96 Dakota A/C Problems

I have a 1996 V6 2wd dodge dakota. When I turn my a/c on, I only get warm air coming from the vents. My compresser turns on for 2 seconds then turns off. It will continue to turn on and off every 5 seconds. I've checked my a/c lines and they are full, so it isn't a leak. Anyone have any idea how to fix this problem. Thanks

How did you check the A/C lines to determine is they were full?

Two ways. One way was, I purchased a recharge kit. A tool came with it that you put on a capped nipple on the line, turn the air conditioning on, and wait to see if the pressure reaches a certain mark on the guage. If it reached the mark the lines are full.
The second way was ensuring that the lines going to the condenser and the expansion valve were approximately the same temperature when the a/c was running.

I assume you took the pressure readings when the A/C compressor was actually running? If the compressor is only running 2-5 seconds that could be difficult. If it is full, it could be the a pressure sensor is not working correctly affecting the compressor cycle, also there is a dryer that can become ineffective and cause problems. I'm not an A/C mechanic so I can't offer a definate solution, I have fixed the A/C in my '00 GC before though. It had the opposite problem, the Compressor ran all the time B/C the refrigerant was low.