kithrax

New user here and need a bit of help from some vets.
2004 Audi A6 2.7t 6 speed

Driving down the interstate my a/c fairly quickly went from cool to blowing hot air a couple of days ago. ECON is not active on the system.

I can verify that the a/c clutch is not engaging and fan behind the condenser does not spin when a/c is on.

Low pressure port to A/C shows high pressure, doesn't mean much if clutch doesn't engage (I believe)

I have an ELM327 wifi OBD2 scanner that does not show any fault codes.

Did a LOT of forum searching to find a ton of similar issues but I believe I am on information overload right now.

My obd2 scanner does not seem to have access to HVAC diagnostics and some VCDS/VAG tools I've read state they can run AC diags.

I have checked the fuse box inside the cabin and could only make out 2 fuses that dealt with the A/C (they are fine), however I don't speak/read german and my diagram is completely in german.

If the condenser fan is not running would that tell the system not to engage the clutch?

Any troubleshooting help is appreciated, I drive in 102F weather on a daily basis here. I will update through to completion on this forum.

georgeb944

The full version of VCDS will allow output testing of the AC clutch electrics. That said, failure to engage the clutch could be the AC head, the AC relay, or the 10 pin connector in the engine compartment or the wiring between them.

tester123

As mentioned already, need VCDS (i.e.ross-tech). In mean time, check fuses? Sure if enough refrigerant is there?

SloopJohnB@mac.com

Audi AC is pretty trouble free for the three I've had, only had to keep adding a leak sealer/R134A+ to my 2K4.2A6 every spring for a couple years and then it worked fine. The new R134A systems have specific quick-disconnect ports for LP and HP; you'd need specific adapters for an older R22/R134A manifold/hoses or new R134A hoses with the right adapters. Refrigerant kits often have just the LP adapter, which shows the LP reading. I've used ArcticFreeze for one.

You should probably have a static pressure of around 20psig in order for the compressor low side switch to enable compressor operation.

This may help:
Troubleshooting with Gauges FAQ

kithrax

Just got home, temp outside is 96 when taking this shot. This is a can of a/c pro with a basic valve attached. Reading somewhere halfway between 55 and 100 as you can see.

Can't get a VCDS until my budget can allow it. I'm not sure if auto stores carry any freebie diagnostics on this.

I've read in other forums that this PSI rating could be because the system is not engaging and is equalizing pressure from the high side but what do you think?

I could vacuum the pressure into an empty Co2 tank in the garage if you think that this is keeping the system from engaging. Then I would question how the system got higher in charge.

I did not fire any refrigerant from this can into the system as I saw the needle in the red.

kithrax

George, is there a way to isolate an issue without VCDS for now? Is one more likely to fail or a way to test the individual components?

georgeb944

The wiring diagram for your car should show you how the individual components for the AC clutch are connected. If you disconnect each one you should be able to test each one individually. In order to test the relay, you will need both a 12 volt power supply and an ohmmeter or a test light.

indoor

If your compressor is jammed there is no way to figured out through VCDS.
I would take the serpentine belt off along with the viscous fan(reverse thread). Take the compressor clutch bolt out(10mms, normal thread) If it comes out easily without holding onto the clutch, most likely the compressor is jammed. Be careful not to loose the spacer inside the clutch.Then try to spin the clutch by hand or with a strap wrench. If it doesn't spin you need a new compressor.
If it spins you need to run leads from a car battery. Plus (+) goes to the green wire. It is a strange skinny long green connector that goes in the connector area by the power steering fluid reservoir. And ground(-) goes to the case of compressor. Then test if metal sticks to clutch. If it does, the problem is somewhere else(bad high pressure switch, etc). If the clutch doesn't become a magnet when 12V(from a car battery) is applied to the green connector and compressor case, you have a bad electromagnet. The electromagnet has a thermofuse inside that can burn out when compressor gets jammed. But you can change out the electromagnet as well as the clutch without opening the system or without removing the compressor. I did it, but I had the front of the car off. It is possible to remove the A/C pulley without service position, but it is super tight and service position doesn't take that long...For the pulley removal you also need snap ring pliers (and for the electromagnet).
http://workshop-manuals.com/audi/a4_mk1/heating_ventilation_air_conditioning_system/heating_air_conditioner/air_conditioner/servicing_magnetic_clutch_-n25/nippondenso/denso_compressor/

kithrax

OK, new info.

I was mistaken on the a/c fan. AC fan does turn on when AC head unit is on. I have located relay 267 to the clutch. How do I bypass this to see if the clutch engages just for a quick test. 4 pins, socket has two copper gator clips and 2 aluminum gator clips


--------{} Copper

{}Alu_____{}Alu

--------{} Copper

Prospeeder

First go to the green 1 pin connector right by the powersteering reservoir and apply 12v to it. Does the compressor come on? If not, check the wiring from that to the compressor, if good, the compressor clutch could be bad.

Of course check if the green wire gets 12v when the a/c is switched on. If no voltage Check the relay next, you can check if the ground is being supplied to terminal 86, and 12v is at 85. as well as 12v at terminal 30. Jumping 30 and 87 should turn on the compressor.

If the ground is not being supplied to the relay, that means the system is preventing compressor function for some reasion. Vag com would really be needed at that point. Anything from ambient temp sensor out on the bumper to the a/c pressure switch could be keeping it off.