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? I was researching the issue and came across this "“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”…Could that be the issue?

your ac evaporator may be freezing up. there is either a pressure switch or a temperature sensor that shuts off the compressor before the evaporator reaches 32*F, so the condensation water won’t build up and block air flow. or the compressor relay may be sticking on. most likely, cheapest and easiest is the relay. i don’t know what a “vaporizer cap” is.