I have 99 Chevy Silverado Z71 that the a/c works great in, but only drains the condensation out while the a/c is on. If I drive with the a/c for a considerable time for condensation to build, park and and shut the truck off , it may drip a little. But, if I turn the key to run without starting the truck and turn on the fan it will gush a lot of water out. A friend of mine has an '04 Silverado that gushes out water after he shuts his truck down. I tried running a stiff zip tie up the drain, but it didn't seem clogged. Any suggestions on what I should try next or is it normal? Thanks.