I have had a repair man out 4 times and he says he can't find anything wrong with the unit. I cannot even feel air coming out of the diffusers unless I climb on a chair and put my hand right next to them. The A/C runs non-stop when it's hot. It will run for 5-6 hours and shut off while the temp in the house is 79 and the thermostat is set at 74. What could be causing this? We have had coolant added. The a/c man says the coils are clean. I can feel air being drawn into the unit at the intake.
Here are some things that you can do:
Here is what I would recommend to have a professional do
Get a second opinion
The issue should have been resolved by a professional within 2 visits. If it takes more than that, you need a fresh pair of eyes to look and re-assess the problem(s) with the unit. Even if you need to pay an additional fee with someone else, it might be worth it to get the correct resolution.
If the unit is under warranty, you can request from the company responsible to send a different technician for a second opinion at no charge.
The lack of airflow makes me suspect that the coils are icing over, clogged filter, or a disconnected duct line inside the wall/floor. If the problem only happens on the warmest days, and you get good airflow any other day, then your coils are icing over. The system needs time to defrost, could be oversized for your home, and you may have a clogged filter contributing to the issue. A clogged filter is easy enough to determine by pulling out the filter and checking it for dust buildup, and if it is covered then just replace it.
A disconnected duct line will always result in lower airflow. If the ducts were cleaned, it's possible the cleaning coming knocked something lose while pushing their tools through the ducts. If this happens, you may have cold air getting blown out behind the thermostat causing it to get a false reading.
Another possibility is a damper that's closed (this might appear as a small lever on the outside of a duct line coming off the HVAC). Make sure these are parallel to the duct.
Since this is a problem on the warmest days, one final possibility is that you don't have enough insulation and/or the HVAC system is undersized for your home.
I would think since the unit checked out fine, then it could be the thermostat that may need to be replaced. Is the unit sized right for the square footage that it is cooling? Plus, I would say that the leaves and debris are not helping the unit to run effectively. I had to have my thermostat replaced when it behaved in that manner and all else checked out fine.