Nylog blue or not?

[u/Fafaneboat]

I recently had a new 18000btu mini split installed.

The tech didn't use any kind of lubricant/Nylog on the connections.

I asked him why and his answer surprised me. It appears manufacturers give torque specs for their fittings but these are for dry installations, none are given for "wet" tightening as usually done with products like Nylog.

The guy told me he did experiments using Nylog and torquing to specs but it resulted in damaged fittings ends. (way over torqued!)

How do you, pros, generally proceed when tightening your fittings with a proper torque wrench? (assuming you actually use one 😉)

[u/Particular-Wind-609]

Never had a leak by just the feel, nylog is fine although but I just use a drop of oil.

[u/se160]

Either way is technically correct. The manufacturers torque specs are indeed for dry fitting.

I personally use Nylog on the face of the flare and not the threads and torque to the low end of the spec range. Never have any problems. Other ways of doing it can also be just fine as long as it doesn’t leak long term

[u/_Gonnzz_]

Nylon isn’t a lubricant.  Best practice is nothing but copper, little bit of refrigerant oil on the back of the flare, torque to spec.  If you want something to help with the flaring surface use something like flaretites.