Help! - I need help - I recently had central air conditioning inst...

HOMEOWNER CRIES FOR HELP...

posted: September 8th, 2008 - 2:04pm

QUESTION:
I need help - I recently had central air conditioning installed and am not sure it is functioning correctly. What I noticed initially was that there was very little air movement in the house and it did not cool well. The HVAC company felt the unit was sized appropriately and added a large return duct to move more air into the system since they said the coils were freezing? and not allowing for adequate heat exchange (the old return seemed to run between some studs and was narrow). Since this change there seems to be more air movement and the return air feels cooler. Measurements between the duct return and air coming out from the vent show a 20 degree difference.
What I have noticed, however, is that on a hot day (where the temperature is around 90 degrees with a lot of humidity) the unit will drop the house temperature in the morning from 80 to 75 degrees (when the outside temperature is around 76), but as the day warms up and the outside temperature goes to 90, the inside temperature seems to increase slightly as well and might fluctuate between 76-78. Is this typical that the house would warm up during the day even though the air conditioner is on non-stop? The house feels comfortable inside but the unit stays on practically non-stop and seems to have difficulty dropping the temperature further.
A manual J calculation was originally done but the HVAC company (and rechecked a few times) which suggested that a 2.5 ton unit would be sufficient when there was originally a 3 ton unit - so one of my questions is whether this might be a problem. Am I crazy or is this unit functioning correctly? Thanks

ANSWER: The unit is functioning correctly if your temperature readings are accurate, 20 degrees is about perfect but obviously there is either a sizing issue or the air is being improperly distributed accounting for the long run time. Is there any way you can change the heat infiltration (seal windows or pull down shades on the appropriate sides of the house at certain times of the day).
It is possible to be a little undersized and be able to change a few things and make it through the hottest times.