There should be air flow adjustments on the ducts under the house. Maybe some are shut back a bit for a reason. A good HVAC company, can check that out for you.

Crawl space is just that. Requires army crawl. AND HVAC company charges a $150 trip charge just to roll into the driveway.

Duct cleaning should be an absolute last resort. Mostly they accomplish nothing. And in some cases, they can actually damage the ductwork (flex ducts, internally insulated ducts, box ducts).

OK - No duct cleaning for now. Still have issues.

We moved in on May 9, 2022. New A/C was installed in March 2022. Home inspector said all ductwork was connected. Only issue was one run had some loose insulation.

A manager from the company that installed the A/C spent 2 hours testing/adjusting the unit. He said it had full charge of freon. He tried changing fan speed and balancing. He could never get any improvement of the 11 degrees differential between return air and output air (unit ran for nearly an hour). No matter how much the unit runs, the humidity never falls below 70% (outdoor humidity between 40-50%).

Does anybody have any suggestions as to what else might be check/tested?

As sktn77a said,

As EPA says about Duct Cleaning - Likely a Waste of Money

Hi, Keith,

As a rule of thumb, the temperature differential across the evaporator coil should be around 20F. It may be that some portion of the HVAC system is undersized for the cooling load. You might ask the HVAC contractor for a copy of the heating/cooling load calculations used as the basis for sizing the equipment and go from there.

Here are the air flow readings I observed:

HVAC contractor has been "way" less than helpful. Said they sold & installed the unit at cost as a favor for the previous owner (so I doubt any sizing calcs were done). Whined about having "no money" in the unit. Even though it is still under warranty, it took 3 phone calls just to get them to come and check the unit. I doubt they will be much help in the future.

The house is only 2,747 sq. ft. I don't know why 2 ACs were installed. (Old unit was abandoned and is still in the attic).

Since the work was performed for someone else, the HVAC contractor may not have any warranty obligation, but I suggest you check with your state's contractor board or equivalent to see if that's indeed the case. A new system should perform as designed. I suspect what you have wasn't.

"Even though it is still under warranty, it took 3 phone calls just to get them to come and check the unit. I doubt they will be much help in the future."

The unit "may" be warrantied but the installation warranty is not technically yours. They really owe you nothing.

The house was listed and sold as having a "new HVAC under warranty". Therefore, they, or the owner, most assuredly do owe me any required repair or maintenance during the warranty period! For, every house we have sold or purchased in the past, major system warranties transfer to the new owner.

Hi, Keith,

You might want to check with your Realtor or attorney regarding the transfer of any warranties at the time of sale. Most manufacturers have a defined process for transferring warranties from one owner to another. There is usually paperwork and a cost associated with the transfer.