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Oil Compatibility Failure During R22→R407C Conversion

Likely causes

R22 mineral oil (MO) or alkylbenzene oil (AB) mixes poorly with R407C

Check: oil cannot return

What to do: Fully recover refrigerant, then drain all oil (compressor drain + pipe flushing)

Residual mineral oil remains in piping

Check: contaminated oil backflows to compressor

What to do: Charge R407C-compatible POE oil (ISO VG 68 or manufacturer spec)

R407C is compatible only with POE (polyolester) oil

Check: mineral oil causes sludge formation

What to do: Perform minimum 3 flush cycles: charge temp refrigerant → run 30 min → recover → collect oil sample → repeat

Insufficient flush cycles (minimum 3 recommended, but stopped after 1–2)

Check: Inspect with instruments or visually

What to do: Check oil contamination: TAN ≤ 0.05 mgKOH/g and moisture ≤ 100 ppm before finalizing

Flush completion judged visually instead of oil contamination measurement

Check: Inspect with instruments or visually

What to do: Install oil separator after R407C conversion (risk of residual oil from old R22 piping)

Field tip

R407C (GWP 1774) is absolutely incompatible with mineral oil. After 3 flushes, always verify with TAN and moisture readings — visual checks alone are not enough.

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