A6 Air Conditioning cylcles on and off, warm moist air, then cold air - what's wrong with it?
 

This is in humid 95 degree heat in sunny Mississippi. I just moved here from Sonoma, CA, where the A/C hasn't had much workout (bought this car freshly 'Assured' last winter).

When it comes on, sometimes it is nice and cold, like it should be (really very cold) but the next minute it spews moist humid air, whether the 'auto' switch is engaged or not (no, not using the 'econ' switch).

Also, the temp guage on the car is is just short of dead center (on the cool side) so it wouldn't seem to be for purpose of overheating protection.

There's no reason for it to be shutting the a/c off, as it is very hot and sunny, e.g. the system is not overperforming the 'temp' setting of say 68 degrees. I have noticed that the a/c cuts off under full acceleration, but assume this is supposed to be this way (like my prior 90q20v). However it still cuts on and off even if you're just sitting still or ambling slowly around a parking lot. I can hear what must be the condensor cutting on and off, along with the cold to musty warm air change.

I have an appointment scheduled for other things next week, so I'd like to get this resolved, but I think the dealer may need some direction on this to be sure it gets done right (they are "swamped right now" and "everything is being rushed through to clear up the back log") They sell VW, Audi and Jaguar, so I guess the service department makes money.

So what's the deal with this a/c?

Thanks in advance for taking a stab at it!

That's the compressor cycling. Probably low on freon (or whatever they call it now).

I've never had that, but then weather here is a bit kinder. Sounds like it needs servicing.

It's "Assured" so my debate is whether to ask the dealer or take it elsewhere if it's only low
 

If it's only low on freon I may just take it elsewhere. I suppose the best bet is to have the dealer look at it and then decide. It seems it would be something more than low on freon.

Any explanation for why it would cycle on and off even though it's bloody hot outside? I wouldn't think it should be cycling on and off at all - 95 degrees on a humid sunny day in a black car is cause for more than a marginal need for A/C - e.g. cycling on and off...

Or is that normal A/C operation?

If it is low on "Freon" I think that there is a sight glass
 

(ok I'm showing my age) near the front of the car. Try to see if there are bubbles in the sight glass. If so, you're low. (sorry!)

It cycles when low because....
 

...the low pressure switch shuts the system off to protect the compressor. After it sits for a short time the pressure rises and the compressor starts again. The cycle just repeats.

If you get low enough on freon the compressor won't start at all.

Take it to a dealer to get it looked at. Audi's require a special machine to add freon.

Re: A6 Air Conditioning cylcles on and off, warm moist air, then cold air - what's wrong with it?
 

I have the exact same problem on my '98 A6 2.8. On the freeway it cools fine, but in city traffic, when the outside temp is hot, the compressor cycles on and off. I have had it in to an a/c place 3 times - they say there is a small leak (5 oz. over 2 weeks) but they cannot find a leak after putting the dye in. The freon cannot get low unless there is a leak. Anyway, appreciate hearing from you if you find the cause and the solution.

You are right it is low on freon causing the low pressure switch to ...
 

...cycle the compressor on and off (cold air then hot) However you do not need anything other than a standard R134 automotive connection to charge the AC. I have done it myself and for some reason have become the local neighborhood AC expert. (I have fixed 4 different AC systems in the last few weeks) I think it helps that I am in the Temperature controls business and own a set of gauges! I reccomend having a knowlegable AC mechanic determine what the problem is. I had one auto mech tell me my system was fully charged, and it wasn't, I had another tell my wife the whole system needed to be replaced in her car and all it needed was charging so be careful and don't always believe what they tell you is the problem. One thing about 134A is the pressures may look good when the outside temp is cool but then on a hot day they are low. It is also may need to be evacuated if there is moisture in the system and then recharged.

Thanks to all of you for the collective information. One final question before I have the dealer
 

give it a look next week:

If it is low on R134 (assume this is what's in it, not "freon"), does that automatically mean there MUST be a leak in the system?

If so, I want to really push the point with the dealer because the car is Audi Assured and I want to be sure it is taken care of correctly under warranty, and that it is done while it is still summer (e.g. a simple recharge might make it through the rest of summer even with a slow leak) and then I end up footing the bill later for a repair that should have been made now.

Any thoughts on this? Low juice = leak, no room for 'evaporation'?

Thanks again. I will post the dealer's recommendation after it goes in on the 12th.

Regards,

Sarge

AFAIK low juice = leak. It's a sealed system.