Sounds like Rattle snake in car when Accelerating with AC on

I have a 2012 GLI with the 2.0TSI and last summer I started to hear this rattling/hissing noise while accelerating with the AC on. I was going to bring it to the dealer, but after some reasoning with myself, I said " it's probably the sound of the refrigerant entering the evaporator at higher pressure while accelerating"

Ive been going back and forth with myself on whether there's a problem or not, but I'm starting to think that there is a problem, here's why:

-power is way down. This is expected with the AC on, but when I first bought the car in 2015, I was amazed at the imperceptible loss of power with the AC on. You could always tell the AC was on in vehicles I had prior, but that wasn't the case with the VW until last summer. The DSG also does not up/down shift as smooth as it would with the AC off

-fuel economy is down ~30%. Again, a loss in fuel Econ is expected but on a route where I see 32MPG w/o AC, I'll only see 23MPG with AC running on same route.

This problem only seems to be apparent when the temp is 80+, and every thing is normal if I'm running the defogger on a cool night. I know head pressures rise with the temperature, but wouldn't the variable displacement compressor compensate for this?

All of this aside, the AC blows cold, and seems to be working properly in that regard.

Any of you guys deal with a problem like this?

How many miles are on it? Could it be carbon buildup? Maybe the intake manifold will need to be replaced soon? Really just thinking off the top of my head

If the noise is only present when the AC compressor is on, then your issue is with the AC system (more than likely the compressor). Only thing I can think of that would affect performance, is if the compressor is now seized.

GreyGti1990 said:

How many miles are on it? Could it be carbon buildup? Maybe the intake manifold will need to be replaced soon? Really just thinking off the top of my head

Click to expand...

I have 72K miles on the clock, and while I believe I'll have to clean carbon soon, the car runs perfect when the AC is not running.

Jaber said:

If the noise is only present when the AC compressor is on, then your issue is with the AC system (more than likely the compressor). Only thing I can think of that would affect performance, is if the compressor is now seized.

Click to expand...

the compressors in these things are interesting, to say the least. I remember searching google "AC compressor spinning while AC off" and found out that this is a variable displacement compressor, and it doesn't need a clutch.

I think whatever controls the compressor displacement is bad, but what is it? a switch?

WG flutter possible?