A/C blows hot on 1999 Chevy Cavalier

You just need a recharge.Go to an auto parts store and get a single can of R12 and the recharge line.Find the fitting on the AC line that the recharge line fits on(there's 2 but only fits 1)and hook the end on the can then on the fitting.THEN screw the puncture screw into the can lid to puncture the top of can,then turn that screw back out to release the Freon into the line and into system.To be sure you get all the Freon out of the can,stick the can in a small bucket of hot water while it's recharging your system.That's an old timers trick I use and it works.Once empty,remove the line from the fitting on the system first,remove the can from the line and save the recharge line.Ya may need it again one day.Engine must be running with AC on full when recharging the system.Stay Cool dude.

sure can, best bet too

If this was happening to me.... I'd goto an airconditioning re-gas centre and get them to check for gas leaks. In my old commodore the Evaporator Core was leaking and causing some of the issues you have mentioned.

you have moisture in the system this causes your expancion valve to freeze up an stop working, thats why it works for sort time and when it de-freezes stars working again. you need to do a EVAC & RECHARGE with a good AC service equipment, specially attention to pull vacumm por at least 20minutes so you get all moisture out of the system.
Good luck

I have a feeling that no one is checking the blend door in the plenum.

might just be a bad engine coolant temp sensor , it tells car computer engine temperature and computer controls fans , as for recharging a/c , did you pull system under vacuum ? to check for leaks ? vacuum also helps remove air to get a better charge because air expands

Its a leak ...probably concealed like in an evap housing or rear air unit and lines (if it has that). Prob at this juncture I would remove all the freon and bring system into a vaccuum with a pump and see if it will hold vaccum for an extended period of time. A bad leak will not hold srong vacuum very long and much cheaper than wasting expensive and enviromental un0friendly refrigerants.

More likely the recharge blew a o-ring and you have a leak. When your Cavalier was blowing hot air and a recharge fixed it that means it was low on freon which lets o-rings dry out, go back to the shop and have them leak test it. They use a pressurized dye to find the problem. If it's blowing it's not the cooling fan relay, they may have meant compressor relay but I'd have a leak test done first it's not expensive and easier that chasing unknown possibilities.

they prob blew the charge on the a/c it will have to be recharged

sounds like the system is either low or out of refrigerant. There is a low pressure switch in the system to shut it down in the event of freon loss. First , verify , then test for a freon leak. Once repaired, and recharged, will blow cold air again.