re: New AC running much longer than old one

I promise you it is.

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So what could the problem be to cause this?

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Well with a low temp split (say 14 F), with temps measured inside the return & supply plenums, normally it would be a refrigerant issue - undercharged or overcharged - but the tech is saying that’s OK?

A certain amount of duct leakage is acceptable - 3% would be - but is this a wild arse guess on his part as there a procedure for measuring duct leakage which involves the use of the same equipment as a blower door test (house air leakage test), covering the supply registers & pressurizing the ducts, and leakage is calculated, and problem areas indentified with smoke pen or thermal imager. I had it done on my ducts a couple years prior to my changeout. And leakage is not just checked on the supply side - it needs to be checked on the return side - if hot air from the attic is being pulled into the return plenum side b/c of leak there then that would cause comfort - run time issues as well.

How is the humidity in the house with the new system? Typically the blower speed in the furnace (do you have a gas furnace?) comes set at a factory default highest speed of 400 cfm per ton. It’s better to have the blower set at slightly lower speed in our hot, humid environment, 350 cfm per ton, so return air from inside the house stays in contact with the cold evap coil longer, increasing the temperature split and lowering humidity. Often blower speed is not changed by the techs from the factory default highest blower speed with a new install.

Lastly, is this fairly large HVAC company? If so, you can request a senior tech to come out to discuss your concerns, and check things. Most the young guys do the installs and senior techs handle problem issues-repairs, and though the young guys may be competent, they aren’t as experienced in tweaking systems, finding issues, etc as the old techs.

I had a change out last year, same size system (4 tons, single stage, R-22 to R-410A, SEER 12 to SEER2 15). I’m getting as good or better comfort than the old system. I can’t comment on my utility bills - I’m on levelized billing - but they not higher than before the changeout. I did have a second return duct installed on the opposite side of the house, as my original return plenum was a 1/3 undersized, and that has definitely improved comfort issues on the other side of the house where the new return plenum was added.

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It’s better to have the blower set at slightly lower speed in our hot, humid environment, 350 cfm per ton, so return air from inside the house stays in contact with the cold evap coil longer, increasing the temperature split and lowering humidity.

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Is that something I can do myself or do I need a tech for it? It's a small hvac company that did the work so they don't have any senior or non-senior techs - just the owner and two guys who work for him. Came recommended by my dad who has used this company for years with no issues. I'm pissed and feel like he fricked me sideways somehow.

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HVAc industry gets the majority of its revenue from uneducated owners by selling them oversized units. It is crazy.

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I have the same sized unit as before and didn't have this issue before.

Does your new unit have a humidity setting? If so, it could be running longer to reduce humidity in your home. Adjust the humidity setting up and that will allow for a shorter run time.

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I have the same sized unit as before and didn't have this issue before.

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That comment wasn't about your new one. Both old and new were severely oversized IF your claim was indeed true. 50% duty cycle/loading in 100F heat is asinine.

I got up there this evening and turns out there were significantly more air leaks than I realized. No way in hell I only had 3% air leaks - that was bullshite. I sealed them all off with reflective tape and then painted duct sealant over all the areas. I also replaced the thermostat. Hopefully this helps. I’ll see how long it runs overnight and compare.

I just felt with my hand. It was easy to do since my attic was 273 degrees

If it's set at 69 then it will run until it's 69 then stop for 8-15 minutes. Then runs again for 15 minutes even though the temp is still 69 and will stop for 15 minutes. The cycle repeats itself continuously even with the temp staying at 69 degrees. Of course, it stays at 69 because it's trying to KEEP it there but why won't it come on only if the temp rises to 70 instead? My only option is to turn the entire unit off once my indoor temp reaches the desired temp and then turn it back on once it rises again. That's going to be exhausting and probably not good for the unit. My guy is coming back out tomorrow to look at it and I'm not letting him leave until the problem is identified. This is ridiculous and unacceptable to me.

What thermostat are you using? My Sensi Touch had a setting where I can adjust cycle times. Mine would do the same as yours, constantly kicking on and off. I changed the cycle settings and it seems to have gotten better.