I was thinking like marc is - Low Pressure CutOff/LPCO on a CCOT system. 90 PSI isn't much for the HIGH side of an automotive A/C system. If it's R134A, the rule of thumb is 2.2 times ambient temperature. So 80*F would yield 176 PSI high side. But if LOW side (on CCOT) gets down around 20 PSI the LPCO will shut the compressor clutch OFF. In other words, if there's not enough R134A in the system to get the high side above 90, the low could well be falling below 20 and the LPCO would do its job.
OR... a bad LPCO could be cutting the system off prematurely. Some of the LPCO's I've bought did NOT come with the needed O-Ring. You can usually re-use the old one, just don't lose it, cut it, or toss it with the old LPCO. They screw down onto a Schrader Valve, so replacing one should not cause loss of refrigerant.