S3 8L Air Con Problems - Possible Compressor Failure?

[AJD S3]

Hi all,

Decided to venture down to KwikFit today. Needed to have my Air Con re-gassed and serviced, something I'd been putting off for a while, but in light of the recent hot weather we've been having, my car has been about as comfortable as a Turkish prison.

After them attempting to re-gas the system twice, my air con still wasn't blowing cold. Some further investigation showed that the clutch on the compressor wasn't dropping, which would explain why. KwikFit instantly diagnosed this as the compressor itself being knackered as you might expect. They explained their machine had shown no leaks in the system at all, so the compressor must be the cause.

So off I go round the corner to see my friend Gordon, where we started our own little investigation into the issue.
We did the following:
- Checked the fuse on the top of the battery cover, which was completely blown, so changed it for a new one.
- Disconnected the compressor electrical connector clip, and reconnected it.

Unfortunately, neither or the above rectified the issue. We then checked for any logged errors with vagcom, and tested the pressures, all seemed fine.

Long and short is, none of the above resolved the issue - my car is still a sauna.

So is this down to a knackered compressor, or could there be any other causes?

 

[chris.sargent]

Is the compressor clutch engaging when you turn the ac on? If not, does it engage when you apply 12v directly to it?

 

[AJD S3]

Is the compressor clutch engaging when you turn the ac on? If not, does it engage when you apply 12v directly to it?

It doesnt sound as though it is, I presume I'd hear a clunk sound from it if it was?

How would I go about putting the 12v straight into it? Not sure how I'd do that?

 

[AJD S3]

BUMP?!

Sorry to push this back up to the top, but I could really use some advice on it! Thanks guys!

 

[Ste_Nova]

even if the comressor was dead the clutch should kick in if no pressure faults etc are showing

 

[AJD S3]

even if the comressor was dead the clutch should kick in if no pressure faults etc are showing

The clutch is part of the compressor though? So even if the clutch has gone, sounds like it has as it's not engaging, still means a new compressor to fix really?

 

[chris.sargent]

Hi AJD. Sorry I was travelling all day yesterday so no chance to reply. If it is just the clutch that has gone it is actually possible just to replace it seperately.

What you need to do is work out whether the clutch is not engaging as a result of being faulty or as a result of the system not letting it engage because the conditions aren't right to do so. It's important to do this because if your compressor has chewed itself up then that is bad - the air con is a closed system with lots of components each one of which will be storing all the metal debris that your broken compressor just kicked out. A simple replacement of the compressor is really not an option because it will get killed again relatively quickly by all the debris in the system. In would be like rebuilding an engine using oil from one that just blew itself up. If the compressor has gone you will need to replace a number of other components and have others flushed through with solvent under pressure to clean out the system - not an easy / cheap job.

To be honest, if you don't know how to apply 12v to the clutch to check it's working then I'd suggest you should probably seek out an A/C specialist (not just someone who does re-gasses!) who can test all the system for you. It will cost a little bit more but it will be worth it - the air con system is pretty complex so unless you're a competent mechanic with access to a few special tools (set of dual pressure gauges, flushing system etc) then it will save you money in the long run.

However, in the spirit of DIY it is fairly easy to check the comp clutch is working! To test it, you need to disconnect the plug on the compressor and apply 12v directly to the wire that goes to the compressor. I'd recommend you use a spare battery if you have one. Take a jump lead and connect the -ve side of the spare battery to your -ve battery terminal on the car. Then take another jump lead and connect from your spare +ve terminal to the plug that goes to the compressor. If the compressor makes a clunk / click then the clutch has engaged.

You can report back what you find. Has the fuse blown again since you changed it? Do you have a multi-meter?

 

[AJD S3]

Hi AJD. Sorry I was travelling all day yesterday so no chance to reply. If it is just the clutch that has gone it is actually possible just to replace it seperately.

What you need to do is work out whether the clutch is not engaging as a result of being faulty or as a result of the system not letting it engage because the conditions aren't right to do so. It's important to do this because if your compressor has chewed itself up then that is bad - the air con is a closed system with lots of components each one of which will be storing all the metal debris that your broken compressor just kicked out. A simple replacement of the compressor is really not an option because it will get killed again relatively quickly by all the debris in the system. In would be like rebuilding an engine using oil from one that just blew itself up. If the compressor has gone you will need to replace a number of other components and have others flushed through with solvent under pressure to clean out the system - not an easy / cheap job.

To be honest, if you don't know how to apply 12v to the clutch to check it's working then I'd suggest you should probably seek out an A/C specialist (not just someone who does re-gasses!) who can test all the system for you. It will cost a little bit more but it will be worth it - the air con system is pretty complex so unless you're a competent mechanic with access to a few special tools (set of dual pressure gauges, flushing system etc) then it will save you money in the long run.

However, in the spirit of DIY it is fairly easy to check the comp clutch is working! To test it, you need to disconnect the plug on the compressor and apply 12v directly to the wire that goes to the compressor. I'd recommend you use a spare battery if you have one. Take a jump lead and connect the -ve side of the spare battery to your -ve battery terminal on the car. Then take another jump lead and connect from your spare +ve terminal to the plug that goes to the compressor. If the compressor makes a clunk / click then the clutch has engaged.

You can report back what you find. Has the fuse blown again since you changed it? Do you have a multi-meter?

Hi Chris,

Thanks for the above. I'll try your suggestions once im back from the US in 2 weeks time. I know that at the moment, after a few seconds of the car being started, the revs drop as the air con kicks in, and a very slight noise can be heard at the same time as this drop.

Mind you, this has only happened since I changed the fuse, air seems a bit colder from the air con than before, but still doesn't anywhere near cut it in the heat. Could this mean the fuse has possibly fixed the issue, and now it just needs a regas having not been in operation for so long whilst it's been broken?

