Not sure if I have a problem or not. I have a 2005 Silverado 2500 HD Ext cab. My AC unit seems to constantly cycle on and off. You can feel the compressor clutch kick in for about 3-4 seconds and then dissengage. So I get a burst of cold air and then semi-cold air over and over. Is this normal operation? I also get much colder air when going below 50 mph. For example on the drive to work today, temp was 100. Cooling was ok driving at 60-70 mph. Slowed to pull into parking lot and temp from AC must have dropped by about 10-15 degrees. Air was extremely cold. Could this be due to fan clutch on the engine disengaging at higher speeds? Is this all proper operation?

 

Sounds like it is low on freon, cutting out on low pressure as soon as compressor engages.
Have it checked for leaks and refilled.

 

Took it in for service and truck is like a refrigerator now, Was low on freon.