Help Please A4 B8 Aircon Pressure Switch Replacement

JamesRyder

Registered User
Hi all,

I had my aircon regassed recently, and the garage informed me that the aircon pressure switch is faulty and needs replacing. I've read conflicting reports on whether you need to regas the system after swapping the switch out. I've just called a garage and they informed me that they will need to do a regas, and the total will be around £160, which is pretty reasonable all told. I did mention that I've read that it won't need regassing though, but the receptionist told me that 'it does as they need to break into the system'. I appreciate that you can do this job yourself, but my car DIY skills are pretty rubbish if I'm honest.

I also got a quote from Audi, which was £287, inclusive of regassing if required. Seems like Audi don't even know if a regas is required or not.

Could somebody clarify this for me please? I don't really want to pay for another regas if it's not required.

Thanks :)
 

V6_Man

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Staff member
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VCDS Map User
Hi all,

I had my aircon regassed recently, and the garage informed me that the aircon pressure switch is faulty and needs replacing. I've read conflicting reports on whether you need to regas the system after swapping the switch out. I've just called a garage and they informed me that they will need to do a regas, and the total will be around £160, which is pretty reasonable all told. I did mention that I've read that it won't need regassing though, but the receptionist told me that 'it does as they need to break into the system'. I appreciate that you can do this job yourself, but my car DIY skills are pretty rubbish if I'm honest.

I also got a quote from Audi, which was £287, inclusive of regassing if required. Seems like Audi don't even know if a regas is required or not.

Could somebody clarify this for me please? I don't really want to pay for another regas if it's not required.

Thanks :)

It would need regassing after the pressure switch replacement. I had it recently replaced on my B8.5 S4 however, it cost me £110-ish including parts from APS Brackley. £162 seems slightly excessive given the cost of the parts and regassing.

Link below to my thread showing part numbers etc.

https://www.audi-sport.net/xf/threads/b8-5-s4-aircon-not-blowing-cold-air-emoji51.387674/
 

JamesRyder

Registered User
Thanks for your quick response, Tashfeen. In that case, I'll shop around for a better quote. Maybe I'll rephrase my statement then, to "£162 is reasonable... compared to the ridiculous quote from Audi". Hopefully I can bring that price down a bit though.

Thanks again :)
 

V6_Man

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Thanks for your quick response, Tashfeen. In that case, I'll shop around for a better quote. Maybe I'll rephrase my statement then, to "£162 is reasonable... compared to the ridiculous quote from Audi". Hopefully I can bring that price down a bit though.

Thanks again :)

Not a problem bud. Also, it might be that your garage is charging you for the diagnostics and if so the price does seem reasonable. APS didn't charge me for diagnostics and said it was 'free', which I saw as a kind gesture!
 

JamesRyder

Registered User
Not a problem bud. Also, it might be that your garage is charging you for the diagnostics and if so the price does seem reasonable. APS didn't charge me for diagnostics and said it was 'free', which I saw as a kind gesture!
Yeah, I guess that would make sense with the diagnostics. The garage that actually did the regassing told me the switch is fudged, but I'm not sure if they did diagnostics or not. They quoted me £141 to replace the switch (£70 labour, £70 for the part, no mention of regassing). They just told me it's a common fault so they might be assuming it's the switch.

I've just rang another garage that has a decent local reputation, and he wouldn't give me a quote, as he said that he needs to inspect it. When I said AC pressure switch, he said 'Is it an Audi'. He said that it could be something else, like the AC compressor unit, and to swing by next week. He was a bit grumpy, but I often find those types of mechanics are the honest ones.
 

V6_Man

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Yeah, I guess that would make sense with the diagnostics. The garage that actually did the regassing told me the switch is fudged, but I'm not sure if they did diagnostics or not. They quoted me £141 to replace the switch (£70 labour, £70 for the part, no mention of regassing). They just told me it's a common fault so they might be assuming it's the switch.

