That was surreal... "It's official: I know nothing about HVAC" - HVAC engineer

I have a big problem with my air conditioning not keeping up in my condominium. Outdoor unit is a Tempstar 2.5 ton 12 seer, indoor unit is a Goodman GMP075-3. Stat is at 68. If the outdoor temp stays below 75, indoor temp stays around 68-72. If the outdoor temp is above 75, the indoor temp rises, faster or slower depending on the outside temp. If we get a heat wave and it's above 90, the inside temp will rise to 80 and stay there until the outside temp falls below 75.
Called the company that replaced the company that installed the systems when the condo was built. A tech came and looked out the outdoor unit... good pressure, no leaks, working great. They looked at the indoor unit... everything looks good. They can't figure it out. The think there may be issues with the thermostat, so they start by replacing it. After several days, it makes no difference.
The owner then came out. Came to the same conclusions, the indoor and outdoor are working good. He said that the original company that installed the ductwork made it a bit more complicated than it should be, and basically the air has to travel farther. Due to some complaints from other residents, the builder asked this new company to come up with a better ductwork design. They now do it a lot different than the previous company. He says he feels that replacing the air handler (the Goodman GMP075-3 is a forced air furnace with a 1/3 HP blower motor) with a higher efficiency unit with a DC Drive motor will overcome the ductwork issues. However, when checking all the registers, he was very surprised to find good flow out of all of them.
He was at a complete loss. He said he wanted to call in a engineering team.
Three guys came out, one was the boss. He looked at everything. The outdoor unit is in top shape. The air handler has 71 degrees from the return air, and 51 degrees from the outgoing air. He says he normally expects to see a best case scenario of a 16 degree drop. I'm getting 20, which he says is a "pipe dream." He then checked the air flow through the unit. It was more than optimal. He checked air flow out of all the registers, taking the size of the condo into consideration, it was again more than optimal. The temperature out of the registers was about 60 degrees. He ruled out any open headers in the ducts, as the flow out of every register--even the ones farthest from the air handler--was good.
Yet, the day the team took all these readings, it was 70 degrees outside, and still 75 degrees inside (it was 93 degrees the previous day and the temperature was still slooowly falling inside.)
He checked the insulation in the house. It was perfect. Which didn't surprise me... I hardly ever have to turn my heat on in the winter, the condo insulates so well.
He spent a good hour scratching his head. He left saying, "this is the first time in my 22 years as an engineer that I've seen anything like this. You have a system that is above optimal. If it's 90 degrees outside, your system should drop your inside temp down to 70 quite quickly with no issues. Yet right now, every aspect of the system is working more than perfectly, and it's colder outside than it is in your house. It's official... I now know nothing about HVAC." He said he is going to have to do an intensive case study to figure out what the hell is going on.
About 12 hours after he's gone, it's now 60 degrees outside and still 71 degrees inside (again the stat is at 68).
Has anyone ever heard of a similar story?
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Suggest they clean the condensor.
--

Christopher A. Young
You can\'t shout down a troll.
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Yup... whenever the home owner tries to get the system to turn the home into a walk-in freeze box. The *normal* system design temps are to *MAINTAIN* 75 degrees inside in cooling mode and to *MAINTAIN* 72 degrees in heat mode. Leave your thermostat at 75 and watch the system hold 75 degrees even when its warm out, and watch your utility bills go way down. FWIW, I am real surprised that your not freezing your evap coil.
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Its almost always the thermostat. Bubba
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Let me say this to you I am not AC guy as some people here already know that, however I am refrigeration tech. You did not gave us size of your condominium it is impossible even to guess, what your problem could be but if I am to guess, it looks like that you have miss match condenser to cooling coil. Coil oversized for size of condenser or perhaps compressor is not doing what it suppose to (not pumping to full capacity "most likely") it need to be replace or and perhaps even grossly overcharge. Get mechanic that knows what is looking at and not one that is guessing or some one is given you a snow job Good luck from DIDO www.cas-environ.com

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