Replacing an Old R22 or R410A Wall Mount Air Conditioner: What to Check

October 9, 2026

Wall mounted air conditioner on the side of a building

A lot of the wall mount units on shelters and modular buildings today went in 15 to 20 years ago. Many run on R22, which is no longer produced, or on R410A, which is being phased out of new equipment. When one of them fails, the replacement is a new R454B unit. Here's what to check so it goes in smoothly.

1. Capacity

Don't assume the old tonnage was right. Equipment loads in shelters grow over the years, and classrooms get more computers and people. If the old unit ran nonstop or couldn't keep up, the load may have outgrown it. If it short-cycled, it may have been oversized. Our sizing guide walks through the load calculation.

2. Wall openings and mounting

Measure the existing supply and return openings and the mounting footprint, then compare them to the new unit's spec sheet. Differences can often be handled with transition pieces or by adjusting the openings, but it's better to know before install day.

3. Electrical

Match voltage and phase.
Check the new unit's minimum circuit ampacity and maximum overcurrent protection against the existing breaker and wire size.
Check the electric heat size. More heat means more amps.

4. Controls

Older shelters may have a lead/lag controller or alarm panel wired to the old units. Confirm the new units are compatible or plan to update the controller at the same time.

5. Refrigerant

This is the easy part. Wall mount units are factory-charged, self-contained systems, so there's no field refrigerant piping to match. You're replacing the whole unit, and the new one simply uses R454B. More on that in our R454B guide.