We just had a carrier seer 15 central ac/heating installed in November 07. I live in houston, texas if that makes any difference. Our house is 1710 SF

Our electric bill last month was almost $500.00. The unit is off during the day as we both work but when we are home we have to run the heater at 78 just to keep the house warm. It is always colder in the house than it is outside. It hasn't seemed to be right since it was installed. I have had the company that installed the unit out quite a few times and they say everything is fine.

Anyone have any suggestions as to what might be wrong? Also is there a way to check and make sure the thermostat is working correctly?

Thanks in advance!