Question on suction line configuration. I suggest having a trap on the suction line AT the attic evaporator (air handler). The condensing unit is outside (of course) and about 20 feet below the air handler. Seems like a good idea not having all the refrigerant oil drain back to the compressor and making for a hard start. Trapping at the evaporator should hold some oil there, right? Or not worth it at all? Residential installation, 3 ton split.
You should not trap the A/H when the condensor is lower then the A/H. You sometimes trap when the condensor is above. Lots of manufactures are not recommending traps anymore. If you have correct velocity (Line sizes) then oil return should not be a problem. My feeling along w/ many PE's is that the velocity would be good if the system was always at correct load. Low indoor, out door temps, dirty filters, loose belts etc etc, change velocity, causing lack of oil return. Some people feel that traps ( when the condensing unit is higher) cause problems such as, running the compressor low on oil because the trap is over sized, and when the trap is full and the compressor starts, it now has to swallow a throat full of oil, which can damage a compressor. Some trapping like inverted traps are needed to help in the prevention of oil migration during the off cycle. On trapping an A/H when the compressor is higher, you should use elbows and St ells to keep the trap tight and small, not the big preformed ones, and when using inverted traps, I like the preformed ones. The best thing to do is consult the manufacture for there recomendation on pipe sizing and trapping. I use a sporlan software myself for the commercial stuff, also sizes (correctly) solinoids, dryers, txv's etc. In your case though, you want the oild return to the compressor, not try and prevent oil return. Hope this helps.
Thanks a bunch Ultatec!!!
Check your install manual.
Some manufactures do recommemd a trap when the evap is higher then the condenser.
We just put a slight bow in the suction line, inverted trap.
Or if the lineset comes over top of the a/h, then you already have an inverted trap.