AC not cooling if outside temperature is above 95F / 35 C

[Jensfl]

Hello. I’m having issues lately with the AC on my 2008 Audi A4 2.0T.

I have been experiencing issues with my AC lately (and living in south Florida, a proper functioning AC is definitely needed :).
The AC seems to work somewhat ok (blowing 42-44 F) in the early morning, or late evenings or at night, when outside temperatures are below 90F. But when the sun is blazing and outside temperatures are nearing or above 95F (35C), the AC blows 50F for a short period and then rises quickly to blowing the outside temperature.
I also noticed that the left (driver side) vent blows the coldest, then each vent going to the right blows warmer. For example: at 90F outside temperature early in the morning, the left vent (driver side) blows 44F, left center console vent blows 52F, right center com ole vent blows 60F and right vent (passenger side) blows 74F. That seems like a big difference.
I already checked the heater core air mixing vent door (or whatever the correct name for this thing is), and it closes all the way. Also, all vents blow the same amount of air, just not the same temperature.

Notes: a new compressor, condenser, dryer, orifice tube, etc. was installed over a year ago, when the compressor died. The correct amount of Freon was added to the system at that time (by weight).

I hooked up my gauges (in the evening at 88F) and it showed the following: low side 110 and high side 110 when engine was off, then after running the AC on high for 10 minutes it showed: low side 20 and high side 150.

Does anyone have any ideas?

[wding2000]

Are those (Lo 20 and Hi 150) in psi? I saw different tables calling different pressures. One chat shows:
at 88F, Lo 28-43 or 32-47 (depending on humidity); Hi 146-205 or 160-213.
But Lo 20 does seem low in any tables.

Just for reference: mine is running Lo 30 Hi 125 at 69F; and Hi side can go up to 250 psi at higher temp (forgot exactly what temp).

[Jensfl]

Hi. Sorry, yes the measurements are in psi.

I first though it might be low on Freon, but then I doubt the AC would be able to blow 44F when it below 90 F.
I wonder if there is a sensor or something that is faulty and acts up when it’s 95F or above in ambient air temperature.
Scratching my head.....

[wding2000]

If Hi side more or less normal, but Lo side low, could be blockage at orifice? but you said you had a new one. So ... not sure. Best to look VCDS, compare between 44F and 90F (such as ambient air temp, pressure, etc).

A/C can be very complicated to diagnose. I am glad my issue was just hi-pressure sensor - still took me some time and work to finally narrow it down.

[RDA990]

Might not be your issue but have you checked if both fans are running without an issue?

Turn AC on Lo and visually check the radiator fans to verify they are BOTH spinning.

[Kevin C]

I would get the charge rechecked. I think you lost about 1/2 a can (6 oz) of freon.

[Jensfl]

Might not be your issue but have you checked if both fans are running without an issue?

Turn AC on Lo and visually check the radiator fans to verify they are BOTH spinning.

Hi, and thanks for the reply. Yes, both fans are spinning. I remember now that the AC fan and the fan control module were replaced when the compressor was replaced a year ago, because the fan only worked on low speed.

[Jensfl]

I would get the charge rechecked. I think you lost about 1/2 a can (6 oz) of freon.

Hi and thanks for the reply. Do you think this because of the gauge reading or the issue in general? I initially suspected low Freon as well, but then would the AC be able to consistently blow 44F at the left vent at 90F outside temperature ? This is what made me scratch my head. In previous cars when the Freon was low, it wasn’t able to get cold at all. Any thoughts would be appreciated, before I get the system recharged. Thanks a million.

[Kevin C]

Sounds like what I had on my B6.... same basic system.

https://www.audizine.com/forum/showt...ifferent-temps