What's the cause of those AC pressures

2011 Ford Escape XLT 3.0. 140,000 mi.
Compressor activated on request. Constantly engaged until commanded off. Low side reads over 120 and 215 on high side. These are the readings with compressor engaged, with compressor deactivated and static. Occasionally the compressor will rumble. Any ideas why these readings are so squirrelly?