If this always worked before, something has changed.
I agree with others that the unloader is always worth checking when it comes to compressors. Another possibility is that there is a blown starting cap and the motor is starting off the running cap.
Once in a while you get shown the light
In the strangest of places if you look at it right. Robert Hunter
A friend of mine worked for a chicken processing plant and would tell horror stories about what they would find in motors.
The 95% of people that you can't trust give the other 5% a bad name.