98 grand Cherokee a/c hot air??
 

98 Jeep Grand Cherokee a/c hot air when on worked last year.
With a/c on and fan on high. The a/c pressure goes up to 50 psi then when a/c compressor clutch kicks in it goes down to 15psi then when clutch disengages it goes to 50psi


Any ideas what it could be? Dirty evaporator?

Your system is low.

Pressures really depend on the ambient temperature and humidity. BUT low side pressure should be 30-35 psi and high side pressure 150-200 psi. Numbers are really just an estimate, but should be in that ball park.

As long as there is still refrigerant in the system, you are ok to add. I would get cans of refrigerant that have dye and oil in them. That way you can find the leak. Legally your not supposed to charge a system that has a leak. And if it's low, there is a leak.

Start by adding a can and see where your pressures are. If you can get it into the 30-35 range. Call it good enough.

Low side port is the smaller diameter port. And the High side port is the larger diameter.

What JVMopar said.