mkchang

Couldn't find anything about this searching, so here goes.

I know my AC works because it will blow cold air, except it will intermittently stop blowing cold air. Sometimes turn it all off then back on will kick start it, sometimes not. I've checked the freon level with one of this aftermarket guages and everything looks normal.

I see no codes, so I'm at a stump on why the compressor cuts off.

I saw somewhere that there was a way to see on the Vag-Com the state of the compressor, but I can't find out how to get to that area of the software.

Any thoughts?

MP4.2+6.0

Yes.

And preliminarily and said directly, it has been covered by posts, a lot of them. Literally just reading down the board to this Spring and you would find yet more, so I know they are there. How about trying that? Or, pretty basic search that drives my kind of reaction if I am direct. AW search is crap much of time as many of us know, so hopefully using Google BTW. Basic search example

Forget the can of refrigerant approach. Cheap, until you blow up compressor or its failure mode pulley. Sure, first can didn't work, lets throw in a little more... And if you have an FSI motor by chance then multiply damage cost by two or three. $30 may seem fine, until its 20-50x that to get replaced.

You say nothing about age of car, motor or location. Start by reading sticky. Content suggests to me you didn't--or at least didn't heed it--again being direct. But to get to punch line, pay the money and get system evacuated and refilled professionally. It is done by weight. If it leaks off less than half (which is less than many cans BTW), it starts to cut out. BTDT, so speaking from direct experience--and a lot of posts on this you should have found.

Can also be a sensor. If you are using real VCDS/VAG-COM with their cable, great. If its a rip off cable from Ebay, about as good as the feel good, unreliable can approach. Though all it does typically is not read most non-motor parts of vehicle, as opposed to risking blowing things up. If you don't even see the HVAC system, there's a clue about cable and such as well... And if you have legit cable, see the Ross-Tech site. Or if you don't still see it so you can see what you're missing.

mkchang

My bad, I have a 2009 A8L. Just found the documentation for the measuring blocks for the compressor shutoff codes, but the groups aren't labeled. Do you know which group it is?

the_duke

Again there are many, many threads about this issue.

MP4.2+6.0

Just use the programs pull down choices. Most common ones are in there. But compressor is basically "on"; duty cycle varies. No such thing as a clutch if you are working with that not applicable/old notion. Basically if you know it works at any time, compressor is working absent low percentage scenarios. If no codes, I would get refrigerant checked (emptied and refilled) professionally. That's the big percentage fix.

richard-tx

Take it in and have the system evacuated, the charge measured and the correct charge put in. You can't tell very much by using gauges. My guess is that it is either under charged or over charged. If the pressure is about 200 PSI @ 95 degrees at an idle, then that is about right. For best performance, get the correct charge put in.

ltooz_a6_a8_q7

until one day, it will turn it off completely. There are many tests. It cost me $45 and time to fix it. Yes, it did cost me $80 to take to the shop for evacuation and test.
If you hook up the ac manifolds and you have pressure on the low/high side, your system is fine.
Watch my video with the VCDS. Don't waste money on taking it to the shop for anything. You may have to replace your compressor according to their diagnostics.
In the last few days, the heat is @100F and my AC is ice cold.

https://www.audiworld.com/forums/a8-...r-g65-2900106/

Cheers,
Louis

richard-tx

Louis,

I believe your posting is lacking some data. Over charging can cause poor performance as can undercharging and it is possible to overcharge without throwing overpressure codes. It is really tough to get the refrigerant amount correct using gauges. So much depends on ambient temperature, humidity, idle speed, and to a lesser extent, other factors such as oil load, etc.

I think that the A8 system is close to being correctly charged when the high side is at about 200-225 PSI @ 95-98 deg F while idling with the windows open and set to "LO". If the high side is more than 225 under those same conditions, then it may be over charged. To accurately determine performance, get a Taylor brand thermometer. Other brands are notoriously inaccurate. If you get 50-55 degrees discharge at idle with the system set to "LO" with an ambient outdoor temp of 98F with windows open then that is about as good as it gets. On the highway, the discharge temp will be lower and as the car interior cools and the blower speed drops, the discharge temp will go lower still. About 40 degrees is as cold as it gets. While far from "Ice cold", it is adequate. Ice cold would be 32 degrees F. and that is undesirable. The danger of icing up the evaporator is too great.

Interior comfort levels can be dramatically improved with the addition of window tinting. Reducing the amount of sunlight on your skin and clothing almost always makes for a much more comfortable ride in the summer months. So the addition of some good window tint is, in most cases, a very worthwhile investment. I consider it a must have in North Texas.

ltooz_a6_a8_q7

Measured in temperature degrees, all terms are exaggerated. At 100f, I stuck a cheap thermometer in the vent, measured 47F and I did feel ice cold relative to the outside heat.
Anyhow, what I meant to say was understanding the root cause of the symptom before throwing money at it.
' sometimes it's ice cold and sometimes it's hot with the same temperature outside' - it's definitely not the freon in the system. What can turn on/off the compressor with fixed conditions?

richard-tx

What are the high and low side pressures?