A week ago I had my 15 year old Carrier heat pump replaced with an Infinity heat pump (3 ton, 15 SEER).

I have the controller programmed for two time periods.

6 am- 78°
9 pm- 72°

Since a day or so after installation, early evening about 7 pm or so the "Cool At" temperature, which is the target setpoint, changes itself from 78° to some other number. I have seen it at 74°, 75°, 76°, and 77°. When I look at the program, the set point is still 78°.

On Tuesday I called the contractor. That afternoon they sent out a young man to look at the controller, and he could not find anything wrong. It happened again Tuesday evening and again last night. I called this morning and they sent out the man that installed the system (they have very responsive service, I am very pleased).

He spent about 30 minutes playing with the controller, making calls to his office, reading my manual, going to his truck, etc. Eventually he told me that the controller was acting normally, in that it was anticipating the 72° requirement at 9 pm. He told me that the system wanted to already be at the desired temperature at the time it was programmed for. Therefore, it started cooling down before 9 pm so that at 9 pm it was at 72°.

I have never heard of a system working like that, so I am somewhat skeptical. Is what he told me accurate?

If so, can I override that part of the system? We don't want the temperature to cool off before 9 pm. Should I set the time back to say, 11 pm, so that it starts cooling down later.

As always, thank you in advance for your assistance.

Chris Smith