This system is NOT supposed to be using the low pressure switch to cycle the clutch.
Thats why there are discharge temp sensors and a sensor in the evaporator. The control head is in full control on this one.
So... if you're getting a low pressure trip code then that means at some point during your drive, the suction pressure is getting too low. Was the system thoroughly evacuated with a new drier installed? You probably have moisture thats freezing inside the system or a partially plugged metering device. You said it happens at 65mph aka highway speeds yes?
I say evacuate because some dudes think putting a vacuum on an AC system for 5 mins is good enough when that is very much not the case
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