Low side with high pressure and High side with 150psi

[Notnilc20]

Car is a 2009 volvo s40 rurbo. ac compressor cycles on and off. Stays on for about 5 seconds and shuts off for about 15 seconds and repeats. When I hook the manifold gauges up while car is off, the low side was over 300psi and the high side was around 150psi. Then I start the car and turn the ac on. The low side drops to about 100psi and the high side shoots up to over 400psi. then the safety switch kicks on and shuts the compressor off. then this basically jist repeats. What could it be? Thank. Car is an 2009 volvo s40 turbo. thank you.

[Diametric]

That vehicle uses R134a refrigerant.
Pressures when the vehicle is not running should be very close to the Ambient temperature in F at your location.

300psi with the vehicle not running might might indicate an overcharge condition.
Low side at 100psi when running sounds too high to me.
But the cycling sounds ok. Is there cold air coming from the vents when the AC is on?

There could be other issues but I would recover (please don't vent to atmosphere) some R134a to bring those readings down. It could also be your gauges are not reading correctly or you have the knobs partially open.

Tim and JohnHere are professionals in this field and I would go by their advice. I do a lot of AC stuff on my own vehicles but have had no formal training although I am EPA certified for commercial refrigerant purchase and recovery and study AC refrigeration on my own.

[JohnHere]

The problem might be elsewhere, but right off the bat, it sounds like a gross overcharge to me.

Has this system ever been serviced?