what is the reason for increasing the size of the suction line on a scroll type compressor when the run is over 15'? Frigidaire says to up a 3 1/2 ton suction line from 3/4 to 7/8 if the pipe run is over 15'? the only reason that makes sense is oil return, because of the different design?
i have to replace a 3 1/2 ton carrier condenser that a "large ny area contractor, that also sells a lot of alarm sytems" cut the lines with a hacksaw - wires and all and then proceeded to destroy the suction line quick - connect threads with a channellock to ensure replacement.
The owners are good friends that happen to be building an extension and the lines were in the way of the roofer, so rather than "bother" me they called this hack. after he shot them a zip code price to replace the unit they then decided to "bother" me.
my quandry is this... the run is about 25' and am considering replacing it with this frigidaire scroll but am concerned about the line question. the existing line set is 3/8 - 3/4. and would rather just splice the 10' that they cut off and run the 3/4 but ultimately want to do it correctly. any help?
additionally can anyone direct me to a source of on line manuals for hvac equipment?have searched hi and lo but ng so far thanks all

[Edited by madmark on 07-19-2005 at 04:58 PM]