My AC freezes up occasionally, mostly in slower traffic but sometimes on hiway. Usually when blower fan is set to slower speed. If i turn up the fan speed I can hear the fan trying to push air, but next to nothing comes out of the vents. If i leave the fan going and defeat the AC, it will get back to normal blower flow in a few minutes, then the cold air warms up to ambient- I'm guessing there's an ice dam building on the heat exchanger that melts away after the AC is turned off. When I engage the AC again it will repeat the problem in 15 - 20 minutes. I get good condensate drainage, It continues to drip even after the ice dam builds. Is there a freeze-up sensor somewhere in the enclosure which I can check? Thanks for the help.