1998 nissan maxima not cooling

[desertac]

I have a 1998 Nissan Maxima - with insufficient cooling. I have a series of question to ask?
How can I tell if the compressor is working correctly? Yes, the clutch does engage when the climate control is "ON" not sure about the pressures.
Not sure if the system is fully charge?
I do have a FSM manual for that vehicle, but it does not say anything about the ambient button (which I do not have - even thou it does have the sensor).
The reading are as follows
Low side 25psi
High side 170-200 psi
center vent temp 92 degrees
outside temp 95 degrees
Not sure if I'm understanding what all this means, but I have add refrigerant to the system last and this year. It was cooling last year, but slowly becoming insufficient since then. The only symptom is the outlet of the THX valve is very warm to hot.
Not sure with to do or check next.
Just do not want to change parts. The problem does not appear in the range of FSM to repair. Also living out in the desert- not easy to find a good repair shop (a last resort) Would like to fix it myself. The a/c system have not been touch in over 19 years.

[Dougflas]

Sounds as if you have blend door problems. 25psi and 175 -200psi is enough to get you some cooling. If you're getting 92º from the vents, the heater is effecting your system.