ok, if the r134a level is good, then next cause of this symptom is exapanison valve freezeup. happens when there is excess moisture in the refrigerant and it causes the water to freeze up where the liquid freon goes through a tiny orifice and expands to a gas in your evaporator (and gives frosty cool air)
you can't fix this yourself....here's why:
search for a coupon, then go to pep boys, goodyear, or whoever, and have them suck all the refrigerant out, change out the dessicant/dryer assembly, then recharge it with 134a and the right oil. that will fix your problem...but you have to get out all the moisture with a vaccum pump for quite some time.
for around $100, you should have working a/c again.
OR: go to pep boys, napa, kragen, look for the little a/c bottles that can fix these little problems...you need the can that will claim to get rid of excess moisture in the system. they sell them for around $10 and might be worth a try first. the stop leak has worked well for me.
let us know what you decide.
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