Sportsmanphil

My father in law asked me to fix the AC on his 98 Honda Civic.
THe problem is that late last year and again this spring, the AC would work perfect but at random would not cool. Might last 1 minute, might last 10.
I set my gauges and find the pressure a bit low. I replace the dryer and charge the freon. I found no leaks before or afterward.
2 days later he calls and said its doing it again. I pick up the car today and on the way home it cut off while driving for about 2 minutes. I cycled the AC button and it kicked back on.
I get home and put the gauges to it and find the same pressure as when I charged it 2 days ago. The car idles in my driveway for 2 hours and never failed. I idled the engine up to 2500rpm for 10+ minutes and still never failed.
It seems the problem is only while driving/under load but thats a bit difficult to test...........while driving.
I never spun wrenches for Honda and therefore am unaware of any common issues. Im hoping someone here can share some info. Ive found 4 common repairs online but some are too $$ to throw a part at it. They include ECM signal voltage, 2-way pressure switch, thermo switch and clutch clearance.
With the system working properly, I cannot test ECM signal voltage, 2-way pressure switch or the thermo switch.
Any ideas?