 

[chris.sargent]

Possibly.... - if the revs drop and you hear the compressor kick in then it the clutch is probably fine but doesn't necessarily rule out a tired compressor. Also,depending on how they recharge it, sometimes the compressor needs to be running to get a full hit of gas. Take it to an A/C specialist to recharge it - if it still doesn't work properly, they'll be able to diagnose any faults a lot more accurately using their dual pressure gauges - a faulty / tired compressor will show up on this. Hopefully they can sort it with a simple re-gas or they might just recommend getting a new receiver / drier fitted.

Do your cooling fans come on?

 

[AJD S3]

Possibly.... - if the revs drop and you hear the compressor kick in then it the clutch is probably fine but doesn't necessarily rule out a tired compressor. Also,depending on how they recharge it, sometimes the compressor needs to be running to get a full hit of gas. Take it to an A/C specialist to recharge it - if it still doesn't work properly, they'll be able to diagnose any faults a lot more accurately using their dual pressure gauges - a faulty / tired compressor will show up on this. Hopefully they can sort it with a simple re-gas or they might just recommend getting a new receiver / drier fitted.

Do your cooling fans come on?

Hi Chris! Thanks for this.

The revs definitely drop and the flow of air changes through the vents, so I definitely think the compressor is kicking in.

When KwikFit went to recharge it, they had it on a dual guage machine, which showed no leaks or faults, however they just left it sitting there, engine off, pumping gas into the system. I'd have thought it'd need to be cycled through at least, in agreement with what you're saying. After changing the blown fuse, I went back round to KwikFit, as it had started to feel colder, and I wanted them to try the recharge again. They said there was no point as if it was working it would be blowing far colder air than it was, even though they hadn't actually recharged it on either of their attempts?

The blower fans work fine and always have done, it was only the compressor that's been mucking about really.

 

[chris.sargent]

Okay, so they probably had an automatic recharge machine which I don't think needs to have the engine running - it empties the system, creates a vacuum for 30 mins to boil off any moisture and then pumps in a measured weight of gas and oil. In a healthy system that's already working, this normally works perfectly fine.

However, the fact that it's still not working right means that something must be off! The dual pressure gauges allow you to measure the pressure in the pipes either side of the compressor (effectively). There is a lo-side and a hi-side. The compressor pumps from the lo-side in to the high-side. If the compressor is not pumping efficiently, the pressure in the hi-side will read too low. If the seals in the compressor are failing the pressure in the lo-side will read too high (because the gas from the 'pump' is not going to the right place). Both these faults can be diagnosed by a competent A/C specialist and will tell you whether your compressor needs replacing (Trying not to be too generalist but I'm afraid the Kwik-Fit guys and other simple recharge places probably don't have the expertise to make an accurate diagnosis - they just plug in the machine and if it doesn't work, then that's the limit of what they can do)

There could also be other faults such as a blocked receiver / drier (hi-side pressure too high) or the thermostatic expansion valve could be faulty / blocked (lo-side pressure too low) - both of these faults could again be easily diagnosed by an A/C specialist as they will show up by not having the right pressures on the hi and lo-side.

All of these faults could also be caused by not putting the right amount of gas and / or oil in too. Having too much or two little gas and / or oil will ensure your compressor has a pretty short life so you have to be REALLY confident in the place that does your recharge.

By the way - when I said cooling fans, I mean the ones in the engine bay that blow over the radiator and condenser, not the blower fan in the car.

p.s. I'm not an A/C expert or specialist but I have had a failed compressor spill it's internals in to the system on another car so I spent a lot of time reading up about it so I could do a proper DIY without worrying about the new compressor failing again.

 

[AJD S3]

Hi Chris, thanks for the response again, I'm really grateful for the amount of time you're putting into this, your advice is incredibly helpful.

Thanks for the above, my question is though, if the fuse had just been the cause of the issue first time around, would KwikFit's vacuum approach towards a recharge have worked? Im guessing it would have done, and no faults would have been shown.

I'll try and find an air-con specialist I think, as much as I am fairly technically competent, to the point where I can fit nearly anything on a car, this is just too complicated for me! I think I'm just going to have to reach into my pocket for once and pay someone who knows what they're doing!

I'll let you know how I get on Chris

 

[chris.sargent]

No worries. I try to do everything DIY too but with air con the tools and stuff are quite expensive and, unlike most other tools, I fear I'd only use them once. You can get a set of gauges for around £50 but if you found anything wrong then you'd still have to take it somewhere to get it emptied, do the work and then take it back to get it refilled anyway. In the long run, I think it just makes sense to go to a specialist who really knows what they're doing and has the right tools.

Good luck and let us know!

 

[chris.sargent]

As for the question about the fuse, I don't think it would have made a difference to their re-charge but it does kinda show how good their troubleshooting is!

 

[gary3306]

I do aircon at my work and Chris has given you some sound advice there. It does sound like your system is workins as such, but not cold enough. One of the biggest causes of this is the need for a new receiver/drier and condensor (at the very least a new rec/drier. They should be done as a pair really, and it's very bad practice to renew a condensor and not the rec/drier. Its like renewing brake discs and putting the old pads in). Then the system should be vacuumed down for at least an hour to boil off any moisture. Chris mentioned about putting too much or too little refrigerant in; if you put too much in, the system will kick in and immediately out again as the high pressure switch switches the system out. This will happen continuously, so if the clutch is kicking in and out constantly, it's overgassed. If there's too little, the low pressure switch will stop the system working all together to protect the compressor.
I would try getting a new rec/drier fitted by a specialist, having the system vac'd down for an hour or so and then see what it's like. If everything else is checking out as ok, then this is where I would be looking.
Hope you get sorted.