Hi all,

I've got a low temp r22 system that seems to have retained its oil in the evaporator. ( shell and tube)
i have been having superheat issues but if anything they are higher than they should be. 15 k. At the compressor.
so I'm assuming we are not getting dilution or flood back. The oil is stable in the oil sight glass, but low.We have recentley done an oil change in the compressor ( mineral oil) and I'm wondering whether the previous oil charge had an additive to assist with oil return?
Oil sep seems ok with not much oil in. The only other place the oil could be logged in is the evap, and it doesn't seem to be returning. The system has run for many years and the only thing I've done is to change the oil.
What could I add to the oil to assist in improving its viscosity at -50 c sst?

thanks.