AC pressure at idle vs higher RPMS

I feel stupid asking this question...

At idle with my AC running i am sitting around 35 PSI.

When i rev the car (or, i assume, when i am driving), the pressure goes to around 15 PSI.

Assuming this is not normal, do you think my expansion valve is not functioning correctly or is the pressure supposed to change with engine speed?

How are you checking the pressures, gauge valve closed or open (Should be in closed postion).

Sounds like you have a low pressure issue. At 35 psi clutch cycles but pressure drops 15 psi disengaging clutch.