I've just rang another garage that has a decent local reputation, and he wouldn't give me a quote, as he said that he needs to inspect it. When I said AC pressure switch, he said 'Is it an Audi'. He said that it could be something else, like the AC compressor unit, and to swing by next week. He was a bit grumpy, but I often find those types of mechanics are the honest ones.

I kind of agree with the 2nd garage as it could be the compressor however, it is usually the switch which is the culprit 9/10 times. Would've been easier if you had VCDS to scan and find out.

The first garage should've checked for the leaks and run the scan as it is highly unlikely the problem appeared after regassing. My personal view is you should push them and ask to do the change with no charge for the diagnostics.
 

rum4mo

Registered User
The facts are, these pressure sensors - they are not switches, tend to leak and so normally when you change a pressure sensor you have only covered half of the job, ie stopped the leak, now the system charge needs sorting out.

Also, if your pressure sensor is really faulty and not leaking, then all you need to get done is the old pressure sensor unscrewed and the new pressure sensor fitted, nothing else, there is a Schrader valve below that pressure sensor so it will "hiss" very slightly when you remove the old sensor - don't be put off, just quickly complete the removal, same for the fitting of the new sensor, also don't buy discontinued old stock that has been disposed of by VW Group, buy the latest version as they do tend to, like quite a lot of VW Group parts, revise/sort designs out over time. It can be found at the side of the radiator area under the plastic water deflector.
 

JamesRyder

Registered User
Thank you both for your feedback. rum4mo, that probably explains where I've read two sides of the story on these sensors with not having to refill (faulty sensor but not leaking), and having to refill (leaking sensor). I know the garage that did the regassing has diagnostic tools, and their reputation is pretty good for a general garage, so I'm hoping they did diagnose the fault before telling me what the problem is and quoting me for it. The thing that puzzles me is that I had a service done with Audi about 2 months ago, and the aircon wasn't working then. It states on the invoice that they checked the system memory for faults, but they didn't report anything.

Anyway, thanks again for your help, rum4mo and Tashfeen. You've given me some good knowledge to go forward with this. I really need to buy myself a scanner so that I don't have to rely on garages.
 

johnny161171

Member
VCDS Map User
So out of curiosity when you press the ac button in the car does the switch stay illuminated or does it switch off straight away
 

JamesRyder

Registered User
So out of curiosity when you press the ac button in the car does the switch stay illuminated or does it switch off straight away
Hi johnny. Thanks for your message. The ac button stays illuminated and everything seems to be working properly. I can change the fan speeds and change the temps and the ac light stays on. It's just the air doesn't get very cold.
 

Owyn

Registered User
Mine died a couple of years ago, it's a little block at the side of the radiator with an electrical socket on it (my memory could be hazy so it may be somewhere else).
I bought a new one, screwed the old one off and screwed a new one on.
As has been said, it has a schraeder valve which isolates it automatically when you screw it off.
Mine was goosed but the seal was fine, if the seals knackered then you can just change the o ring.
Mine showed a fault on my obdeleven so was easy to diagnose.
 

JamesRyder

Registered User
Mine died a couple of years ago, it's a little block at the side of the radiator with an electrical socket on it (my memory could be hazy so it may be somewhere else).
I bought a new one, screwed the old one off and screwed a new one on.
As has been said, it has a schraeder valve which isolates it automatically when you screw it off.
Mine was goosed but the seal was fine, if the seals knackered then you can just change the o ring.
Mine showed a fault on my obdeleven so was easy to diagnose.
Thanks for your input Owyn. I'm almost tempted to try to fix this myself to save on the £70 garage bill. I've just found a link from some guy that provides photos and instructions for replacing it on an A5. I presume it's in the same place, as you and rum4mo mentioned, and the guy uses the same part number (4H0 959 126 B) that he bought from Audi. I just need to buy or borrow a crowfoot spanner.

