truck change out

[simbamolly]

I'm changing a Copeland condensing unit out on a 25 year old Hackney plate truck. We will be changing from R-502 to 404a. We pulled the gas out and I blew the system out with nitrogen and I' replacing the drier and sight glass. I have read where people say to change the oil after 20-30 hours run in , but many say not to. Just wondering if anyone has been down this road and has any thoughts. Thanks

[HeyBob]

Good question, but I think you will get better answers in the Refrigeration Forum, I am moving your post there. Those guys in that forum are sharp!;)

[Carsten]

Polyolester oil is very aggresive to old dirt in the system, it will wash it from the walls of the tubes. If you have a system, what was running with black oil, with very hot temperature after the compressor, I would change the oil a second time after recommisioning.
But if you have a clean system, I think it's not important to do it. A intermixture of 3 % mineral oil shouldn't be a problem.
You will see it in the strainer of the TXV :D

[k-fridge]

I agree with above.

I will add, Be sure to remove any controls and metering devices where you can get a good blow through the system, otherwise you probably won't clear the evaporator.

If you want to be sure, get some Calgon RX-11 and flush the system with it. Done properly, that will remove most of the crud and old oil.

Best to figure on an additional drier change after the unit has run for a few days.