We charged up the AC on my 85 F-250 today and not to my surprise it didn't get could. Puled vacuum for about 30 minutes and charged to the recommended amount of r-12. Problem is the compressor will run for 15 seconds and then stay off for a minute or 2 before coming back on. Any thoughts on what to look at? Blocked orfice tube, bad lower pressure switch, expansion valve??
I'm not sure if I want to spend a bunch of $$ on the AC system as this is not my everyday vehcle but it would be sweet if the air worked.

 

What's happening to the low side pressure when the compressor runs? It sounds like one of the shut-off valves is still closed.

 

The low side stays the same never realy moves? Shut off valve?????? Clue me in on this please.

 

The low side MUST be changing for the clutch to turn off. Are you sure the valve to your gauge is open? Put a voltmeter or test light across the clutch wires and see what it does when the clutch cycles.

Did someone add a high-pressure cutoff switch to the clutch circuit?

On some compressors, there are valves where the hoses connect. They have large black plastic covers screwed on to cover the square shafts. Make sure both are unscrewed all the way (but not TIGHT). Dig around the Chilton's site and you might find a diagram that shows them.