2005 Colorado HVAC issues

[Randy Groover]

I have a 2005 Colorado with an HVAC issue that my Chevy dealer can't seem to solve. After approximately 15 to 20 minutes of driving the air flow from the AC vents begins to diminish to barely nothing. The fan is still blowing full blast, just nothing is coming out of the vents. If I turn the AC off and allow fresh air to come through, after about 2 minutes the air flow returns to normal. Then I can turn the AC back on and the process begins again. My dealer has replaced a connector and a resistor and said it was fixed. The problem recurred so I took it back. This time they replaced the evaporator and compressor, which was quite expensive, only to have the issue return. I am scheduled to take it back Monday for another crack at it. Please help if you can.