Trapped refrigerant lines?

With cooling only air conditioners, with condenser/compressor on the roof and evaporator inside either on ground floor or first floor (below condenser) would a trap need to be installed in the suction or liquid lines? Should horizontal runs be sloped?

Mainly concerned with 1.5-5 ton R22 systems here.

Thanks.

source https://hvac-talk.com/vbb/showthread.php?2225710-Trapped-refrigerant-lines&goto=newpost