differant systems contain differant oils. residential a/c is the simplist and usually has only contained mineral oil in most of its applications. with advent of the reduction r-22 a blended refirgerant r-410a has been produced to take its place. r410a systems use polyoilester oil ( poe )
this oil is has been in use for years and is widely used in most screw chiller applications.
the problem with poe oil is that it absorbes moisture at an alarming rate and to further the problem will not release this moisture very easily, so if this oil is exposed to the atmosphere for any leangth of time the oil is contaminated and therefore a hazard to any system then.
for example in a residential system that developes a leak and all the refrigerant has been lost then repairing the leak as usual but now changing the drier is manditory and the compressor must be pulled and all the oil must be poured out and replaced.
now for the life of me i cannot understand why really smart engineers are so stupid. i guess most buy theres any way.
why is there not a drain plug to remove the oil because now the manufactiure will have to replace more compressors and more condensers are going to be changed sooner because this is residential where most techs are schooled for quickness and most are not going to pull a compressor and do this. This is my opinion but if a residential tech cant figure out an airflow problem and corrects it with dumping excess amount of freon in a system to overcome it then where are we are with poe oil. !!!
Oil drain plugs could cure a lot of issues, but unfortunately could also cause a lot of issues because most residential techs have no clue as to how to proper put oil into a system. This would require a whole new training process.
Incidentally, the reason for using the POE oils is that mineral oils are not picked up and carried through the system with certain blended refrigerants.
ok ok so I guess I will fess up and say Im one of those residental techs that would have to be trained the right way to replace the oil in the compressor. I know I have added oil on some r22 systems that you were running longer linsets that the manufacture required adding so much oil per foot over a certain amount.
geez, and I was thinking Norm would be going.....ALL RIGHTY, ANOTHER CLASS I CAN TEACH. Probably not all that much that anyone that has a pretty good idea what they are doing would need a whole class pertaining to just replacing or adding oil. Would think that could be added into another class tho. I can see Norm drooling at the thought of a new class.
When the federal government set dates for the phase out of CFC's and HCFC's the industry reacted with a new family of refrigerants called HFC's. These refrigerents are not mincible with mineral oir or AB oil so POE was developed as a lubricant for them. Those of us in commercial refrigeration have already enjoyed (insert sarcasm emoticon) a few years experiance with R-134, R-404, R507, and now air conditioning gets to join the fun (repeat sarcasm emoticon) with the transition from R-22 to R-410 which is also an HFC refrigerant. Frankly, POE has it's problems and we refrigeration guys have been begging for an alternative, but as of now this is about all we have to work with HFC's in HVAC/R application.
Extra care must be taken when working with HFC/POE systems. They are incompatable with other types of oils, as a rule of thumb any existing piping must be cleaned of old oils to where the system will not have more than a 95/5% mixture of POE/other oils. Also, POE is a strong solvent so it will clean up any crap in an old system and likely deposit it in the drier or metering device. These are more good reasons to replace the entire system when going to R-410 equipment.
One of the biggest challenges with POE is that it's extremely hygroscopic. That means it absorbs moisture very rapidly. I emphasize rapidly, it sucks up moisture like the government sucks up taxes! (OK, that's pretty doggone fast). Care must be taken to not have the system open any longer than neccesary, good vacuuming procedures are a must, and new driers are crucial. Basicly just good refrigeration practice but 10x more critical then it used to be. If the oil gets moisture contaminated you won't remove it by pulling a vacuum, you gotta change the oil.
One thing we have seen on the refer side with POE, when a unit has been running high discharge temps due to a dirty coil or low charge situation, the oil tends to coke (turn to something resembling charcoal) and plug screens, metering devices, etc. Also hot gas valves and reversing valves have been more troublesome with R-404 and POE. This is something to watch for on the A/C side as well. Preventative maintenance is even more important than it used to be.