i recently had 3 split units hooked up on a 16 foot rise,2 of those a/c were hooked up by one fella and when the other guy came to hook up the last he said that there must be a trap put on one of the lines so oil can get back to the compresser.the first guy had not done so,he was concerned that the compressors on those 2 that the other fella hooked up may blow.i asked the installer #1 about this and he said he didnt know that and he was going to get back to me and when he did he said that this was not applicale to that.who should i believe installer 1 or 2.all unit are 5 ton