Compressor Sluggin-Best Place For P-Trap?

[mark beiser]

I agree with a liquid line solenoid. Not pumping the unit down, just closing when the call is satisfied. Install it in the liquid line close to the evaporator. That will keep liquid from migrating on the off cycle.

I've seen them at the indoor coil and at the OD unit .... i guess it doesnt really matter

For a long line set application, with the liquid line and evaporator above the condenser, it is best to have a LL solenoid at the outdoor unit to prevent liquid draining back into the condenser and displacing the vapor in the condenser coil.
If the condenser coil and discharge line are full of liquid when the compressor starts, there will be a huge spike in the head pressure for a short time, sometimes even rather violent vibrations. I've seen trip discharge line mounted high pressure switches, and cause cracks in the discharge line due to the vibration.
Scroll compressors sound especially angry starting under those conditions.

A non bleed TXV will take care of things at the evaporator coil end of the lines.