Air con - fixed just in time for the heatwave

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Nobby
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Air con - fixed just in time for the heatwave

Post by Nobby » Wed Jul 20, 2022 3:50 pm

Hi all

A couple of years ago I posted about my air conditioning just not being that great. On a normal day it was fine, it keeps you cool enough to wear jeans and a t-shirt and it demists the windscreen fine when the humidity goes up.

Only problem was when it gets slightly warmer - say over 25 degrees - it just didn't feel quite cold enough.

The driver side vents always seemed to be a little warmer too so I've been looking at all sorts of things to solve the issue. Air con was regassed a couple of years ago by a local Auto HVAC place who were very helpful. At the time it seemed fine but the weather wasn't that hot. All the pressures seemed fine, no leaks.

In the post I will cover all the things I have tried to resolve the issue. If anyone else has problems then there can only be so many things to check. Some are easier than others. Some would be a nightmare last resort.

So. Where to start.....

Check for errors in VCDS:
If you have one available see what VCDS says. There may be all sorts of errors or none at all. But you can also use it to test parts or check output temps too.
Mine didn't have any errors - other than my air quality sensor - so it didn't help. The air quality sensor has now been replaced but didn't make a difference, I assume it will only affect whether recirc/auto recirc will do anything. In which case the recirc is best option to get the car coolest as in theory it gets colder and colder each time. I also didn't have any errors with my vent actuators/flaps. More on those later.

At this stage you should be able to confirm if the AC compressor is running or not. If it is and the pressures are ok then something mechanical isn't working properly.

Fans:
If your fans aren't working then you may show other issues (like overheating). The standard RS6 has 2 fans - 1 large and 1 small. The large one is pretty expensive as it has an inbuild controller, and the second fan is smaller but has a separate controller. When I first started checking my fans my smaller one didn't move. Hmmmm... I managed to find a second hand controller on ebay and plugged it in (located on the N/S front inner wing). Fan still didn't work. So I bought a replacement fan and this worked straight away. I've now disassembled the other fan and its working too so I have a spare. The theory now is that more air is being pulled through the condenser, taking heat our of the compressed refrigerant in its liquid form giving more benefits when it then gets turned into gas. This did seem to make a tiny difference, but not much. I think the other fan is so big that it manages to cool the RS6 sufficiently. Mine has never ever got over 90 degrees for coolant temps.

Heater box/flaps/evaporator:
The RS6 seems to have an odd design for the air conditioning (to me anyway). All of the air coming into the heater goes through the air conditioning evaporator. If this is bunged up it can seriously affect airflow. The air then goes through the heater core and out towards the vents. If you only want cold(er) there are 2 flaps which work in tandem. In the coldest mode air goes > A/C evap > vents. However the heater core isn't blocked off so some air goes past the AC evaporator to the heater core then gets blocked off. As the heater core always has coolant flowing through it (not like some other models) then this will always introduce some heat. If the flap AFTER the heater core isn't shut properly then some air will come through this route.

Initially I was really worried my AC evaporator was clogged - either internally (from oil/gas) or externally from leaves/debris. I've got no real way of checking the inside of the evaporator though. The foam elements of the air inlet often perish and some of this could have made its way into the AC system/vents. Likewise the vents also have 'seals' which could also be going bad. They might not seal properly or worse clog a flap/motor from moving.
I looked on the internet for some pics/videos of what the heater box looks like but didn't find much. Nobody seems to have documented removing one so I put that to the back of the plan queue. There is one video on YouTube of a chinese garage removing a heater box from an LHD A6, but its sped up and has irritating music. Alternatively some boxes are now for sale, but unless they have photos from all angles its hard to see much of relevance.



If you wanted to remove the heater core it might be possible to leave everything else in the car, but AC evaporator needs it all taking out and its a lot of work. Personally I hate taking interior panels out as they are more fragile and less forgiving.

I focussed on the flap motors instead. They showed no errors in VCDS. Having replaced one before I had a look to see that they were all doing what they should. On the N/S you can remove the glovebox to see them. Start the car, play around with the temperature and mix buttons and see them all moving. I did the same and disconnected the temperature flaps to see if they moved any further but there was no change. On the driver side its harder to get to. You need to remove the plastic scuttle under the steering wheel, then lots more bits to even see some flap motors. Mine all seemed ok.

The drain plug....
We should all know about the drain plug by now. Its been well documented that they clog, could cause evaporators/covers to fill with condensation and potentially icing up the evaporator. They also block and cause the footwell to be flooded. I decided to give my evaporator a really good clean and to do this I removed the drain piping, fan resistor and a small bung at the bottom of the heater box. First I filled the heater box with some HVAC foam cleaner. It starts coming out of every little crack and eventually the vents. Leaving this in for 20 minutes and then start the car and AC/heating on. Didn't make a difference. I've also got an inspection camera so popped that in too - nothing much to report and couldn't see any debris. I then tried my steam cleaner, fashioning a thin pipe outlet on the standard hose (made out of brake pipe). Cleaning it from both directions. The excess vapour came out the drain hole.

This didn't make any difference to the temperature but did make it smell nice!

The condenser:
I've just replaced the condenser on my other halfs Seat Leon TFSI and although her AC worked it wasn't mega cold. Her condenser was in a terrible state though, almost turning into dust. New condenser and a regas its lovely and cold. New condenser was only £60 too!.

I gave my condenser a little clean with some normal products, steam cleaner plus used the compressed air to get any leaves out. Seems pretty clean anyway. There's a few fins which are dented and could be straightened but nothing major.

