I had a new furnace and central air system installed. I had an old condenser that I took from another house. The installer told me that it was probably to small for my house but did not tell me what that meant. I had it put in since I didn't have the money for a new one at this time. My question is , I am having trouble staying at my desired temp when the days are really hot, is it because the condenser is to small and will a newer bigger more efficient one be the answer. My furnace is a little bigger then you would need for my size house because I am planning an addition, so I don't think that the furnace is to small. I also let the air run threw the evening to get me at my desired temp. but it will slowly lose ground during the day to the hotter air outside and is running constantly. Any help would be appreciated

I`m sure the installer probably knew it when he told you it was to small, he probably thought when he told you and you didn`t ask questions that you understood. So in all liklyhood you now have a condenser that can`t do the job it takes for your home,, happens sometime when we try to cut corners and pinch pennies

Wait till you get the electric bill with a ac that runs all the time

For the proper equipment size a manual J will need to be done on your home since all other forms of calculation do not work well.