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Question DetailsAsked on 10/29/2016

Can you change just the cond unit on a r22unit and still use 407a

R22units company tells me to just change cond unit only then put 407a in it.

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2 Answers


When you say cond unit I presume you mean the evaporator, not the condensor - though that might have to be changed too, depending on unit ratings.

Some R-22 (Freon) based units, especially ones made close to the changeover date to R-410a, can handle R-410a. Most require a different evaporator and adjustment of the variable TXV valve to run at the increased pressures (or TXV valve replacement if yours is ont adjustable). The evaporator unit has to be rated to work with that unit with R-410a, however - will be a larger cooling area unit because R-410a is not as efficient a refrigerant.

Some units can also change over to 407c (you said 407a, but that is a 404a replacement - I think they meant 407c, not a - I find nothing about 407a being an acceptable replacement for R-22).

With older units, finding a compatible evap unit to use with R-410a can be a problem, because the units were not designed to run R-410a so no rating tests or certifications were done for evaporators with that refrigerant. R-407c is more likely to work, though compatibility still needs to be checked, becdause the operating conditions are not identical.

You also have to check the lineset tubing and the TXV valve and compressor and such to make sure they are rated for the higher pressure that R-410a runs at. This usually kills older units because they were made to run at the R-22 specs. many older unit compressors can't even get up to and hold the pressure needed with R-410a, and many of the older linesets are thinner tubing that is not rated forthe R-410a pressure. R-407 runs best at a different pressure too, but not as high as R-410a, so your equipment may or may not be able to produce the pressures (high and low side) that is needs to work efficiently.

If it sounds like this sort of conversion is an iffy thing - right you are. Not only in terms of finding parts that are compatible with R-410a/R-407c use, but also because the original unit was designed and rated for R-22, so even if you get it working the amount of heat it can remove from your HVAC system is commonly going to be about 10-20% less than before - meaning it will either work harder and longer per cycle to cool your home, any possibly it will be undersized in the hottest days and not be able to get the temperature down to your desired level at all, so it will long-run (run almost continuously or sometimes actually continuously for hours on end, or until the overtemp protection breaker kicks it off.)

Also - even if all the components can be found to do the conversion, essentially all R-410a uses one of several different lubricants - usually POE (polyester synthetic oil equivalent) so not only may what you put in the system not be compatible with your compressor, but you also have to flush the entire system of the old lubricating oil before recharging, because the various oil types are almost always not compatible and can result in gumming up of the system or "slugging" of the oil mixture in the compressor, which can cause comporessor failure. Also, because the 407 series runs with POE or similar synthetic, usually all seals have to be changed out because the old mineral-oil retaining seals commonly disintegrate in POE.

Personally, I would not recommend such a changeover just because by the time you get it done you have sunk 1/2-3/4 as much as a totally new system in most cases - with little or no warranty (as opposed to the typical 1 year mechanical and 5 to 10 year coil warranty on a new unit), so normally rebuilding an older unit to the newer gas just does not make sense.

Before going ahead with this I would talk to another well-rated Heating and A/C contractor about his recommendations and thoughts on such a conversion for your make/model/age of unit.

Here also is a link to a similar related question with answer which might help too -

Answered 3 years ago by LCD



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