I just bought a 2000 f250 diesel truck and am having problems with the ac. When I first turn on the ac it blows very cold and works perfectly but after about 5 or 10 minutes it will start blowing warm and slightly humid air for probably around 5 or 10 minutes and then suddenly the very cold air will come back. This cycle repeats over and over again and I'm not sure what is wrong.

 

Does the volume of the air coming out the vents change when the problem occurs and resolves?

You have a freezing/thawing problem, need to determine if it's happening internally or externally at the evaporator core./

If airflow volume remains unchanged, then it's likely due to moisture in the system.

If airflow drops dramatically, the evaporator is turning into a chunk of ice externally and is choking off airflow. Usually caused by something causing the compressor to not cycle properly (remains engaged 100%).

 

Thanks, and airflow does not change

 

A PO probably charged the system without vacuuming it first and it's moisture-saturated.

I'd open it up and inspect the orifice tube for junk first. If none is found, replace the tube and the accumulator, then properly vacuum and charge the system.

 

I haven't had a lot of time on my hands but I have done some messing around seeing when the ac does and doesn't work and just now I turned the ac on after I had not used it for the last hour of driving and noticed it was not cold. I popped the hood and went out and looked and I could see the the clutch had not engaged and the pump was not turning. I stood there for about 5 minutes and then it engaged and cold air started blowing.

 

Well, in that case, I'd check the clutch gap first. It's a common issue with older trucks and intermittent AC operation.