AC compressor won’t turn on 1994 RS2

[Verruckt]

Hi! I’m having trouble with the AC in my RS2. The climate control buttons were messed up, so I got a new unit from Audi Tradition thanks to Europrice.us. The system was recently recharged, and it did run for a little bit using the old climate controller, but then stopped. Swapped in the new controller and still the compressor won’t kick on. Not sure what to check next, is there a fuse diagram for the under dash? Anything else I should look at?


I read here about low system pressure and the compressor won’t turn on. Even though recently charged, should I have it checked again?

it also mentions a pressure switch, where is that located?

https://www.s2forum.com/forum/techni...on-in-rs2-help

[Antsa]

There is hidden diagnostics menu in the ac headunit. You can use it to determine the reason why the ac is not engaging. Do the following.

Press and hold the manual recirc button. Then press the manual flow control up (arrow up) button. You should now see 01c on the temp display. Use + and - buttons to navigate to channel 52. Then use this attached picture to solve the reason.

Edit: after you see "52" on the temp display, press recirc button to enter the channel. After you are done, you can exit the diagnostics menu by pressing "Auto" button.

Screenshot_20240714-092944_Microsoft 365 (Office).jpg

[Verruckt]

Thank you, Antsa. I will give this a go and report back.

[johne]

The most likely reason for aircon not turning on is that there isn't enough gas in the system. If you've got access to an aircon pressure gauge check the pressure in the system with the engine off and everything stationary. Should be around 45psi. If it's below 20psi then the compressor won't turn on.

Another option is to get to the A/C low pressure switch wiring and see if the switch is open or closed. The switch itself is difficult to get to as it's sandwiched high up on the passenger footwell above where the ECU goes, so it's best to connect to it where the switch wiring comes out for the climate controller.

[Verruckt]

I have some updated info, have a tech that is checking all the wiring and sensors.

Climate control module not sending a ground signal. I have multiple CC modules, each one is giving the same results. Remove the module and provide ground and the compressor turns on and is blowing cold.

Amb air temp sensor (working)
Headliner air temp sensor cabin (working)
Dashboard air temp sensor (working)
Recirculating air temp sensor (working)
Fresh air blower temp sensor (bad?) Any idea where this is in the car? It is reading zero.