually wanted to clarify my answer a bit. This fan malfunctioning DOES shut off the AC at hot idle to prevent overheating of the refrigerant,so his advice was correct. BUT it IS a dual purpose fan which also kicks in (regardless of AC) to aid in cooling engine coolant in extreme conditions...hot idle in hot weather. The decision is made, however, by the aux fan control unit which gets it signals from climate control and engine temperature sensors.

I had exactly the symptoms you decribed in one of my cars. I realized that the aux elec fan (side by side w/belt driven fan on radiator) was not running at all...it really should run (at least at low speed) ANYTIME the AC is on in any conditions. I ran 12v directly to the fan (bypassing the control unit)and it worked fine. The fault was with a failed control unit, which I replaced and problem was solved.

In my case, using a basic home OBD scanner (simple handheld unit), no codes showed for this malfunction...BUT, a full featured unit like dealers use may likely read a code(?). The easiest way to start, as I stated, is to check the electric fan at idle with AC turned on...it should be running, when all is normal.

Hope this helps.

This is almost exactly what the A/C fella said to me. He's coming around this evening to have a looksee...