A8 D3 AC issues


I want your faulty electronics
I'm having issues with my AC and trying to find out what's wrong with it myself before I send it off to Audi or a local specialist first.

Here's my posts from another forum of what i've done and been doing.

Copying and pasting at its best.

The AC was never very cold on the A8 since I bought it and I've always put it down to the lack of gas.
I dropped the car off to Audi for a AC Service.
Picked it up and it was cold, drove home and was the same.
The weather was it as hit as it has been so I waited till it was really hot.
Spent the day in Bristol and basically the AC the ****e. Pumping out warm air and not cooling at all.

Got home and phoned Audi.
They basically said it tested fine but it's in for a AC service not fault finding, so they just gas it up, do the other bits and ship it off.
If it's not working I can drop it in for a diagnostic session at £50.
Sod that, I went off to talk to a AC chap I know.I have no idea why I never seen him first.
He suggested I replace the pressure switch first.
So I did, no difference.

When I put vcds on the A4 I could see what's going on with the AC system but for some reason vcds does not have a label for HVAC system for the 8.

Does anyone know what each message block does in vcds or another way to test the AC system?

I has gas, I'm thinking it's the pump that's gone now.


Picked up on monday, no change.
De-pressed one of the schroeder valves and there was still gas in the system.
Did the same thing saturday when I fitted the pressure switch and still gas.

A output test via VCDS should start the fan up?
I'll do that later.


I might have some free time this week to get out to the car with VCDS and test/scan the system again and I don't get any further I'll drop it off to the local AC guys.

I can't do the leak test cause I don't have a sniffer, the glasses or the light, so its all VCDS.

Things to test:
AC fan.

That's all I can think of.
With no label file for VCDS its hard to check the meas blocks.


VCDS Block Reading for A8 D3 HVAC


Going by that my system is gassed up and working fine from that side of it.
The pump spins, the fan kicks in when I do a output test but not when the system is running and there's the correct pressure or at least its in tolerances.


I'm out of ideas. lol

I made a custom label file today and tried it out.
It worked and it kind of helped.

Going by group 002 the compressor is switched off.

3 = Compressor OFF by Pressure Switch : Basic settings not performed
12 = Compressor off by Requested from ECU

Not sure what 12 is apart, apart from the above explanation.
At least number 3 might be something I can do.

I went to the basic setting and started.
Learning started.

Learning Ended.

Made no difference.


I got 1 number wrong.
I missed off number two in the custom label file.

2 is pressure switch.
3.0 is "Display 3 Compressor off (pressure in refrigerant circuit too low)"

But then group 1, display 4 says this "Pressure in refrigerant circuit in bar Calculated by Climatronic Control Module J255 via duty cycle of signal from High Pressure Sensor G65 display = less than 2.6 bar or greater than 29 bar (even briefly) Pressure in refrigerant circuit too low (system empty) or too high High Pressure Sensor G65 malfunctioning display = 2.6 bar to 29 bar Pressure in refrigerant circuit in permissible range"

So its not too low going by the pressure sensor switch.

It says this
"If a compressor switch-off condition exists for the compressor (ı display group 002) the A/C Compressor Regulator Valve N280 cannot be activated, nor during output Diagnostic Test Mode (DTM) ( Output Diagnostic Test Mode)."

I'm not sure what it means by this in the document about the display zones.
Zone 2, Last compressor shutoff criterion Explanatory notes
Zone 3, Last but one compressor shutoff criterion Explanatory notes
Zone 4, Third last compressor shutoff criterion Explanatory notes

I kind of want to side with low pressure but its saying its not low pressure.
So what is it or is it getting it from somewhere else?


And that's where I'm at now.

Anyone got any idea?


Well-Known Member
VCDS Map User
Are you getting hot air only from the air vents? My AC as working fine with no fault codes, but I was get very hot air out of the system. could be the same pump that failed on my car, or could be one of the vent motors controlling the air flow which direct the air to either the heater matrix or the air-con matrix.


I want your faulty electronics
The air is coldish depending on outside temp.
The air direction and motors seem to work.

Having a sleep on it, I think it might be leaking but the last two cars that had leaks worked for a couple of days with a leak.
I'm going to get it to a AC place tomorrow and check for leaks.
I'm not sure what else I can check.


Well-Known Member
VCDS Map User
You would get a low pressure warning on the hvac module if it was low on gas. My guess is flaps controlling the air flow is the fault here.


I want your faulty electronics
I thought I would get some error code if it was low on gas but group 2 blocks 2, 3 and 4 shows the pump has been switches off due to the ECU and low pressure.
The vents do pump out cold air but never AC cold air.


Well-Known Member
VCDS Map User
Sorry Scott out of ideas on this one, if the pump was switched off due to low pressure then you would think you would have a fault code. Very strange :uhm:


I want your faulty electronics
That's my thinking mate.

Got back from a local AC place, they regased the system, it passed the leak test but with their machine still attached, engine running and AC on, the needles on their gauge never moved.
Apparently they should move or fluctuate when the compressor is working.

Looking at ELSA, the only bits left to replaced that could cause the AC system to stop is the pump.


Well-Known Member
VCDS Map User
Looking at elsawin on the A6 3.0TDi some of the coolant pipe are in the way of accessing the aircon pipes on the pump, so you have to drain the coolant system. Hope the A8 is different.

Alex G

Registered User
Hey Scott, wondering if you ever resolved this a/c issue?
One thing i could tell you is i think you're suppose to be looking at only the first box in Group 002 of VCDS Measuring Blocks for Address 08 (HVAC)
in your case it indicated a zero therefore your a/c pump is on.
I have the same issue on my 08 A8 now, it's an FSI so the a/c compressor is tucked away and there is no magnetic clutch from what i understand, when i hook up pressure gauges to the low and high ports of the a/c and then turn on the system the needles barely move.
no fault codes, pressure sensor is within range, any ideas?