This is weird... For some reason, when I'm using A/C, the vents will randomly shut off. Sometimes it takes 20-30 minutes, sometimes 10 minutes, etc. The blower motor is still running and A/C compressor is on, but for some reason air won't come out of the vents after a while of driving. When I have the A/C OFF, with just outside air coming in, the vents work perfectly. I have lubed up the actuator, and made sure it is still working. Anybody have a clue as to what's happening with this? To get the vents to start blowing again, I have to flip around with the switch and then it will start blowing again. I should mention it does NOT default to defrost when this happens. I am at a loss of what could be the issue. Hopefully that all made sense.. Edit: truck is a 1997 Chevy K1500.