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Question DetailsAsked on 7/24/2017

do you have to replace all the freon when you replace evaporator coil

one HVAC man said we only need to add 4 pounds of freon on (R22) Other guy said we have to replace all the freon ..over 14 lbs

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1 Answer


Depends on the contractor philosophy (some will not reuse refrigerant in any case - always ship it off for recycling) and the condition of the lubricant in the existing refrigerant (it circulates the compressor lubricant with the gas).

It IS legal to reinject the old gas - though I have seen a few newer machines/parts where the warranty is voided if that is done, so that issue may answer the question for you if you read the new coil and the original system warranty (if original system is still under warranty).

Some contractors will extract the existing gas (that is required by law - cannot just vent it) then reinject it after the repair, topping off with new gas as needed. Personally, I would never do this without checking the filter/drier (after the gas is removed) to see if the existing lubricant is clean. If it shows signs of scorching or burning or sludging (due to low refrigerant overheating the compressor, or due to water or mixture of incompatible lubricants in the gas) I definitely would NOT reuse it.

Also, if the contractor does not thoroughly clean the extraction machine, you run a significant risk of contamination (potentially major) from the other lubricants in the machine. Basically, these days (with over a dozen different types of incompatible lubricants in the various gases) and with a dozen or so different gases in common use, unless he has a separate machine for each type of gas and lubricant (VERY unlikely, since they run $500-1000 apiece for a small one and more like $3000-5000 for a larger commercial-grade one), I would not risk it. Some of the larger machines remove ALL the lubricant - passing only the gas through, which with good quality filters frequently changed might remove much of the lubricant concern, but does not eliminate the issue of possible mixing of gases in the machine if previously used for another type of gas, or of your system possibly having had different gases put into it in prior topping off cycles, if any.

Used to be, when basically almost all residential systems were R-22 (Freon), I said reuse was OK if the filter was clean and the extraction machine had a high-grade filter in the system - but with all the different refrigerants and lubricants (and maybe not knowing what has been put in your system in the past - you may already have a mixture of two or more gases or lubricants, a bad thing) I no longer recommend in-place recycling of the gas - even though it may run typically about $500-1000 range for the additional 10# or so of gas you need.

[BTW - if the filter/drier or tubing shows blackening or sludging, the entire system should be chemically flushed out before putting in the new coil and gas]

Of course, when you add $1000-2000 for a new coil (depending on locale, model, if OEM coil or aftermarket, and amount of gas needed) replacing a coil or compressor generally (at least if the part is not under warranty or system is over about 7-10 years old) legitimately brings up the issue of repair versus replace. You can find a number of previous questions with answers and thoughts on the economics and decision-making factors of that in the Home > HVAC link, under Browse Projects, at lower left.

Answered 3 years ago by LCD

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