Looks like you can get the B variant for £26.50 from eBay:
https://www.ebay.co.uk/itm/GENUINE-...470979&hash=item2cea46985b:g:kWkAAOSwBAxc0HyD

Instructions for replacing:
https://www.a5oc.com/forums/audi-a5-s5-tech/145265-air-con-pressure-sensor.html

G395 sensor.jpg
 
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Owyn

Registered User
It is similar to this but the condenser looks different on mine.
I didn't use a crows foot spanner, I can't remember what I did use but you can probably get a normal spanner in, certainly worth scoping it out to see what you can do, you just have to get the plastic slam panel cover off.

As for DIY, it's way easier than a spark plug so if you can do that you should defo do it, it took me about 10 minutes I think.

It is quite a pricey part though, I'd make certain that is the problem before replacing it. My recent experience of air con specialists is that they are few and far between and if it's beyond what the machine can do they are stumped and then suggest spraying cash at it.
 

JamesRyder

Registered User
It is similar to this but the condenser looks different on mine.
I didn't use a crows foot spanner, I can't remember what I did use but you can probably get a normal spanner in, certainly worth scoping it out to see what you can do, you just have to get the plastic slam panel cover off.

As for DIY, it's way easier than a spark plug so if you can do that you should defo do it, it took me about 10 minutes I think.

It is quite a pricey part though, I'd make certain that is the problem before replacing it. My recent experience of air con specialists is that they are few and far between and if it's beyond what the machine can do they are stumped and then suggest spraying cash at it.
Thanks Owyn. I might get a scanner and confirm if it comes up with the sensor fault first in that case, as I'll no doubt need a scanner in future. Although I've found the part on eBay for £26.50, which looks genuine (although I guess you never know with eBay).
https://www.ebay.co.uk/itm/GENUINE-...470979&hash=item2cea46985b:g:kWkAAOSwBAxc0HyD

I'll take a look at the car at lunchtime to see what's what. It would be good not to buy a crows foot spanner. I would definitely like to avoid an expensive garage bill right now. They said they'll probably have to take the bumper off, just to make up the £70 hour's labour, I presume :)
 

rum4mo

Registered User
Please resist buying an older version via ebay, as I hopefully said earlier, these parts on ebay from a 3rd party are normally discontinued/revised/replaced versions and they have been revised for a very good reason, due to the cost and cost saving if buying via ebay, I'd be planning on buying the latest version from a supplier of Audi parts and play safe by buying a new O-ring seal, then when replacing the sensor and seal rub any oily deposits that were on the original seal onto the new seal to help lubricate it.

Some on line VW Group dealerships do give genuine discounts, unlike some others that claim to!

Spanner, nothing fancy needed I'd reckon and these items are not screwed in very tightly, plus sometimes VW Group makes the "size" of the new version bigger/smaller than the original, well at least their suppliers do, so buying a single crows foot spanner might not work.

I too am surprised that the system works but only cools slightly if it is only a pressure sensor issue, okay the pressure scaling might be out a bit but I'd expect the system to shut down or not start if that sensor was faulty, maybe the "faulty" output is a true reflection on what is happening within the system, ie not root cause. Take very great care when buying a scan tool as not all scan tools can communicate with all these cars smart controllers.
 

JamesRyder

Registered User
Please resist buying an older version via ebay, as I hopefully said earlier, these parts on ebay from a 3rd party are normally discontinued/revised/replaced versions and they have been revised for a very good reason, due to the cost and cost saving if buying via ebay, I'd be planning on buying the latest version from a supplier of Audi parts and play safe by buying a new O-ring seal, then when replacing the sensor and seal rub any oily deposits that were on the original seal onto the new seal to help lubricate it.

Some on line VW Group dealerships do give genuine discounts, unlike some others that claim to!

Spanner, nothing fancy needed I'd reckon and these items are not screwed in very tightly, plus sometimes VW Group makes the "size" of the new version bigger/smaller than the original, well at least their suppliers do, so buying a single crows foot spanner might not work.

