So this is a follow-up to my previous AC tech horror story: Rust on outdoor ac fan motor? Tech recommends replacement? . I got a new AC tech from a small two-tech company with glowing reviews, hoping for a better experience.

One of my two AC units was not cooling well. The temp drop across the evaporator coils was only 12 degrees, and by the time the company came out a few days later, had fallen to about 5 degrees. (Air in 77F, air out 72F.)

The tech (who also owns the business) checked refrigerant pressure and checked for leaks at the outdoor unit. He found pressure about 30psi under what it should be and no leaks. I understand that getting access to the indoor unit's evaporator coil is labor intensive. Based on unit age (10 years) and lack of outdoor leaks, he is confident it is a leak in the evaporator coil and recommends replacing.

Is this a reasonable course of action? Should the actual source of the leak be identified before proceeding, or is it reasonable to assume it is the evaporator coil?

  • 2
    Before doing anything else I would recommend a 2nd pressure test a few days later. If it is still at 30 psi there is no leak...
    – Tonny
    Commented Jun 23, 2022 at 14:34
  • Where are you at that life expectancy of an evaporator is 10 years. I believe they have "sniffers" that can find the leak so I would want them to pinpoint the leak. Commented Jun 23, 2022 at 14:42
  • I would have him look for the leak indoors before replacing. Ask him to show up with all the parts necessary for the replacement if necessary, but ensure the leak is in the evap coil before just blindly replacing it.
    – FreeMan
    Commented Jun 23, 2022 at 14:48
  • 1
    @Tonny depends on how slow the leak is, if it took a year to drop from normal to 30 psi below spec then 2 measurements a week apart will the same within rounding error Commented Jun 23, 2022 at 15:26
  • 1
    @tony an hvac system pressure is temperature dependent. Refrigerants change pressure more than a other gasses the pressure could be higher the next time or lower with the same outside temp if inside the home is warmer or cooler. Pressure alone is not reliable. Pressures and temperatures are needed to calculate super heat and sub cooling. Don’t get scammed on a pressure only reading.
    – Ed Beal
    Commented Jul 24, 2022 at 14:43

2 Answers 2


Many, many, years ago when I was still a young man we had what I called "parts changers". If they could not pinpoint the actual cause of the problem they just changed parts until they found the bad or worn out part. You haven't said that he has found the precise location of the supposed leak, so why are you listening to him when he suggests changing the indoor coil.If that does not fix the problem what is the next part to change. So, before you start to change parts on an assumption, how about telling these "experts" to first find the Damn leak.I am surprised by how little knowledge the tech experts have of the equipment that they claim to know how to fix. In my day, I would find the leak or other problem and fix it. my 2 cents

  • I call it shotgun repairs don’t focus on anything just change something, I doubt there is a detectable leak, it just reached the point where there is not enough refrigerant to cool efficiency. But I agree+
    – Ed Beal
    Commented Jul 24, 2022 at 14:52

Your 2 cents is straight up common sense!

Your area is full of scammers!

10 years having a recharge is not out of the norm where even a high end tester like my Dtech select will not find a leak.

At 10 years old it should be a unit with 410 or another refrigerant that is still available.

Saying there is a leak at the evaporator when they can not find one is total B.S.

adding a couple of lbs of refrigerant it will be fine for another 10 years in most cases or until something really fails. Like the capacitor or contactor which do wear out.

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