Just had a Rheem 12 SEER, RPMD 3 ton heatpump with Rheem air handler RBHC17J11SHH, RCHA36A2G coil installed. This repalced a Heil 3 ton unit manufactured in 1993. Previous unit was able to maintain 73 degree setpoint on 95 degree day and occaisionally cycle off. New unit ran for 8 hours straight yesterday maintaing house temp. of 75 degrees(set point 73)before it finally managed to attain set point and cycle off. I'm located in central South Carolina and temperature yesterday was 95 degrees and humid.

I'm calling the contractor to check out the unit but would appreciate some insight. By reading one of the previous posters who has a similar problem I understand some of the things the contractor should be looking for. I am however curious to get your opinions on the following:

During the morning when the outside temperature is 80 degrees or so the temperature from the register nearest the airhandler is 56-57 degrees or so. Measuring my return temperature nearest the central return grill the return air is about 74-75 degrees. The delta seems very good to me.

During the afternoon when the unit cant meet set point(73) and is keeping the house at 75 degrees the return temperature is about 76-77 but that same register is only providing 68 degree air.

The house has a west orientation and therefore gets the direct blast of the sun in the afternoon. Attic temperature hasn't been measured but its hot as hell up there. There have been no changes to the house at all other than the new system.

Hopefully the contractor will have a fix. I'm assuming the best time to have him check the units would be mid afternoon when they are unable to keep up.

Lastly, it was my understanding that in this area design temperature was 75 degrees on a 95 degree day. Is that correct. Again unit I replaced easily maintained set point of 73 on 95+ degree day and did cycle off and on. Is there a difference between 3 tons in 1993 and 3 tons today?