I too am surprised that the system works but only cools slightly if it is only a pressure sensor issue, okay the pressure scaling might be out a bit but I'd expect the system to shut down or not start if that sensor was faulty, maybe the "faulty" output is a true reflection on what is happening within the system, ie not root cause. Take very great care when buying a scan tool as not all scan tools can communicate with all these cars smart controllers.
Ah sorry. You did mention about avoiding third-party sellers on eBay. None of the other parts I looked at have the part number printed on the part, but the one I linked to does (pic below), so I presumed it was a genuine part. Lesson learned - no more mention of buying from eBay. I do my girlfriend's nut in with trying to constantly save money. And thanks for the advice on scanners. I'll do some thorough research first. After this discussion, I don't know if I trust the garage that did the regassing, and then told me the sensor needs replacing. The garage that told me he needs to see the car first is probably a better bet for diagnosing the problem if I decide not to go down the DIY route for this.

Thanks for your help everyone :)

Sensor.jpg
 

rum4mo

Registered User
I’m not knocking all the stuff that passes through eBay, some NOS gets auctioned off by VW Group due to packaging design change or dealerships collapsing, but some things like these sensors do get auctioned off as VW Group have revised the part for good reasons and no proper VW Group dealer will just flush them through the customers.

Some stuff is genuine and same as you would buy from a VW Group dealership parts dept, just slightly cheaper or dearer after adding on p&p.

I have been known to buy via eBay - many times.
 

JamesRyder

Registered User
I’m not knocking all the stuff that passes through eBay, some NOS gets auctioned off by VW Group due to packaging design change or dealerships collapsing, but some things like these sensors do get auctioned off as VW Group have revised the part for good reasons and no proper VW Group dealer will just flush them through the customers.

Some stuff is genuine and same as you would buy from a VW Group dealership parts dept, just slightly cheaper or dearer after adding on p&p.

I have been known to buy via eBay - many times.
Thanks for this information. Based on your sound advice, I'll definitely be avoiding eBay for parts that have revisions, and go through the official channels instead. You live and learn, and these forums are a godsend for newbies like myself :)
 

johnny161171

Member
VCDS Map User
You could take it down to Halfords get them to check if there’s any gas in the system by just putting a gauge on.
Its a free check.
My local Audi dealer used to re gas twice so they drain the system re gas drain and re gas again.
Bare in mind gas can lose its effectiveness over time so did the garage in question actually do a proper re gas.
I’ve never known a faulty sensor what I mean is the switch in the car you press it and normally would go off straight away if the sensor is faulty in my experience if you go down the route of fitting a new sensor make you get a new o ring with it
 

JamesRyder

Registered User
You could take it down to Halfords get them to check if there’s any gas in the system by just putting a gauge on.
Its a free check.
My local Audi dealer used to re gas twice so they drain the system re gas drain and re gas again.
Bare in mind gas can lose its effectiveness over time so did the garage in question actually do a proper re gas.
I’ve never known a faulty sensor what I mean is the switch in the car you press it and normally would go off straight away if the sensor is faulty in my experience if you go down the route of fitting a new sensor make you get a new o ring with it
That might be a good idea to check if they did regas it. This is the same company, but a different branch, that tried to quote me 600 for a water pump on my BMW when it broke down, just for the part. After telling them I can get it online for 300, my bill magically reduced by... 300. They have a good rep usually but this was a special deal they were offering for a regas, hence why I used them again. I guess there's a chance they're pulling a fast one. Although I did catch the end of it and they had a blue tube attached to the engine. I presume that was them regassing. If a faulty sensor is supposed to disable the AC button then checking it's got gas in it might be a good first step to rule that out.

