A/C madness. Low pressure, sensor problem or just low on R134?

[NEO]

I have been reading up on related issues here but I thought that I should bounce this here and see what you guys think.

I will cut this story short and if you want the long story you can read up on Irry.com:

http://irry.com/en/the-cars/the-bathmobile/397-oil-change-and-ac-repair.html

http://irry.com/en/the-cars/the-bathmobile/398-the-ac-madness-continues.html

The short story is that I swapped a pipe, a hose and the compressor and got the system pressure tested and filled. And now when monitoring channel 52 and 53 on the OBD it tells me that the pressure is too low in the system. The symptom is that the compressor goes on and then goes off again in an endless cycle since it believes that the pressure it too low. When shortening the A/C compressor safety valve the compressor keeps running but there's not relly much cold to talk about. In the shop just after the system was filled up he measured 5.8 degrees Celsius in the center air vent but now it wont go down under 17.

As you all know the valve on the compressor is a bit hard for the workshops to fit their equipment on and the guys I turned to had the same problem. Eventually they managed to get a hose fastened but it wasn't a super tight fit and a "digital nose" used when looking for leaks detected gas where it connected to the valve. It didn't get better of that the seal in the hat for that valve in the compressor accidently pressed the pin in the valve for a good 30 minutes while I drove to my garage. The mechanic should have spotted this directly but for some reason he didn't and an unknown amount of gas leaked out. So these two things makes me draw the conclusion that the system isn't full. Hence that the warning I get in the OBD is correct and that the pressure is too low.

Anyone else have a few cents to spend on this? Could it be something else? Faulty sensor or something?

[johne]

From what you describe I think you've lost much of your R134a gas. You need to go and get your system refilled.

John

[A80Avant]

i need to change that pipe as well.

it sounds that indeed you have lost the refrigerant gas. I had a similar problem and when regassed, everything went back to normal.

by the way, when you tried to undo the hose from the collector, did you find that the alloy threads where corroded and needed the whole thing replacing?

[Casper...]

Hey NEO

I did a lot of reading on my self when I did my A/C (2 week ago) and from what I read on this forum, I did not read about a valve on the compresser (When talking the ABY /RS2) I assume that your refer to the low pressure valve ?

The only way to be sure is to mount the the gauges and measure the pressure that way you would now for sure If you have enough pressure in the system and take it from there.

mvh

Casper...

[veneto rs2]

I just had a problem with my A/C aswell.
After a deep check (lost gas three times) eventually the technician found with the UV lamp that my upper hose connected on the condenser was leaking.
Changed the pipe (it has a connection close to the gearbox near the clutch bell) and now it's working perfectly.

I can say that when our compressor start to cycling on/off on/off on/off and so on...
You are defenetely loosing gas somewhere.
If the system it's tight and no leaks our system keeps the compressor always on.
Sometimes the tachnicians are use to different systems on different cars/brands that are normally switching the compressors on and off and this can confuse them to the point that for them it's working ok...... it is not.
So keep in mind that the A/C compressor on our cars stays on until you switch off the A/C period.

While doing this I went trough (like NEO) on the FIND of the freaking leak issue.

One part that can be guilty and not easy to detect it's the condenser itself.
If you have a hole in there an the hole it's on the side between the condenser and the main radiator it's an absolute nightmare to detect it.
The gas and the special revealing yellowish/greenish oil gets on the fins of the condenser and there's no way you can see it if you don't take the condenser out.

If it's the condenser........ no need to say that you can source the part for not much more then 100/120 euros on the german bay.
Audi asks something ludicrous like 500/600 euros.....

It's not common (but ofcourse possible) on the other side to have a fault on the inside evaporator in cabin.
Better because in this case it's a dashboard out job......
The gas there it's on low pressure, and if oyu have a leak there the revealing oil detector could be seen underneath the car together with the condesing water coming out from the drain.


Hope this help and good luck!

Stefano

P.S.

Another sign of gas leaking it's a noisy (sort whirrring noise) from the compressor.
If the system it's not tight and you're loosing gas you'll have firstly noise from the compressor and then the on/off ciclyng.

[NEO]

Yep. That was it! We refilled it this morning and now it keeps the cold! WHen I drove home the lowest I measured was 2.3 degrees, brrrr! An hour after getting home I just got it slightly under 9 degrees though which made me nervous. But now, this evening, I got it to 4.8 in just a few minutes. =) I'm carefully optimistic and but I really really hope that it's all ok now. =)

From what you describe I think you've lost much of your R134a gas. You need to go and get your system refilled.

John

[NEO]

by the way, when you tried to undo the hose from the collector, did you find that the alloy threads where corroded and needed the whole thing replacing?

