HIS4

Yesterday I noticed a high pitched whine coming from the front of the engine bay right after I started the car and turned on the A/C. When I turn off the A/C the sound goes away but as soon as I turn it on again the sound comes back. Searching the archives it seems that this is a common problem with the aux fan getting stuck in a high speed mode either because of a bad relay or something obstructing the radiator fan from turning. I checked while the car was running and the raditor fan was turning so I don't think that's it. By process of elimination I'm assuming it's either a relay or some type of thermostat or sensor. Is there an easy fix to this problem? If it is just swaping a relay, where is the relay for this. Last time I remember looking under there, there were a couple of relays right next to the fuse block. How much does a new relay cost? TIA

dscottjr

I thought the fan always ran on high when the a/c was on. never checked into it though.

HIS4

I thought the fan was temperature controlled so it shouldn't be going on as soon as the A/C turns on. Shouldn't it only turn on after it senses a certain temperature has been reached?

Andy Hedin

That was my understanding as well.

ModifiedA4

<ul><li><a href="http://www.robsaudiworld.com/Audi_S4_engine_english.pdf">pages 11-13</a></li></ul>

dscottjr

no, afaik, it's always on when the a/cs on and also comes on when the temp is hot enough.

HIS4

According to pages 11-13, it looks like I may have a thermoswitch or pressure switch problem.