How do you check the high pressure on the air conditioner for a 1997 volvo 850

Do you have ac gauges?You can only check with set of 134a gauges.Hook the red hose of the ac gauges to the large ac port on the high side ac line(it is the small ac line/hose).Do not turn the red knob on (on the ac gauges)If need to hook up low side(blue hose)to the small ac port on the low side line(it is the large ac port).If I can help,let me know.