Hmm.. The collector? Do you mean the drier in the passenger front fender? You should always replace that if the system have been open for a fairly lengthy period and 11 years with a leak should count as that. So, I had already planned to replaced it and had a new one on shelf. I never managed to remove this end from the old pipe and sawed it off instead. I didn't manage to unscrew it with the drier on the ground either and I have been warned about the various A/C parts and that the threads usually corrode to smithereens.

[NEO]

HEy Casper

No not the low pressure valve. The low pressure valve is actually located under the glove compartment on the passenger side (on a LHD car). The compressor safety valve is located on the pipe on the condenser, right next to the green high pressure valve.

Hey NEO

I did a lot of reading on my self when I did my A/C (2 week ago) and from what I read on this forum, I did not read about a valve on the compresser (When talking the ABY /RS2) I assume that your refer to the low pressure valve ?

The only way to be sure is to mount the the gauges and measure the pressure that way you would now for sure If you have enough pressure in the system and take it from there.

mvh

Casper...

[NEO]

I can say that when our compressor start to cycling on/off on/off on/off and so on...
You are defenetely loosing gas somewhere.
If the system it's tight and no leaks our system keeps the compressor always on.
Sometimes the tachnicians are use to different systems on different cars/brands that are normally switching the compressors on and off and this can confuse them to the point that for them it's working ok...... it is not.
So keep in mind that the A/C compressor on our cars stays on until you switch off the A/C period.

I don't want to be a besserwisser but that's a truth with modification. When doing a kickdown the compressor will shut itself of for 12 seconds. Also when it's sub zero outside it wont come on or will turn it self off. All this can be monitored on channel 52 in the OBD.

While doing this I went trough (like NEO) on the FIND of the freaking leak issue.

One part that can be guilty and not easy to detect it's the condenser itself.
If you have a hole in there an the hole it's on the side between the condenser and the main radiator it's an absolute nightmare to detect it.
The gas and the special revealing yellowish/greenish oil gets on the fins of the condenser and there's no way you can see it if you don't take the condenser out.

If it's the condenser........ no need to say that you can source the part for not much more then 100/120 euros on the german bay.
Audi asks something ludicrous like 500/600 euros.....

It's not common (but ofcourse possible) on the other side to have a fault on the inside evaporator in cabin.
Better because in this case it's a dashboard out job......
The gas there it's on low pressure, and if oyu have a leak there the revealing oil detector could be seen underneath the car together with the condesing water coming out from the drain.


Hope this help and good luck!

Stefano

P.S.

Another sign of gas leaking it's a noisy (sort whirrring noise) from the compressor.
If the system it's not tight and you're loosing gas you'll have firstly noise from the compressor and then the on/off ciclyng.

Mmm... The condenser is probably the only thing left in my system that could leak, unless one of the o-rings die on me now when there's pressure in the system. Luckily I'm one of those nutcases that buy stuffs just for the sake of buying them so I have a condenser from an RS2 on shelf. It was from that kit I took one of the hoses and the compressor I mounted on the car this time around.

[veneto rs2]

Sorry about the incorrect infos.
Here in Italy with 33/35 degrees I did'nt thought about low temperatures nor the wot switching off thing.
While we're sharpening toothpicks I must for history records correct you aswell thoug.
The compressor doesn't start with temps below 5 degrees Celsius and not below zero.
And the wot does not switchoff the compressor for 12 secs but it kicks back in as soon as the throttle switch inside the potentiometer hits back the full close position you don't need the VAG to test it you can use your bare hand like once upon a time.
Now to correct myself I would say that:
With a temperature of more then 5 degrees and with car on idle or without a fast wot the A/C compressor in the S2/RS2 stays on until you switch off the A/C or the motor.

Stefano

P.S.
Can I advise to Check that the condenser in your shelf it's sealed or your new drier will be quickly affected.

[A80Avant]

i see
then a drier needs to be ordered as well then...

[johne]

While we're sharpening toothpicks I must for history records correct you aswell thoug.

Now to correct myself I would say that:
With a temperature of more then 5 degrees and with car on idle or without a fast wot the A/C compressor in the S2/RS2 stays on until you switch off the A/C or the motor.

The low pressure switch is the primary control for turning the compressor on and off. Yes, WOT, high coolant temperature and ambient outside temperature below 3 degrees C will all turn the compressor off but they are just secondary protection mechanisms, the low pressure switch controls how cool the system gets switching the compressor off before the system freezes up.

If it's hot outside and the engine speed is low or close to idle the system will never get cold enough for the low pressure switch to drop out so that's why it appears that the compressor is on all the time.

If you're already low on gas the pressure will drop quickly and the compressor drops out. What little gas there is in soon warms up, pressure increases and the compressor kicks back in hence causing the short cycling described in this thread.

In a normal healthy system the compressor will stay on far more than it is off - but not necessarily on all the time.

John