Getting callbacks on Long Island AC systems that cooled fine in spring but can't keep up now, what are we missing?

[All Shore Plumbing NY]

Systems are maintained, refrigerant checks out, filters clean. But once Long Island hits a stretch of 95+ degree days these older central AC systems just can't hold temperature. Homeowners are calling back saying the AC repair didn't fix the problem. Starting to think it's duct leakage or load calculation issues on these older homes rather than the equipment itself.
Anyone else seeing this pattern this summer?

 

[Sylvan]

How old is the system? Are the coils dirty?

I was a stationary engineer at 90 Church Street in Manhattan(central absorption system), and sometimes I had to service smaller systems.

The coils were blocked with feathers, leaves, grease, and dead bugs

 

[Sponsor]

 

[Fitter30]

Look at the blower wheel are the cupped blades dirty? If its dirty pull blower remove motor take housing outside and with dish soap and garden hose clean it. If they are the coil is to. Whats the temp difference across the evap? Return air at filter and discharge 16" -18" from coil. Should 18°- 22°. Expansion valve , cap tube or orfice ? Suction line ice cold? Type of refrigerant and pressures?

 

[RetiredInGueydan]

Systems are maintained, refrigerant checks out, filters clean. But once Long Island hits a stretch of 95+ degree days these older central AC systems just can't hold temperature. Homeowners are calling back saying the AC repair didn't fix the problem. Starting to think it's duct leakage or load calculation issues on these older homes rather than the equipment itself.
Anyone else seeing this pattern this summer?

A properly functioning system that can't maintain temperature in those conditions was undersized at installation.

 

[Fitter30]

Nassau county ac design temp is 88° @ Republic New York for Manual J
With indoor temp of 75% @ 50% rh
Need to contact your electric provider see if they offer a energy audit that includes a blower door test ( sees how tight the house is). Have windows that haven't been replace or reweather stripped. Cheap thermopane windows that seal failed. Doors the same way. Caulking not up pare.