PSA: Got schooled by a retired guy about compressor oil the other day

I was swapping out a compressor on a walk-in cooler last Wednesday and this old timer who was watching me work asked what oil I was using. I told him standard POE and he just shook his head. Turns out the new R290 systems need a completely different oil viscosity and I had been using the wrong stuff for like 6 months on these smaller units. He pulled a bottle of some Mobil alkylbenzene oil out of his truck and showed me the spec sheet. I never even thought to check because the system looked the same as the old R134a ones. Now I feel like an idiot for not reading the manual closer. Anyone else had a little detail like that totally change how you approach a common repair?

3 comments

3 Comments

jade_johnson14d ago

Hold on a second, your story is good but your chemistry is a little off. POE oil is actually still fine for R290 in most residential setups, the real issue is the moisture and acid handling because R290 is way more sensitive to contamination than R134a was. The alkylbenzene oil that guy had is more of an old school choice for R12 and some R22 replacements, not a standard thing for R290. You probably just need a specific POE viscosity like 32 or 46, not a whole different oil type. Not trying to sound like a know it all, just don't want you to go chasing the wrong fix.

umar5912d ago

Wait, is that really where the confusion usually sits though? Because @cameronn62 I think you hit on something bigger than just viscosity numbers. What a lot of folks overlook is that R290's lower critical temperature means the oil return characteristics change too, not just the contamination side. So even with the right POE 32, if your system isn't designed to keep the oil moving at those lower discharge temps, you're still gonna have issues. That's why some of the old R12 guys get tripped up, they try to use the same compressor specs and end up with oil pooling in the evaporator. The moisture handling is definitely the main thing, but I'd argue the oil return path and line sizing matter just as much for a long term install.

cameronn6213d ago

Yo, that bit about R290 being way more sensitive to contamination than R134a really clicked for me. I used to think POE was basically the same across the board, but you're right, the moisture and acid handling is where it gets tricky with R290. I honestly thought you'd need some special oil for that, but now I'm seeing it's more about picking the right viscosity like 32 or 46. Your point about alkylbenzene being old school for R12 makes total sense too, I was probably mixing that up in my head. Definitely gonna stick with POE from now on and just watch the moisture levels closer.