Air con switching on and off randomly

[mrchivs]

I have an Audi A3 1.8T (1999) with climate control and have been having issues with my air con that seem to be getting progressively worse over the last few years. Firstly I've had it regassed twice now but it doesn't make any difference. If the A/C is set to Auto and the temp set to LO (i.e. below 18 deg C) iit will blow cold air for a certain amount of time, but then something cuts out and the air is back to ambient temp. After around 30 mins it might go back to blowing cold again, but its fairly random when it happens or for how long the cold A/C lasts.

Have tried fiddling with the A/C on/off button when the air is not cold and you can hear the air compressor rev up but soon dies down and no change in the air temp. If you just leave it set to Auto it will eventually start blowing out cold again, but this could be after another hour of driving.

I don't think this is a gas pressure problem (but I could be wrong) as when its blowing cold, its really cold. I suspect its some kind of sensor with an intermittent fault thats failing to trigger the air con compressor to activate properly.

After the last regas service it worked fine for a few days, but again started cutting out. I no longer work near the garage so did not go back to them.

If anyone has any idea what could be wrong here (gas, switches, sensor, loose connections?) please let me know your thoughts. I will try taking it to another garage and see if they can do some fault finding, but the chances are it will be working when they test it.

 

[Staz]

Could be more than one answer to this but my first suspicion would be a blocked evaporator stopping the air flowing through it freely . Any air passed through it would still be cooled but the volume of air would be reduced, have you noticed this at all?

If there is a blocked evaporator the refrigerant cannot be heated back to a gas quick enough and it causes a restriction to the flow of refrigerant around the system. Eventually the high pressure cut out trips and the air con system is disabled. Eventually the refrigerant warms up again and the system restarts.

The first thing you should do is get any fault codes looked at as that'll give a very good steer.

 

[mrchivs]

OK, I've tried removing the pollen filter as thats not been changed since I've owned it (5 years), so maybe that has been restricting the air flow. Strangely it worked fine today for a whole hour non stop, but the air temp was only 22C outside, so I guess the compressor did not have to work as hard as yesterday when it was +30C. I will see how it goes this week, maybe a new pollen filter is all thats needed (the old one was really clogged up). Have it booked in with an Audi dealer next week for a diagnostic test, so if there are any faults hopefully they will know exactly where it is.

BTW, i can't locate the evaporator itself, is there a logical place for this (eg near the radiator)?

 

[Staz]

The evaporator is hidden inside/below the dash. It depends on the car as to how well you can see it but I suspect on a modern car you'd struggle!

Was the drive today with the temp set to low?



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[mrchivs]

Thanks, after a quick look through the Haynes manual I can see the evaporator is under the dashboard (behind the glove box). Can't see how anything else could be blocking it as it would have to get past the pollen filter, no sign of leaves or anything in the air intake. Wasn't warm enough this morning to have the air con on for the full journey, but was working when I started the car. Will see how it goes over the next week with the pollen filter removed. Cheers!