Since there are multiple paths the nitrogen you blow in the coil to push the flush out, nothing says it will all come out. Odds are a lot will sit in the bottom of the coil and your nitro will go through the higher passes. Your long vac was likely trying to boil out remaining flush. With dry units everywhere and cheap, I'd go that route personally.
And the flush will dissolve in vacuum oil just like refrigerant dissolves in compressor oil being oil soluble chemical. Since boiling point of flush is much higher than refrigerant it will build up in vacuum oil. As it does so the vapor pressure of vacuum pump oil rises and the performance and efficiency drops dramatically. You can actually smell the flush chemical in oil used to pull vacuum after a flush. Depending on how much flush you have to get out by evaporating with vacuum, you might have to change the oil more than once. You could use used vacuum oil(but not used with flush) to get the bulk of flush vaporized. Used oil is inadequate for final vacuum, but more than good enough for flashing off liquid flush chemical which doesn't require much below 15,000 microns.
You could get by with used-once oil to get the bulk of the flush vaporized and do a final deep vacuum with new oil.
I think the coil should be replaced,although if i did not replace it i would blow it out with nitro and use it would not flush it if it is a piston coil iwould remove the piston before blowing it out . I am leaning more to a small amount of oil mixing is not a problem
If the coils rated for 410A and you install a txv, dont worry about the oil, unless its contaminated. It has nothing to do with being a Pro. If the customer has the money, you could do the airhandler and the condensing unit. Its really a money issue which way you go. The coil has a sticker on it telling you what its rated for.
the hole oil thing is a bunch of hooeeey..... get out what you can and move on..... we are being lied to ....
I don't know if its a bunch of hooeeey but I do think it's over exaggerated. I've only done one system where I left the coil in & changed the outside unit to 410A & its been two summers so far without a problem. No flush at all & just blew it out with nitro. It was a heat pump too. I guess only time will tell.
An engineer designs what he would never work on.
A technician works on what he would never design.
There are many anecdotes but no scientific study where residual oil was the sole cause.
It's certainly possible that residual makes it more susceptible to technician short cuts/incompetency but no demonstrated proof that residual oil adversely affects HFC conversion.
Supermarkets are in real trouble moving to HFC-404A from CFC-502 and HCFC-22 if that were the case. You would have to dye the existing oil pink or red, then repeat the oil change and flush with POE until you can no longer see pink in drained oil and flush solvent.
Listen to baldloonie, he is telling you right, you will never flush a coil succesfully. I would be willing to say that if you try to flush the coil and change the txv, the compressor on that 410 unit will be dead within 5 years!!