The AC Can't Keep Up in 92 Degree Heat

The summer started and the temperatures rose into the lower 90's.  We wanted to save on energy costs, so we turned our ACs to a very warm 79 or 80 degrees.  In the afternoons, it was the hottest time of the day and we noticed that the ACs couldn't even cool the house down to 82 degrees.  The units were running non-stop and could not even bring the temperature down to 82 degrees until night time.  The outdoor high temperatures were about 92 degrees each day, so our AC system couldn't even bring the temperatures down 10 degrees in the house.

This was very alarming.  We just paid for two brand new central heat and AC systems, and we are still going to have to use window AC units to cool our house!?!  Something must be wrong.  We have very large AC units for the square footage of our house, so the size of the units should be more than enough to cool the house.  Once again, we went into the attic to investigate the problem.  It turned out that the many of the supply duct joints were taped instead of being sealed with mastic and the tape popped off.  The ducts were leaking cold air all over the attic.  This was again a problem related to incorrect installation.

We also noticed that the return vent for the smaller HVAC unit was larger than the return vent for the larger HVAC unit.  This did not make sense, since the size of the return vent must be proportionally sized to the size of the HVAC unit.  When we asked the owner of the HVAC company about that, he told us not to worry about it because it was good enough. 

We decided to research the size of the return vents and ducts on the internet to see what the manufacturer of our HVAC units requires.  We learned that the smaller HVAC unit's vent and duct was a little too small for the size of the HVAC unit, but it was close so we decide to let that go.  However, the size of the larger HVAC unit's return vent and duct was way too small.  We also learned from our research that having a return vent/duct that is too small causes poor airflow from the supply vents and poor efficiency.  This could be another reason why our AC could not cool effectively.


We called the HVAC company to let them know we need another return vent/duct for the larger unit, and we need the supply ducts in the attic sealed correctly so they don't pop open again.  The owner of the company became outraged with us and told us we were wrong about the size of the return vent/duct.  He also insinuated we were unreasonable with our requests for these repairs.  After cooling down and making some phone calls, he finally agreed to do the work.  He proposed a location for the new return duct/vent which would make the length of the return duct about 60 feet long.  We asked if the return would be effective with such a long run because it seemed like it would lose suction, but he told us its fine.

He promised to do the work the next week; however, the workers never showed up.  So hopefully, they will complete it the week after that.