Hard and soft steering

Hi,

Get extremely hard steering, then soft, then somewhat hard, then really hard, then soft for a split second, then back to hard, etc. Etc. On my car.
Fluid is fine, no warning lights on dash, air suspension is intact and works perfectly. Steering linkage is fine and is not subject to the Ford recall. No leaks of power steering fluid. But must turn wheel with two hands when steering gets hard. Only when it is rainy/damp out does the problem go away completely.
Thank you