wierd cooling problem.. 1998 grand voyager

About two weeks ago I noticed that the a/c was blowing but had stopped cooling. I didn't immediately think much of it because I've had a/c problems in teh past, so kept on driving.
A few minutes later the high temperature warning lamp came on and I pulled over. A bit of checking things out showed me that neither of the cooling fans (main radiator/ac) was running.
After letting things cool down I drove home (just a couple of blocks) and left it overnight. The next morning I brought it to the shop (close by so it didn't get too hot) and they replaced the cooling control module.
Things were ok for a couple of days and then the a/c stopped again. This time I checked things quickly, saw the temperature gauge was climbing, etc. Let it cool off, went back to the shop, and they re-replaced the control.
Again, ok for a couple of days. Then the same thing happened.
This time they sat the car outside the shop and the fans came on... and stayed on (with occassional cycling) for the duration.
Took car home, and, eyup, you know what happened the next day.
The shop replaced the fan assembly and the controller and things were ok for, eyup, another couple of days.
Yesterday the same thing happened. I brought the car to the shop this morning and everything tested ok. They left it running for a couple of hours (oy, the gas bill...) and the fans cycled fine, the temperature stayed in the midrange, etc.
It's been working right the past few hours.
Anyone have any ideas? I've got this disturbing feeling that it's going to die out again tomorrow or Sunday...
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