Air Conditioner what is the low side pressure range? and what is the high side

What is your question?

I Assume the low side is 45 and the high side is 250 but neede to verify I have a ac Gauge Air conditioner blows out hot air added freon but at 42 psi the ac pump kicks on and psi drops to 12psi then up to 42 down to 12 at 40 psi the motor does not kick in