A/C stops blowing and makes whistling noise on highway?

I am having trouble with my Chevrolet Aveo 2009 A/C. After driving for a while on the highway, the A/C stops blowing much air at low fan and when I increase the fan speed, it blows more air while making a whistling noise but not as much air as it usually does on that same fan speed. The noise starts going away after a while and it blows as much air as it should.
I noticed that it happens more when I keep accelerating every now and then on the highway. It does not happen as much when I am driving on a constant speed. I took it to the dealership and they said the filter was dirty and they found a leak on the vaporizer cap, fixed those but nothing changed!
Has anyone experienced a similar issue with their A/C? What might be the cause? Thanks :confused::confused:

Sounds like a vacuum line.. You tube has a few videos on how to repair you ac system. "Ericthecarguy" has multiple videos on car ac. hope this helps

I was researching online and I found the following "TPS (throttle position sensor) gives the WOT (wide open throttle) signal to the PCM to momentarily cut off power to the A/C clutch which disengages the A/C" -
See more at: http://community.cartalk.com/discussion/2128457/ac-cuts-out-when-accelerating#sthash.LzCOIv8e.dpuf"

Could this be the issue?

Its probably the above. Ac cuts out for more powahh