My truck is a 1997 F150 with the 4.2 v6, auto transmission. Now to the problem my ac compressor short cycles and I have no cold air. I added a can of r 134a and it worked for about 3 days before it quit. I hooked up the guage and it shows it still full but the pressure goes up and down as the compressor kicks on and off but it is still in the filled range of the guage. The pressure cycling switch is working I guess, when I touch it I can feel it clicking on and off and the lines right behind it are very cold. I don't know where to start to look for the problem any help will be greatly appreciated as in the past this board has helped me out alot

 

The gauge only shows accurately when the compressor is RUNNING. If the pressure drops too low, the low pressure switch will turn it off, indicating low charge. But don't just keep dumping it in - get a pro to find & repair the leak. You can damage a LOT more by just refilling it.