Evaporator coil needs replacing?

Over the last 2 or 3 summers I've had to have the HVAC tech come out once the temp starts to climb, to re-charge the upstairs a/c with Freon (Trane XE1000, 10 yr old unit). Obviously a leak, but cheaper to re-charge than to fix. Since last summer the Freon charge didn't last the season, I've bit the bullet and decided to repair the leak.
Tech came out and said the evaporator coil was corroded and was causing the leak. The slow degradation of cooling power (versus sudden loss) was indicatory of a bad evaporator coil, plus he visually observed corrosion.
Cost (parts, labor, installation) was $825. This seems high but wanted to check to see if in fact it is.
Also, was told two things can cause corrosion of coil:
1) Running a/c at low outside temperatures. I don't do this but am the second owner of the home so don't know what the previous owner did.
2) Dirty filters. I change them pretty regularly, every 45 to 60 days. Again, don't know what first owner of the home did.
Will running the fan constantly help in case any ice does form on the evaporator coil? I usually run the fan 24/7 to help distribute the air more evenly.
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good filter.

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This is a lay-person's opinion.
Depending on where you are the price may be really fair. I paid $600 last year and we are not in a high cost area. I was hot enough that it seemed like a bargain. It was not my high estimate.
The crap they use to make the coils is caustic. A manufacturing failure to properly clean the coil can lead to failure. Moisture inside the system leads to premature failure. Make sure that the price you are paying includes a new "filter/dryer". I have two units one failed after 7 years and the other worked on Saturday. 12 years old this past month.
Running the unit at OS temps below the recommendation can cause problems. EV coil failure is not one of them. RTFM. And in most cases if it is cool enough outside to cause problems the unit won't be running anyway.
Filter don't have a d%$# thing to do with it. Ice on the outside of the coils is a different problem. Keeping clean filters and good air flow does help with this. It is the moisture on the inside of the coils that cause the failure. The outside of the coils almost always are wet. That is why the unit drips water to the drain.
In all fairness to the tech. He felt a need to answer your questions and gave you the BS he had been programmed to say.
Get a couple of more estimates to be sure that you are getting the best price.
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DesignGuy wrote:

one of the major components of the system after only 10 years on the conjecture that some corrosion he sees might be the problem?
I'd get a second opinion.
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Surface corrosion does not necessarily mean a leak. Did he use a leak detector? Did he pinpoint the actual leak? Was it a joint or the tubing?

Not that high for a job done right

Never hear dof all of that. Corrosion is a chemical reaction. Icing may cause some moisture to helpt it along, but I have my doubt.
I'd get a different tech out for an oinion.
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DesignGuy writes:

You can find marked-up prices for parts at grainger.com.
Your tech is grossing about $500 profit for himself or his boss.

Research "formicary corrosion".
Failures in the 5-year and up ages are surprisingly common. It's not your fault.
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Did you add in licensing, insurance, consumables, time, etc? Sure he made some money, but not $500.00...
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HeatMan wrote:

What part of "grossing" did you not understand?
Pete C.
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I understand Gross profit, but how do YOU come by that? Just the coil price or all material used in the changeout?
FWIW, I'm done. I do not have to justify my pricing to anyone on the 'net.
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wrote:

The whole thing. "Grossing" didn't register. I thought he meant "grousing".

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Tech came out and said the evaporator coil was corroded and was causing the leak. CY: Didn't he use a beeper? You mean he just looked at it and then guessed?
The slow degradation of cooling power (versus sudden loss) was indicatory of a bad evaporator coil, plus he visually observed corrosion. CY: Actually, it's a sign of a slow leak increasing to a moderate leak. That leak could be in any of several places in the system. So replacing the evaporator doesn't guarantee a fix. The leak may be some where else.
Cost (parts, labor, installation) was $825. This seems high but wanted to check to see if in fact it is. CY: Of course, we don't know if the evaporator is in the cellar, or attic, or how easy it is to service. But from what I know of evaporators (have installed several) it sounds high.
Also, was told two things can cause corrosion of coil:
1) Running a/c at low outside temperatures. I don't do this but am the second owner of the home so don't know what the previous owner did. CY: Could contribute to icing, but don't know that it promotes corrosion.
2) Dirty filters. I change them pretty regularly, every 45 to 60 days. Again, don't know what first owner of the home did. CY: A dirty filter is the one which is working. A clean filter is something to be worried, cause all the dirt is going right through. Of coruse, dirt clogging the evaporator might be corrosive.
Will running the fan constantly help in case any ice does form on the evaporator coil? I usually run the fan 24/7 to help distribute the air more evenly. CY: Yes, running the fan full time I think it's a good idea. Sounds like time to get a second opinion. Sounds like you need a tech with a leak detector beeper to see where the leak really is.
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