R-422D (MO29): The Mineral-Oil Drop-In for R-22 Systems

Most R-22 replacements ask you to change the compressor oil. R-422D — sold by Honeywell as Genetron MO29 — does not. That single property is why it remains one of the most-used retrofit blends in the field.

Why mineral oil compatibility matters so much

Converting to POE oil means recovering the charge, draining the compressor, flushing lines, refilling, and often repeating the oil change to clear residual mineral oil. On a rooftop unit in August, that is most of a day and a customer without cooling.

With R-422D the job is closer to: recover the R-22, check and repair the leak, evacuate, charge as a liquid, adjust, label. The equipment goes back on the same visit.

What to expect on performance

R-422D is a compromise and it is worth being honest about that. Capacity typically runs slightly below R-22, and you may see a modest efficiency reduction — the price of not touching the oil. On an aging system that is being kept alive rather than optimised, this is nearly always the right trade.

Expect somewhat lower discharge temperatures than R-22, which is generally good for compressor longevity. As a blend it has temperature glide, so read dew point for superheat and bubble point for subcooling.

Where it fits

• Existing R-22 air conditioning that needs to stay running
• Medium and low temperature refrigeration on mineral oil
• Emergency work where downtime is the binding constraint
• Equipment with a few years of life left, where a full conversion cannot be justified

Where it does not

New equipment — R-422D is a retrofit blend, not a design refrigerant. And if you are converting a system you intend to run for another decade, the efficiency you give up will eventually outweigh the labour you saved. For those, R-407C with a proper oil change is the better long-term answer.

Practical notes

Charge as a liquid. Vapour charging shifts the blend composition.

Do not mix with R-22. Recover the old charge fully. A partial blend is neither refrigerant and behaves like neither.

Label the system. The next technician has no way to know what is in it otherwise.

Comparing options? See the full R-22 replacement guide, or browse R-438A and R-421A, the other mineral-oil-compatible routes.

Products covered in this guide

Virgin, factory-sealed cylinders. Free shipping across the US.

R422D MO29 Refrigerant 25 LB | Arctic Prince$170.00 – $3,900.00Price range: $170.00 through $3,900.00R22 30 LBS Refrigerant$199.00 – $4,733.00Price range: $199.00 through $4,733.00