When my wife's 84 300TD A/C is on, the cold air flows out of all the vents plus thru the vents near your feet. On my 78, this is not the case! I have no vacuum leaks and everything seems to be working fine but..... We were low on R12 so my neighbor had an extra can from his recent trip from Mexico. The stuff there is around $8.00 a can!! We put the can in and the air is now cold but... immediately the clutch started to knock!! The next morning I took it to an A/C mech. and when I tried to turn on the A/C the clutch did not go on. He got under the car and wrapped the clutch with his flashlight and it turned on. He said that the gap is wide on the clutch and it may or may not be adjustable. Since the time he hit the clutch it now works. I talked to my mech. and he said that the clutch may go out at anytime and that the compressor may freeze up taking all the belts with it! We are about to go on a 3k mile trip with four kids and the dog soooo I want the A/C to work. My mech suggests to get a new compressor and clutch ($330.) and rec/dryer and exp.val. and convert it all over to R134. I did this to my 78 300d and it works great. Sorry for the verbage and thanks for the help!!