Leaking evaporator coil

I got a tech out to do a leak search on my circa-2000 R-410a system (have needed 2 recharges this summer) and he detected a leak in the evaporator coil (he was using some Johnson Controls sniffer).
The coil was labeled with some application labels and one line read "Refrigerent: R22". I asked the tech about it and he said he didn't think it was right; after a couple of calls, there was some difference of opinion among his supervisors about whether it should be replaced at no cost because it was the wrong part.
One of the tech's supervisors said there's a regulator fitting just in front of the supply side of the coil that could be swapped out, making the coil suitable for use with R-410a. Another reference said that this coil was pressure-tested for R-410a pressures and should be OK (I think the pressure testing number on the coil label was 450psi).
Is it possible to make a valid case that some corner was cut and an inappropriate or inferior part was used when the system was installed? Or are they right and the coil was an acceptable part when installed?
I'm ever-so-slightly out of warranty, and if there's a reasonable argument to made that a bad/wrong/less-than-durable part was used in place of a more technically correct or durable part, it'd probably not cost me anything or just some percentage of the replacement coil price.
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The correct coil should have been installed in the first place... and there are a couple of manufacturers that have had a problem with leaky coils... Carrier comes to mind........
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Since I'm a data networking guy and not an HVAC guy, can you explain why the R22 coil was a wrong part? Is it merely operating pressure, or is the gas somehow corrosive/reactive to joints or some other reason beyond "it's the wrong part" -- it's pretty easy for them to say "with a flux capacitor, it works with R-410a" or "it's pressure tested to R410-a levels".
I don't necessarily need to be an expert, but I need to at least sound as if I know enough about why it was the wrong part that they're better off arguing with someone else.
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Alot of manufacturers are going to a single coil for R22 and R410A. The coils should have no problem handling either pressure. They are doing this to reduce warehouse space since the inception of 13 SEER and the extra space requirements for the same # of units. When you order a coil, you will order a coil and a matching TXV for your application.
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Bob Pietrangelo
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If is leak in the system it should have been fix at first service call Question can it be fix!! warrantee should be in affect at first service call?

That is good question, also if part is incorrect then your SEER is derated
> One of the tech's supervisors said there's a regulator fitting just in front

450 PSI is standard pressure testing for old Refrigerants for R-410 I could not say however your cooling coil while unit is running will be operating around 110Psi. head pressure depend on several things which I would not speculate.

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