Intermittent A/C fault.

[Lodhiz]

Afternoon All,
Hope you're all well. Just stumbled across an issue I am having with the A/C on my 2001 S3. It appears that whilst at a stand still (with the car on), the temperature of the blowers is very mild as opposed to the very cold air I would expect. However, when on the move (around 20 MPH) the blowers spring back into the life, blowing freezing cold air again. Whilst coming to a standstill, the air remains cold for a few minutes and then returns back to the mild temperature again. I can confirm that there is Gas still in the system, as I had the system re-gassed again to no avail.

Now I have replaced the radiator fan fuses and can confirm that both Radiators spin when setting the climate control to 'LO'. Having done some research, people had mentioned the Compressor potentially having a bad earth connection (not 100% sure about this), or the Condenser (radiator?) requiring a good clean with a jet wash. Now, I am confused; initially I thought that the Compressor/Condenser are the same thing? Apparently not, or so I'm lead to believe.

Further more, using VCDS, it didn't mention any HVAC issues/codes.

Am I on the right track by trying to clean out the condenser/radiator (looks like a radiator to me)? Or is there something else that I am missing, or should potentially try?

Any help is appreciated. Many thanks.

- Lodhiz.

 

[Lodhiz]

As a side note worth mentioning, my alternator clutch/pulley is on it's way out if that could contribute to this issue at all?

 

[newbster]

meh, sounds like a weak compressor, needs lots of revs to generate enough pressure
you could try cleaning the condenser, which is the thin rad in front of the main rad, but if it was that blocked I would expect to see coolant overheat as well

try revving to about 3000 rpm when stationary, see if the cooling comes back

best bet is to find a good AC specliast who can diagnose it properly. you need a set of gauges to measure the pressures,

ac system, ignoring all the little fiddly bits

compressor, big spinny thing by the alternator, compresses gas back to liquid(hot)
condenser radiator in front of coolant rad, cools hot liquid
evaporator, in the ductwork of the dash, liquid boils back to gas and gets cold, cools air passing through it going into car
return to compressor

 

[daithi23]

I work in an air condition factory, the above is correct, and I've had the lads here check my car too. It's such a simple job to service them that I can't figure why it costs so much to get it done!

 

[Lodhiz]

Sorry @daithi23 when you said the above is correct, were you referring to cleaning out the condenser at the front of the car? Or did you mean it could be a weak compressor?

Also at your place of work, when carrying out an AC service, what does that usually comprise of?

 

[daithi23]

I was more referring to newbsters explanation of how it works, but I would firstly give the condenser a clean out, that shouldn't really be an issue though unless you've been driving through sludge. Then after that you're probably better off taking it to a place that can do a full service.

We do big industrial units here (such as stadiums, hospitals etc) but the guys have done car air con in the past. What your typical service if someone comes in (to a proper place, not here) is just top up the gas and check the temp at the vents. If something seems wrong the gas will be vac'd out, pressure test done to see if there's a leak, then fill up with new gas.

Mine was a little warmer than my previous car so I had them take a quick look, but it screwed with it totally, I think there was too much gas so we let some out. Now it's still where it was so what I really need to get done is drain all of the gas and have it refilled.

 

[newbster]

lodhiz, reading you post again, you seem to imply the condenser fans only came on when CC was set to LO, that would be wrong, they should be spinning whenever the AC system is engaged ( ie not in eco mode)
the cooling fans not running would cause your symptoms

as would a weak compressor, have you tried increasing revs to see if it starts to cool again, its cheap and easy to do

AC systems are pretty simple, but you need the right tools for anything past basic checks, a set of pressure gauges is essential, as too much gas is as bad as too little, as daith found out

misquoting tuffty, its all about the pressures

 

[Lodhiz]

Thanks lads for the explanations.

Newbster - my radiator and condenser fans are fine. They both kick in whenever I set the temp to around 20c and lower. I had read elsewhere that overtime condensers can get clogged up (baring in mind my car is now 14 years old) so I wanted to give that a clean but I'm not sure what is the most effective method. Trailing back to my 2nd post, I also mentioned that my fan belt and alternator clutch are in need of replacement, so I have a feeling this may possibly be a contributing factor. When looking down at the alternator and compressor, it looks like the compressor pulley is 'wobbling' (I haven't actually touched it by hand though) so as you previously mentioned it could be a weak compressor, but they're a little on the pricey side for me at the moment.
But yes, increasing revs; particularly to around the 3k mark will cause the car to start blowing cold air. When idling it's still cold, just not AC cold.

 

[newbster]

ok
"But yes, increasing revs; particularly to around the 3k mark will cause the car to start blowing cold air. When idling it's still cold, just not AC cold."

so it more than likely a weak compressor, but could be low on gas

I doubt its the pulley, if it was wobbling to the point where it was slipping, you would hear and smell it as it would get very hot

do a goggle on local a/c specialists, I have found mobile ones to be good value, they should throw on a set of gauges and be able to diagnose the issue.


hope you get it sorted

 

[Lodhiz]

Cheers buddy, I'll let you know how I get on. Once again, thanks for the advice.

 

[newbster]

where are you located, I know of a good guy in the solihull area

 

[Lodhiz]

I'm based in Birmingham Newbster so Solihull isn't far at all. If you could PM the details for your guy, i'd be more than happy for him to take a look based on your recommendation.