I need air!..please help

[csona]

I have recently purchased a 98 dodge caravan. We were aware that we would have to do something to the air conditioning system and that there was an oil leak.
First we brought the van to a shop and they said the compressor was bad, they replaced the compressor, the belt, the dryer and flushed the system (before we picked it up, the clutch on the remanufactured compressor locked up and they replaced it under warranty).
We brought it home and began to hear some infrequent screeching from what seemed like the compressor. In the mean time, after some trial and error, we feel we fixed the oil leak, which was the o'ring under the distributor.
Then the compressor quit kicking in. They replaced it one more time, the only thing that the didn't replace was the H valve (expansion valve)but we feel that something is making the thing break and we really have no idea!! One more thing that is happening since we bought the van it that the lights on the ac/heater panel are flashing.
Please , please help.
Thank you so much!!!!!!