The air conditioning in my 2002 Subaru Impreza has sort of worked the last couple years. This year it got bad enough that I began trying to fix it, but even though it's totally useless on a 30 minute drive on an 80-degree day, it still puts out 40-degree air for almost a minute at the beginning of the trip (so the compressor runs, obviously).
So I decided to try to recharge it. I did this, and the pressure both before and after the recharge was basically 0. It was an 18 oz can. I did this with the car running, and after I was done the air that was blowing was hot, so I figured it didn't work.
Then, on my first drive, I got cold air for probably 3 minutes - longer than normal. It kind of came and went though - unsure if it was tied to throttle/speed. Anyway at the end of the three minutes it didn't just blow hot air, the car started "coughing" every 4 seconds. Like it was trying to start the compressor (guessing) and some safety mechanism was saying "uh, nope, abort that" and there was a noticeable hiccup in my engine/speed. I turned the air off and this went away immediately.
1) I have some problem other than low refrigerant and now that I've charged it I have an overcharged system that still has the original unknown problem.
2) I need even more refrigerant, because it's working better now and air conditioners with low refrigerant tend to freeze up during use and maybe that's what's causing the hiccuping. It's anyone's guess if I have a super-slow leak that took 12 years to get to where it is or if I have a really fast one that makes recharging a waste of money.
I guess the immediately question is whether I should try more refrigerant or if I should go immediately to the catch-all answer of "take it to a mechanic to test for leaks and other problems and between 100 and 900 dollars later come home with working AC." Or, is there any other troubleshooting I can do at home?