Need help on Air Condition Refrigerant (ran out on both cars!?)

So my bro told me that my corolla's a/c is not working. I'm assuming that I need to refill the refrigerant.
How often does it need to be recharged? I'm asking because my corolla hasn't reached 90,000 mile yet.
Is there a corolla DIY on air condition refrigerant refill?

Also this really sucks because my van ran out of a/c refrigerant as well. The thing is that my dad brought it(the Chevy Van) into a shop and they charged $90 to get it recharged etc. Everything worked fine, until the next morning, turns out the a/c wasn't working again. So i brought it back to the shop and told them that the a/c is refrigerant is probably leaking. They recharge it again, look around for leaks and they can't find any leaks. and once again the a/c is not working because it's probably leaking somewhere. I am trying to figure out what to do, the guy at the shop keeps saying it's this a/c pump? I'm not sure if he's correct. My other friend told me that I need to get a Dye and fill it into the a/c pipe to see where it is leaking, I'm not sure how to do this either... I have a feeling this won't be a cheap fix either. My van is a 97 Chevy Venture and it only has 93,000 miles on it. Engine is still running strong, but to figure out where the leak is would be a pain in the butt because the engine bay is really small.

Just wanted to see if anyone has any similar experience with air conditioning system, diy, etc. Kinda sucks that I have to drive in 95-100 degree weather. Any help would be greatly appreciated. Thanks in advance!

adding the dye is the way to test if there's a leak. if there's no leak then you have other problems. there is no diy that i know of because you need the machine to recharge the ac.

you could have a crappy thermostat....you could have a bad compressor...you could've run out of fluid n shit...also i think if the heater control circuit blows our or has a fault you can lose your AC as well.

My van actually has a leak. It's because I already brought it back to the shop twice, and the day after I bring it in, the A/C doesn't work (No cold air). So all the refrigerant and leaking somewhere. So I'm wondering what kind of dye would people use to put it in the a/c to test where the leak is? I'm asking about this because the shop I go to looks like they don't know what they're doing.

you can buy the refilling stuff at walmart and DIY.