On 8/15/2017 11:56 AM, JR wrote:
We have a new Carrier furnace/AC & Touch & Go thermostat.

1) The AC keeps running past the setpoint but only shows the setpoint as Actual temp. Set=73 Actual=73 but real temp is 71. 1st repairman said it was normal to run 3 hours for 1 degree & be 2 degrees colder than setpoint & this is how new ac works. Told him I set U2 backlight to OFF & U4 program to NP. Still told me nothing wrong. 2nd repairman replaced thermostat & it worked. That was until I set the Advanced Settings U2 backlight to OFF, that makes the AC run on. So I turned the U2 backlight back to ON & now it stops at set temp. Why is the backlight controlling the AC shutoff? Hoping someone can figure this out before I call for the 3rd time because we are stuck with the backlight on.

2) The Actual Temp drops 1 degree when you go to start the AC. Actual=74 & I Set=73, then Actual drops to 73 immediately & doesn't click on. You then have to go to 72 to hear the click on & reset to 73. So now I click down 2 degrees to 72 to hear the click & bump up 1 degree back to 73.

Anyone have this problem?

I've seen many badly designed thermostats that over and undershoot the
set temp. I've always tried to stick to brand name units, like
Honeywell. It could be a software issue or even warmth radiating from
the LED used as a backlight.

OT, a little: I once had a Buick Park Avenue that had a thermostat for
the heat and AC. When the car was left out in the Chicago cold, it
would overshoot the set temp by something like 20 degrees. Of course
the dealer thought I was a nut case. But I did measure it with
instruments. I found that the senor was sucking in air from a trough on
the dash. And because it was a big hunk of steal and plastic, it stayed
cold for a long time. Eventually, it would warm up and then would work
properly. But this would take a about a half hour or so. I moved the
sensor to a better place ... problem solved.