My A/C works really well, when it decides to kick in. Sometimes when I start my truck and turn the A/C on it blows hot air, so I have to turn the truck off and restart it and most of the time it will work just fine.

I had this problem with my '97 Dak back in the day and never got around to getting it fixed. What could this be? And is there a cheap/free way of fixing it?