Unless you have a very late model '93 you have R12 in the car. I have an early '93 and it's R12. (R12 = expensive)
You obviously have a leak and since you aren't saying anything about mechanical or electrical problems I'll go on that assumption.
1st. Call Toyota dealer. Give them your vin number and see if your car qualifies and has not had the EXPANSION VALVE recall from the early '90's performed. If it hasn't had the recall you may be in luck. They will replace the valve & fill the freon for free. This is over $500 at the dealer.
2. If your car doesn't qualify find a friendly mechanic. Toyota Dealer cost of valve is around $175. R12 is AROUND $60 a pound and you will need 2 of them. It's around 3 hours to fix. Valve is behind the glove box, burried.
If you do need R12 check locally for a substitue called FREEZE12. This is a direct replacement for R12, unlike R134. I am running it. It works fine. Do a web search for
www.freeze12.com
If you do put in FREEZE12, put in 2 pounds with LEAK detector and run it for a while. Find out where the leak is. Max, $40 to put in 2 can.
3rd. You can not do it yourself / change freon. R12 requires a license to buy and a machine to install. Too much is as bad as 2 little.
Sorry for the grimm info. Hope the Toyota recall works for you. If not RUUUUNNNNNNNNNNNN away from the Dealer. U will be finacially taken out-back and whipped by them.
Good Luck