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witt0018, Technician
Category: Audi
Satisfied Customers: 1322
Experience:  NVQ 3, Modern Apprenticeship, MOT tester, 14 years experience working on all makes and models
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Audi Q7 Premium: I have a 2008 Audi Q7 4.2.A/C in the car

Customer Question

I have a 2008 Audi Q7 4.2.
A/C in the car has never been what I believe it should be. Today was the warmest day of the year so far, 92F, and I couldn't get any cooler than about 65F at the vents on max cool in recirc.
I do a lot of work on cars, and have done work on A/C systems as well. I have hooked up the manifold gauge set and have pressures of about 53 psig on the low side and about 225 - 240 psig on the high side.
I was under under the impression that the low side should be more towards 30 psig, but the high side seems in spec. Thinking it may have been overcharged at some point, I removed some of the charge, the high side lowered a little, but the low side stays the same, and cooling did not increase, but got a little worse.
What I'm looking for is for someone who has experience with newer Audi A/C systems to pinpoint the issue...
Submitted: 2 years ago.
Category: Audi
Expert:  witt0018 replied 2 years ago.
Welcome to just answer
The air conditioning on your car has to have a measured amount of R134a refrigerant in the system.
Your car should contain 700g of gas with a tolerance of + 50g of PAG oil
If you have rear air conditioning as well then you should have 1050g of refrigerant and 50g of PAG oil.
The original pressures you have on the low side seem correct, but the high side a little low, so I'm sure that the gas has just depleted which is normal, the refrigerant should ideally be removed every 2 years and replaced.
Hope this helps, if you need more info, please let me know.
Customer: replied 2 years ago.

I'm sorry, I'm aware of this information. It's on a label under the hood.

According to everything I've read for r134a...

These are only approximate values, but, the low side should be around 27 psig to achieve just above freezing temps in the evaporator. The high side should be approx. 2.1 - 2.5 times outside ambient temp.

So...that gives me an acceptable high side range of around 193 - 230 psig.

If anything I'd go to say that the only thing that seems abnormal is the low side pressure...which is why I am seeking advice from an Audi specific A/C technician...thinking that maybe this particular Audi has an abnormal expansion valve setup or something.

Thank you for your reply, but if you are unsure of the specifics of this vehicle, please let me know.

And yes, this vehicle does have rear A/C as well.