Thanks for the advice :)
 

JamesRyder

Registered User
You could take it down to Halfords get them to check if there’s any gas in the system by just putting a gauge on.
Its a free check.
My local Audi dealer used to re gas twice so they drain the system re gas drain and re gas again.
Bare in mind gas can lose its effectiveness over time so did the garage in question actually do a proper re gas.
I’ve never known a faulty sensor what I mean is the switch in the car you press it and normally would go off straight away if the sensor is faulty in my experience if you go down the route of fitting a new sensor make you get a new o ring with it
Booked in for tomorrow. Thanks. If I find out there's no gas in it... :)
 

rum4mo

Registered User
You could take it down to Halfords get them to check if there’s any gas in the system by just putting a gauge on.
Its a free check.
My local Audi dealer used to re gas twice so they drain the system re gas drain and re gas again.
Bare in mind gas can lose its effectiveness over time so did the garage in question actually do a proper re gas.
I’ve never known a faulty sensor what I mean is the switch in the car you press it and normally would go off straight away if the sensor is faulty in my experience if you go down the route of fitting a new sensor make you get a new o ring with it

Not true, R134A is R134A nothing alters in it, its properties are only at risk from someone adding in some other or contaminated R134A. If the system has been opened up, then a new drier is needed, other than that these systems if kept closed and topped up with R134A and a spot of PAG oil, should run and run, not like large stationary systems where an electric motor is immersed in the R134A etc and any overheating or burning can form acids in the oil, so gas recovery and oil changes with testing and if necessary scrubbing out, is needed.

Edit:- there are some exceptions to this, but R134A is not an exception as some gasses used or used to be used are blends and one part of the blend can leak out quicker than the other, so the gas stops be optimal for that purpose.
 
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Booboo

Registered User
I have the A/C button not staying on on my 2014 A4. I had a new condenser and virgin regas last year too. So I'm thinking of changing this sensor. Did any of you fit a new O ring with it as I notice they don't come with one.
 

rum4mo

Registered User
I have the A/C button not staying on on my 2014 A4. I had a new condenser and virgin regas last year too. So I'm thinking of changing this sensor. Did any of you fit a new O ring with it as I notice they don't come with one.

Always buy and use new O-rings.
 

Booboo

Registered User
Just a little gob smacked they don't come with them and some places want near on five quid for one!

Ahhh I've just got one the exact proper size O ring off a tap flexi hose I had spare, 7.6mm x 1.8mm
 
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rum4mo

Registered User
Just a little gob smacked they don't come with them and some places want near on five quid for one!

Ahhh I've just got one the exact proper size O ring off a tap flexi hose I had spare, 7.6mm x 1.8mm

What material is that used O-ring made of, F gases are nasty stuff so need specific suitable O-ring materials for a few quid, I'd not be wasting my time guessing on suitability for use at this point.
 

rum4mo

Registered User
With the back ground to your car's HVAC system, I would think that the R134A has mainly escaped due to leaks, what you may have measured with the engine off is the fridge gas standing pressure, as soon as the compressor is asked to provide chilling, it will drag that pressure down and so disable the chilling and that will lead to the logged fault that you have found.
 

Booboo

Registered User
I did the test with the engine running. I'm hoping the system is ok I had a full system vac and new condenser last year. :shrug:
 

Booboo

Registered User
New rev B type sensor fitted. Still the same. I thought it may be as there was no pressure release "pist" sound when I removed the other one
 

Booboo

Registered User
Aircon service guy can't find a leak, he's been all over it with his UV lamp. He thinks it must have been the pressure switch I changed. He's pressure tested it and it hasn't dropped at all so He's regassng it now
 

rum4mo

Registered User
Only problem that I have with that is, there should/would have been evidence of system oil (mist) escaping around that previous pressure sensor, if it was dry and no sign of any oil deposits, then I would not think that your previous pressure sensor would have been the source of that leakage.

Some leaks, the easy and obvious ones will leak when the system is not running and a bit more when it is being used as the pressure at some sections of the system will be higher than when at rest. Other nasty leaks tend to get called "running" leaks and as the name implies, they might only be evident when the system is running - time will tell.
 
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