Need advice on dealing with A/C in old car

I have a 1990 Plymouth Sundance. Odometer says 125k but it broke several years ago. So heaven only knows how many miles are actually on the car. I
bought it as a program car with 5K miles on it, all the other mileage is mine. It's been a great car and I've kept it maintained and it's in decent mechanical shape for a car its age, albeit the body and interior are getting a bit ragged.
The air conditioner worked fine during most of the life of the car, I think in 14 years I only had to have Freon added a handful of times, which surprised me. Anyway, in 2004 the A/C quit working. I took it to an A/C shop and they gave me a six-foot-long list of what was the matter with it and basically told me it would cost more than the car was worth to fix it and that I ought to let them recharge it and try to sell it quickly as-is before the air quit again. I left that place and never have and never will be back, basically because of that last bit (as well as the fact that they ripped my father-in-law off). I have this funny habit of wanting to be on the up-and-up with people.
I then took it to my main mechanic, the guy who does all but the heaviest work on my cars, and he said, "Shoot, let me have a shot at it," and he changed the thing to R-134, filled the system and the thing worked absolutely fine for two entire years.
In spring 2006, I noticed that the A/C had quit working again, took it to my mechanic and he filled the system and it worked fine throughout most of the summer. Then in August ... really good time to have A/C problems in the Deep South, LOL! ... the clutch broke off the compressor as I was driving down the road with the A/C working fine. After I finally tracked down a clutch (more on that later), my mechanic made the repairs and filled the system again and everything was fine, but I noticed in late September, as it was still a bit warm and I was running the A/C, that it had quit again. In hindsight, and this is strictly anecdotal and off the top of my head, but I wonder if the clutch breaking off ... and it sounded like the freaking engine had disintegrated when it happened ... really damaged something even more in the A/C.
My mechanic recharged the system again on April 2, this time using some refrigerant that contained a stop/leak formula. The A/C worked fine until yesterday, when it quit again.
I know the first thing everybody is going to say is, "Get another car." That isn't an option. This is one of the sacrifices we are making to send two kids to private school. Basically, we're going to run this one until it quits before crossing the bridge of replacing it.
I have, in my storage shed, a recycled A/C compressor that will fit the car. I bought it last year when I was looking for a replacement clutch, because a replacement clutch was like twice as expensive as the whole compressor. I figured I'd take the clutch off the compressor and use it and save some money. Until I found out that it wasn't the EXACT compressor and clutch, just one that would interchange with the Sundance if you replaced the whole thing, so I ended up having to buy the clutch anyway. But this one is sitting there ready to be installed, all I'd be looking at is probably the cost of a new hose assembly and labor.
The thing is ... and I've discussed this with my mechanic, and I'm about to go see him when I get up from the computer, I just was looking for some other input as well ... I'm afraid that if I have the compressor and maybe a new hose assembly installed, it might wind up that the condenser or the evaporator is actually what's leaking.
Given what I've said here ... and I've made this lengthy to be as detailed as possible ... how would some of you A/C folks recommend that I proceed here? I know there is some leak detector with dye in it that will show where leaks are, should I get my mechanic to do that?
Or should I just quit trying to put bandaids on this ancient car and roll the windows down ... the only problem there is that the Sundance is so aerodynamic that I can roll the windows down and drive 70 mph on the interstate and not enough air to muss my hair will get into the car.
Thanks in advance for any help. :)
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Followup, hopefully shorter ... the Freon hasn't leaked out, the same thing that happened last summer, the clutch plate flying off, was about to happen again, the thing was barely hanging on. And that part of the compressor seems to be pretty much trashed, my mechanic was unable to retighten the nut that holds the plate to the shaft, he checked with a flashlight and dental mirror and the shaft area itself is damaged, plus the key-pin that sort of helps hold the plate on the shaft was shredded. That same thing happened last time and I absolutely could not find a pin to match it and my mechanic engineered one and isn't sure he can do it again. Basically, because of the damage and to keep from having to re-engineer the key-pin every few months because it's apparent this is liable to happen again, we're going to go ahead and install the other compressor and keep our fingers crossed that nothing else is the matter.

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On Mon, 21 May 2007 13:37:08 -0500, "Greg Bailey"

The compressor is locking up internally and this is why the clutch keeps getting twisted off. You will need to replace the compressor, flush the system and replace the dryer and metering device.
I would not use an unknown used compressor unless you just can't possibly afford a rebuilt. acsource.net has great products at fair prices and stands behind them (no, I don't work for them but have bought a LOT of stuff from them). I say this because if the old compressor is bad then you have to pay for all the labor, dryer, flush and metering device all over again which is usually the biggest part of the cost.
There is no reason that the a/c system can't be kept operational and reliable on this car. I have fixed a number of systems up to 30 years older than your car and they are reliable (although a bit leakier than yours should be when it is fixed).
Steve B.
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Price is a concern, I've already bought this compressor ... and it came with a year's warranty, which is about half gone, but it still shows that the recycler (FYI, got it online from a place in Massachusetts) was confident enough to stand behind his merchandise ... so we're going to give it a shot, if I need to do something else we'll cross that bridge when we get there.
wrote:

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