Conversion from R22 to R407C, oil issues.

[kentbf]

We have an A/C system that is designed for R22. It has been converted to operate with R407C. Its a Carrier system with outdoor aircooled condenser and two semihermetic compressor on each condensing unit.

Out of four compressors, I now have two operating normaly. One I can see debris from the bearings in the sightglass and one is tripping on low diffpress.

So my question is, if the units came with mineral oil and the company that converted them didn't remove the mineral oil thoroughly enough. Can it lead to the breakdown of the compressor?

I have changed the oil today. filled it up with capella HFC 55. When you have opened the compressor and are vacuuming, how long do you have to keep the vacuum to be sure you have removed all moist?
I normally take it down as far as the pump goes, then fill the compressor with gas and vacuum it one more time. Is this the way to do it?

Eagerly awaiting your point of views.

Best regards
Kent.

[lana]

Hi kentbf,



So my question is, if the units came with mineral oil and the company that converted them didn't remove the mineral oil thoroughly enough. Can it lead to the breakdown of the compressor?



Yes it can. The synthetic oil is hygroscopic so care must be taken when working with it. Changing a R22 system with mineral oil to R407C with synthetic oil, has a procedure that must be fallowed otherwise the oil will be contaminated.
The simple procedure is this :

DO NOT remove R22 yet.
Drain the compressor oil as much as you can.
Fill the crankcase with synthetic oil.
Start the system and let it work for a few minutes.
Drain the oil again and fill new synthetic oil.
Repeat this until the oil contamination is less that 1%. Can be checked with oil kit.
If contamination is less than 1% now you can recover R22 and charge with R407C.About the vacuum. Pull a vacuum for 3 hours. Break the vacuum with Nitrogen and pull vacuum again for as much as you can. EN378-2000 states that the vacuum time depends on the size of the system so there is no written rule for the time. Personally I keep the system under vacuum (pump on) for 24 hours to be on the safe side. Specially for the synthetic oils.

Apart from the oil issue check the TEV, filter.

Good luck:)
Cheers

[SteveCass]

My firm has done a few gas conversions and we usually change the compressor, which helps to get most of the oil out ( part of the firm does comp. rebuilds, which helps). Then we do the system works as described above, such as a good vac / triple vac. Also bear in mind that certain valves etc may need to be changed to suit the new gas operating temps. If you still have loads of old oil in the circuit ( in evaporators etc) then you will need to change the oil in the sump several more times, then get the oil tested to check the blend of the 2 has dropped to suitable levels.

Steve