Multistack heat pump

Anyone have any problems with Multistack MS25 10/15 2HIR units? Have a problem with it cycling normally on (30 seconds in cooling, then switching into heat) then ever so often, it seems as if the reversing valve begins to modulate back into cooling, which can cause discharge to spike and trip on HPS. The relay is not chattering, no control related issue which seems to be causing this-seems to be mechanically at fault, though the valve in this unit was just replaced. Wondering if the reversing valve could be effected by a slug of oil or not-when the valve was replaced, there was a significant amount of oil in it.:rolleyes:

Could be...

Is the refrigerant charge correct? Low pressure can cause poor operation of the valve.

Brian-
You're absolutely right-a low charge can give you a high pressure fault.(how anti-everything we've learned is that?)
The charge is weighed in per Multistack. Our latest part of the puzzle is this: I have to go back out to the job and look to see how cap tubes common to the pilot activated reversing valve are tied in; if they tie from above the common line, we may be seeing an oil slug causing valve malfunction-below the line, maybe not.I'll let you know how this one turns out-
Will

I would first change solenoid coil. Or if you have this.
What was problem with old valve? Did you changed coil when you changed valve.