R-12 covert to M079 ?? walk in freezer

[kurt s]

Ran into a walk in freezer that was originally R12.. It had a note about being converted to R-502. Than a more recent note saying its been converted to M079... the suction pressure is around 25psi and the freezer is holding around 18 - 20 degrees. I thought M079 was a replacement for R22 ??? should i try topping it off with M079? has anyone seen this before? Not sure what to do. They have been complaining it stops running and gets to warm sometimes but i think its just the setting on defrost timer. seems that refrigerant is low also... ???? any thoughts?

[chemi-cool]

I have converted a cold room from 502 to 422A [mo79] about a year ago, no problems and runs fine

[doctor freon]

MO79 (R422A) is a good replacement for R-502 etc. MO99 (R438A) is a better match for R-22.