I am having problems with no water pressure or very low.
if you're getting "some", then your pump clutch must be engaging.
could be lots of things causing it.
Have you tried turning the 3-way valve to hi-med-low position to see if it makes any difference?
If that does it, one of your unloader valves has failed and/or the pressure adjustment nut has loosened
Could be sucking air causing lack of pressure
Easiest way to check that is plug your fresh water garden hose directly into the plenum (the brass bar near the rear left side of unit with several hoses plugged into it)
Follow the hose from the water box to the plenum, Unplug it and direct connect your fresh water hose there.
Turn on the water and look for drips.
If none, you'll know no air leaks from that side of plenum to pump.
With hose still connected and water on, now fire up the unit and turn on the pump.
If pump pressurizes, you have an air leak upstream of plenum
those are a couple simple things to check first.
..L.T.A.