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Question DetailsAsked on 6/8/2017

Is it possible to have both an indoor A/C unit running on 410 coolant and an outdoor unit running on R-22 coolant?

When I purchased my home, the indoor unit had been replaced as of Dec 2014 along with a 410 sticker on it stating that it would take 410 coolant instead of R-22. My outdoor unit is a bit older (2004) but takes R-22. I had a technician out this morning who told me that there is no way this is possible. He stated my indoor unit MUST take R-22 because it runs off of the outdoor unit which is R-22. I'm receiving conflicting information and I only want to be sure as it could eventually cost me a lot of money if the wrong coolant is put into my units.

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If you have two totally separate systems (say for a large or very strung-out house), or one with central A/C plus a secondary through-wall or mini-split unit added later to provide added cooling capacity, certainly. Ditto if you have (though extraordinarily rare in a residence) a refrigerant-to-refrigerant heat enchanger unit system - with A/C outside passing its refrigeration gas into a heat exchanger inside which then uses a different gas (presumably due to newer system) which then passes through evaporator coil(s) in the house. Sometimes used in large commercial units, especially ones running flammable gases or ammonia as the refrigerant, keeping that outside (like in a roof unit) and using a safer gas to run to the interior central air or split unit evaporator coils. But I have only seen that sort of system in about 500 ton capacity and larger units, and normally only in ones in the thousands of tons capacity range.

But if you have just one outside compressor unit and one (the normal case) indoor central heating/air evaporator coil or maybe an independent indoor A/C air handler with evaporator coil, the tech is right - the regrigerant that runs through the outdoor compressor/condensor unit passes through the tubing to the indoor evaporator coil where it is expanded in the coil, removing the heat from the airflow passing over it, then passes back at low pressure to the compressor to be recompressed - so has to be only one or the other refrigerant in the entire A/C system.

I would guess that the indoor (evaporator) coil corroded out and was replaced at some time (soudns like Dec 2014), possibly using an original equipment manufacturer's coil that was rated for both R-410a and R-22 (R-410a runs at higher pressures so could also handle the R-22 system pressures if rated for the needed cooling capacity with that gas) and the R-410a tag was not removed from it - or it was replaced with a coil for R-410a units which might or might not be a compatible coil. It is possible that say a R-410a coil for a different capacity system would have also fit your system with R-22 - I have seen replacement coils with a dozen or more ratings on them, for a variety of refrigerants which might be used in them. Also, even though it is illegal to put in a mismatched coil (one not rated for that gas and refrigerant flow rate and cooling capacity), some installers will do it anyway.

The refrigerant can be tested to see if it is R-410a or R-22 (or possibly if it has been mixed over the years because of the mismatched labels) but I would imagine that would run a couple hundred dollars and could be a real hassle because it would have to be shipped for testing in a pressurized container, and probably also as a flammable gas not knowing exactly which refrigerant is in it. In a large city the major HVAC gas distributors (like Liquid Air or Airgas or Honeywell or such) might be able to test a bottled atmospheric-pressure sample - your HVAC tech would have to call around to see who can test it and how to get it to them. If it turned out the wrong gas or that mixed gases were used, either you would have to cross your fingers about compressor life (assuming it is cooling adequately at this time) or the system would have to be flushed to remove the gas and lubricant (the lubricants for those two gases generally have different chemical bases so are not at all compatible) and put in new gas - which given the variations in R-22 gas charges these days might run from around $350-500 for a smaller system and reasonable gas pricing, to as much as $500-1000 range for a larger system (say over about 4 tons capacity) or from a vendor who is price gouging on R-22. So both alternatives have a substantial $ involved.

Can you possibly find out who replaced the indoor coil and ask that vendor to check their invoices for what was done (especially since you have the month, year, and address and presumably previous owner's name as well) and whether that unit is cross-rated for both gases, and if it is a compatible sized coil for that outdoor unit. Also if their records show what gas was put in the system after the coil swapout.

If you are very lucky, you might find a tag on the coil with its manufacturer and part number and be able to find out from the manufacturer if that coil is compatible with R-22 (since that is what is on the compressor) or not, and its heat transfer rating with R-22.

If it turns out to not be compatible (according to manufacturer rating charts) or the gas is wrong (which if R-410a in an R-22 unit would mean the efficiency would be WAYYYY down and the unit would be long-cycling trying to get the cooling job done when it is hot because it would not be pressuring the gas up enough to operate efficiently), then you have a tough decision unless you could convince the company who changed it out in 2004 to make it right at no charge. That is pretty unlikely, especially as I think the applicable EPA regulations prohibiting incompatible component installation post-date that installation date.

Your tough decision would be whether to change to the correct gas if the wrong one is in there (for a pricey changeout), change the coil to correct sized on if that one is not a match (typically $1000-2000 range including coil and installation), or say a 13 year old unit is nearing its design life and put the money into a new, higher efficiency unit instead. Personally, for that age unit (assuming a normal efficiency, typical residential unit), if it is operating OK now I would cross my fingers (unless loss of cooling would be hazardous because of a resident's health condition), have any minor leak repaired and topped off if needed with R-22 (if the tech was there because it is low on gas), and hope it lasts another few years - and start budgeting for a new unit in the next 2-5 years.

By temperature measurements on the evaporator coil and checking the operating pressures, he should be able to tell you if it appears to be working pretty much normally, or is running at very low efficiency due the wrong gas likely being in it - because if the wrong gas is in it, based on the operating pressures and the line and coil temps when running, he should be able to tell if it is operatings anywhere near its design operational parameters.

Answered 1 year ago by LCD

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