98 Savana with 120,000 miles 5.7 with front and rear heating cooling. Replaced the A/C compressor probably at 50K (just a guess) so it is not the factory compressor. Use the van mostly for vacation and high way travel.

Since the 2nd compressor was installed I could hear it turn on and off going down the interstate or at idle as I don't recalling being able to hear the same on the original or on my Sierra (sounded like a little diesel engine). Anyway it seem to work fine for the 50K it has been in place. Just returned from a 3600 mile trip and the last 400 miles it seem to stop working.

Symptoms are: Can't hear the compressor turn on and off. Vent temp will be cold then not. When the system seems to work it only last about 3 - 10 minutes, although it did seem to run for about 30 minutes near the end. Humid inside the van. Sitting idle compressor doesn't turn on when you turn the system from vent to A/C. No condensate dripping from the rear or the front underneath the van.

Unsure of voltages or pressure because I don't have the ability to do either one.

Any suggestions?

could be low on freon. a lot of those wont run when low on freon. driving around maybe makes the freon move enough for it to come on for a bit ours did the same thing. just bought an after market freon kit and refilled it myself. you may want to see if you can see a leek anywhere.

agreed, the pcm controls the compressor and it wont turn on if you are below the minimum pressure in the system