I have a 2000 Chevrolet Venture. It has front and rear A/C. Front AC works good, but when I turn on the rear fan, it doesn't always come on. Sometimes I have to leave it on, until it decides to come on all by itself. What can be causing this? Is it possibly an issue with the fan switch, or is it more complicated? I also notice that when the rear fan starts working, the air coming outside the front driver side vents gets cooler.

It could be a poor contact at the switch but more likely an intermittent open within the blower motor itself. Best is to check for battery power right at that blower connector when the fan is switched to ON. If you have power there, you will likely need the blower motor. If no power, that will need traced back to the fault.