I have a 1998 Dodge Ram 1500 with the 5.9L. My A/c wasn't working so I bought Ac pro can an tried to charge it. I had the Ac on full blast and the compressor didn't kick on so I thought low pressure. I started to charge the system and the compressor cycled on and off every 5 seconds. Still no A/C and the low pressure gauge was in the red when I stopped charging. I have charged a few systens before but have never had any issues like this. Also when the compressor kicks on the low pressure gauge drops really low then quickly raises back to the red once the compressor is off. Also the high pressure line is covered in condensation. Any thoughts would be greatly appreciates

 

It sounds like something is plugged. It probably had a compressor explode at some point, and the system wasn't properly flushed/ replaced.
My first guess would be the orifice tube is plugged, followed closely by the condenser being plugged. On my truck (the 98 portion at least) the orifice is in the lower condenser line. I have seen some trucks with them in the line at the dryer. I'm not sure where or when they changed though.

 

How much freon is in one of those cans of ac pro? Not sure if they are for a completely empty system.

 

I'm not sure how much but I have filled 3 small systems with them

 

The big can is 20oz I think.
The system should take 32oz from evac.

 

Size of the R-134a can at most parts stores is 12 oz. Cans of R-134a come in other sizes, but this seems to be the most common that's readily available at places like Wal-Mart, etc.

 

12oz is a small can... Ive seen them in 12oz, 19oz, and 20oz... just read the bottom of the label, it should tell you.