R22 to R422d oil change

[ktm]

Just wanted to see what other peoples opinions and ideas are on the subject of oil changes when converting from r22 to r422d. We have changed a few systems over now but there is still debate in our office as what to do in relation to changing the oil. Some people are saying change 5 to 10% to a Poe and some say Change the whole lot. Obviously just leaving the mineral oil is not the way to go but is there a reason as to why only changing a percentage of the oil rather than the full amount? Interested in anyone's response .
Thanks in advance

[monkey spanners]

I'd prefer to change the lot if its practical. It would depend on the system, i think the more complex and the longer the piperun is the more important it is to have a higher POE concentration with HFC based refrigerants.

[Glenn Moore]

Hi
When R422d was first introduced it was supposed to be compatible with Mineral oil. On some systems it did work OK , on others the mineral oil failed to return to the compressor. On a site in London I helped to convert two York chillers to 422d. The first unit ran perfectly with the mineral oil in ,the second unit the oil turned grey and left the compressor never to return. At this point the system was drained and the oil totally replaced with POE . This solved the problem and to keep the units identical the other chiller was drained and filled with POE oil. All of the larger contractors as a matter of course change the oil to POE, as often oil return problems occur with pure mineral oil , this causes more work more costs etc. Also when retrofitting to 422D there can be up to 25% loss of capacity,due to the TEV not controlling the superheat and liquid injection correctly as the TEV's charge is not compatible with R422D and the TEV'S static superheat curve can cause this loss of capacity. When retrofitting these systems it is often necessary to fit electronic expansion valves that can be tuned to the new refrigerant in the system to recover some of the lost capacity,especially on water chillers, as lower suction temperatures cause chiller freeze ups and crushed tubes
But the answer is it's cheaper to replace a few % of the mineral oil with POE, than replace the whole oil charge over to the more expensive POE lubricant

[chemi-cool]

After retrofit one unit only, without changing oil, I grew a bit smarter.....
System work much better when using POE.
Oil is returning just fine.

Now I use R- 507.