Assistance needed please.

[Codinc]

Ok guys, I've run into quite the quagmire on my C5 S6. The A/C fan runs all of the time when the car is on regardless if the A/C is on or not. I've had a local indie shop look at my car, as well as a Master Audi Tech, and still the problem persists (my VAG-COM pulls no codes). I've replaced coolant temp sensor, temp switch, Fan control module, and now per instructions from a Master Tech I've even replaced the ECM/ECU. Still to no avail unfortunately. During a hot day in traffic, the car overheats if stagnant with the A/C on, so my next intuition is to replace A/C fan, then eventually maybe the radiator. The car will be a permanent fixture as a family member, so replacing parts isn't a huge deal breaker. When this motor goes, hopefully not for a while, I'm planning a RS6 swap. Car has 110k on the clock, and runs like a champion otherwise. Any help at this point would certainly be appreciated as I've run into a metaphorical wall when it comes to diagnosing and fixing this issue. Thanks in advance!

[mik15]

T-stat was the culprit in my case for fans running crazy...

[Bigglezworth]

If your coolant sensor wasn't at fault, the next item would be the thermostat. Anyone experienced with putting the car in to service position can perform a T-stat swap in 2.5hrs.

[Codinc]

Thanks guys, I will move forward with the T-Stat next as it's a lot cheaper and common sensical than a new A/C fan, which I don't believe is the issue anyway. I appreciate the insight and will post the conclusion once it's done.

[905084]

If you need a good shop in the SLC I'd recommend Wendell at Alpine Motors. I started farming out stuff I couldn't or didn't want to do to him.

[Codinc]

I've ordered the 170 degree thermostat, instead of the OEM 190. The car usually runs really hot, so I figured it'd be a good idea to keep temps down. What do you guys think, as I can easily pick up the OEM one instead.

[RSoverAll]

Personally would stick with OEM temp. Cooler temps can affect open/closed loop performance, fuel mileage, and a/f mixtures.

Sounds like something is shorted to the fan circuit or something is commanding your fans to run all the time. In vagcom you should be able to see if the fans are commanded or or not. A fan is just an input device controlled with a relay and a switch, a lot like a light bulb.

Also may wanna check the upper and lower rad hose temps. That can help isolate an actual radiator cooling issue like blockages or clogging.

Does the fans turn on and stay on as soon as the engine is running or when you turn on the ignition switch regardless if the engine is running or not?

[DHall1]

Use only oem thermostat.

[4everRS]

I would run OEM tstat as well. If you're looking to run cooler, you might consider a better oil cooler instead.

[Codinc]

RSoverall: Yes the AC fan turns on as soon as the car does and it stays on 100% of the time, also it stays on at half power after motor is turned off for 10-15 minutes. This specifically, leads me to believe the T-Stat is the culprit, also the car runs passed center line (coolant temps) and towards hot with AC on, while sitting. But once I start moving again, temps come down. The other fans come on/turn off correctly based off of operating temps coming up and down through their respective ranges. My VAGCOM pulls no codes unfortunately.

Otherwise, as suggested, I've swapped out the 170 for a 192 OEM T-Stat and will be replacing it during the week this week. If this doesn't solve the problem, my next intuition would be the actual fan itself. However with this said, my optimism and the fact that I've replaced all other parts in the loop would lead me to hope that the T-Stat fixes the issue.

I really appreciate your feedback guys, and will definitely post an update when the new TStat is in.

[RSoverAll]

Alright. Well I hope that does fix the issue. Keep us posted.

[Codinc]

Ok. So I changed out the thermostat, still didn't fix the issue unfortunately. A/C fan is still in air raid siren mode..lol..but I did take it's cover off to make it a little quieter. Also, I took the fan off of a 2.7 donor car I have, and it's not the fan either. During the process, I noticed some coolant lines starting to come apart, so those have been changed with new ones. VAG pulls no codes. The thermostat which I bought, supposing to be "OEM", is an 87 degree Celsius, but the Wahlberg one I took out has an 82' stamped on it, so I'm kind of at a loss with that. I've run the car hard since, and all is well; However the coolant temp notches above center slightly, with car parked after getting up to operating temps. It's not passed the 1st line, maintains that temp and doesn't go higher. If you guys have any more insight it'd be helpful, as this is really a needle in a haystack situation. Thanks!

[RSoverAll]

My A4 did the same thing, temp gauge slightly past center and ran warmer when pushed in the heat of the day. My radiator and heater coil was clogged/clogging.