The A/C in my 850 is not working properly. When I first start the car, the A/C goes on for about 5 minutes and then stops. When working the compressor clutch engages for about 10 seconds and then disengages for about 2-3 seconds. The air is cool but not cold. After about 5 minutes, the compressor clutch won't engage. I think that it may be trying to engage since there is a very slight movement of the clutch mechanism which I can initiate by discontecting the AD low pressure line switch. I orginally thought that the system was low in R134a and was going to add some. Now I'm not too sure. Any one have any ideas? P.S The A/C has really never worked properly since the evaporator was replaced 5 years ago, although then it would go for about 20 minutes before quitting.

Thanks for any help!