The Ac might need service.
The compressor wont come on if the pressure drops off . The pressure is kept high by a chemical called freon. Yours is R-12 it is out of date and can be replaced with the newer version called Freeze 12. R-134 is another brand but it requires the chloro's to be removed that get left behind from the R-12. Also R-134 needs an ester based oil versus the mineral oil currently mixed in the R-12.Freeze 12 is compatible with R-12 oil. A leak can be detected with a dye and flourescent light. Another brand of freon would require all the system seals replaced, and a filter called a dryer replaced. Usually Toyota and other manufactures have dryers.
If its a small leak a new can of Freeze 12 should do the trick. Also I see Autofrost is compatible.Auto parts stores like Carquest should have it We have some here and I always see the empty boxes of the stuff sold to AC shops.of Freeze 12.
An Ac shop could do the pressure check and put some of the freon in for about $50.00 I completely replaced all my seals and old parts before I took mine to a reputable shop who charged me the for a full charge of R-134, and then $25.00 labor to put it in.
If you buy a can it might come with a hose to put it in. The low pressure side is the side to fill your AC system If you go to Walmart you ll see the different cans and some with the oil in them and some with sealers.You'll wonder why cant I use this, and people do. I never seen the brand Freeze 12.