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Ford Escort Air Conditioning - what's going on?

I have a 1999 Ford Escort.
4 years ago the AC stopped blowing cold. The local dealership couldn’t find a leak. They recharged the coolant. It was OK for the rest of that cooling season.
Next spring, it was again dead when I first tried to use it. Still no leak found, recharged again. This time it died 5 days later. The dealer’s next suggested step was to look for the leak in harder to reach places - hence more money. So I gave up.
This year (after 1 year with no attempt at AC). I still had the fan on one of the non-AC selections from the last time I used the heater. The temp knob was all the way down to it’s coolest setting. I noticed that it was blowing cold air. This setting normally just blows air temperature air at that setting - you need the AC or Max AC settings to get actual cool air. Turning the knob to one of those positions resulted in the cold air going away. So, the AC is mostly back, but at the wrong setting.
But it’s not quite back all the time. From time to time, it gets not quite cold while driving (still cooler than air temp, but not AC temp cold). And a few times it’s gone away completely for days at a time. And still there is no cold air from the AC settings, just from the position with the fan blowing at the feet and out the dash. One of those times it went away was started when I changed the knob position to the defog setting and moved the temp setting to a bit warmer - when the knobs were returned to their previous settings there was no cold air for about a week.
I live in Virginia so AC is important. On the other hand. This is a 13 year old car and I made it through the last 2 summers with no AC so it’s hard to justify throwing several hundred $$ at the problem. It would be nice to have a good guess at what the problem is so I can decide whether or not to make another attempt to get AC at the appropriate knob positions and without it going away for days at a time (happened 2x so far this cooling season).
Thanks.