Obviously RS tax means a condenser for ours would be atleast 5 times the cost, so should I replace mine even though it doesn't look that bad?
I found a condenser a few months back at a place called deutsche parts. Genuine OE Audi part 4B3260403H. It was £350. I decided to give it a miss.
Months later I thought I would be able to find one cheaper. The one from deustche parts was now sold (D'oh!)
Eurocarparts and Autodoc is normally my first port of call. ECP didn't even sell them.

Bugger.

Autodoc lists 2 different types of condensers for the RS6. One has outlets which are on pipes either side of the condenser (and are available for less than £200). Unfortunately my condenser didn't look like those..... it looks like the other one (like this https://www.autodoc.co.uk/denso/7059476 ) and none of them are in stock. I then spent about 2 weeks looking for other stockists. None available. Rang Audi. Nope. I had 3 glimmers of hope:
- a supplier on ebay who said his suppliers were showing them in stock. But didn't.
- a supplier online who had the exact part listed (and in stock) but then emailed to say in was on back order.
- from Amazon (?!?!!?) who listed an OE spec one from AKS DASIS in Germany in stock. Delivery of 4-6 weeks. Ordered and contacted them 6 weeks later only to be told they have no idea when it will be in stock.

There are a couple of places in the US who might have one. But they are listing them as $800-900 :shock:

I wasn't going to spend that much if mine *might* be ok. Probably cheaper to get mine re-cored somewhere. If anyone finds a genuine supplier - well done! Doesn't bode well if someone has a front shunt and needs a replacement. I did look at some other Audi models to see if there were any similar, or also fitting different pipes too. The condenser for a B7 S4 looks pretty similar and are available, but the outlets are inches away from where they need to be. Could be done maybe with some bending/adapters but there isn't much space to work with.

It would useful if anyone else could check what their condenser looks like. Perhaps later models had different connections with other pipes. Nwer models seem to also incorporate a receiver/dryer on the units too.

What else....

Restrictor/Orifice tube:
The RS6 uses an orifice tube to manage the 'how does it get cold?' bit. The compressor controls the flow of refrigerant (by turning on and off) and the orifice tube simply takes the high pressure refrigerant and lets a tiny bit through, the refrigerant expands and at a lower pressure turns to a super cold gas. This then goes into the evaporator which absorbs heat and you get nice cold air.
I didn't even know where the orifice tube was fitted (or whether my car had an expansion valve instead like some other cars). I ordered one anyway and then looked for it (they are only cheap). Under the coolant reservoir (which is under the scuttle panel) the AC tubes go across the engine bay to the heater inlet. One pipe is solid an the other one has a large union (23+mm). The orifice tube slots down one of these pipes.

NB: Other cars (like my Mrs Seat) have a fixed output compressor, and a expansion valve which controls the flow to the evaporator. Remember this if you order a replacement compressor.

I decided to throw caution to the wind and swap it my orifice tube. Local garage got all the old refrigerant out and I did the rest. You undo the pipe and the orifice tube needs to be fished out with some long nose pliers. Quite hard to pull out. Hmmm... it doesn't look that bad..... Gave it a bit of a clean and a few gritty bits came out the filter. Now, lets put the new one in. And it wouldn't go in. Scratching my head for a while. Looked at the diagrams. Try to replicate how the old one came out. Was the old one in backwards??????? No way. Surely not. I'm not 100% sure if it was or not but I'm 90% certain thats the way the old one came out. I put the new one in the proper way (it has a direction arrow on it - for flow towards the evaporator). Refilled with gas. Its cold!

Yipee!

Was that the problem all along? Was the orifice tube blocked or was it fitted backwards. I'll never really know. In theory if it was backwards then refrigerant would still flow through it. It has no moving parts and can flow in both directions.

Other things to note...

I also replaced the receiver/drier as this is recommended when doing significant work on HVAC systems. Only problem is I could find one that was correct. In the end I ordered and fitted one which has inlet/outlet straight opposite eachother, however the standard one is slightly offset. Spoke with Audi and they are no longer in stock. I did manage to fit it though with some bending of pipes. The connecters are the same size. Its pretty close to the headlamp though so don't want to change any bulbs soon.

I've since found one though (and ordered one). From autodoc they list ones for the early 1990's Audi V8! There's some here. I didn't look up the audi part number so there may be more available somewhere else. Audi genuine ones were a lot more expensive too.
https://www.autodoc.co.uk/car-parts/dry ... -2-quattro

My theory on why the NS air vents were always cooler - The AC gas enters the evaporator from the left side of the car i.e the passenger side. The dual climate splits the air after the evap/heater core. So if there's only enough refrigerant to cool down a little of the evaporator the NS would get it better. I think eventually that heat soak would go wider though. Since my regassing the difference isn't noticeable.

So, hopefully I've helped someone along their journey of self diagnosis.

Cheers
Chris
Last edited by Nobby on Wed Jul 20, 2022 5:02 pm, edited 1 time in total.
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Shoppinit
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Re: Air con - fixed just in time for the heatwave

Post by Shoppinit » Wed Jul 20, 2022 4:03 pm

Very nice write up. :thumbs: Will no doubt be extremely helpful for anyone trying to get their head around the voodoo that is AC.
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Capt Ric
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Re: Air con - fixed just in time for the heatwave

Post by Capt Ric » Wed Jul 20, 2022 8:05 pm

Chris, thanks for taking the time to write that up.
Well done.

steve2003rs6
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Re: Air con - fixed just in time for the heatwave

Post by steve2003rs6 » Sat Jul 30, 2022 1:59 pm

Very informative and a great write up.

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