New Carrier AC runs past setpoint when I shut thermostat backlight off

We have a new Carrier furnace/AC & Touch & Go thermostat.
1) The AC keeps running past the setpoint but only shows the setpoint as Ac tual temp. Sets Actuals 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, th at makes the AC run on. So I turned the U2 backlight back to ON & now it st ops at set temp. Why is the backlight controlling the AC shutoff? Hoping so meone can figure this out before I call for the 3rd time because we are stu ck with the backlight on.
2) The Actual Temp drops 1 degree when you go to start the AC. Actualt & I Sets, then Actual drops to 73 immediately & doesn't click on. You t hen have to go to 72 to hear the click on & reset to 73. So now I click dow n 2 degrees to 72 to hear the click & bump up 1 degree back to 73.
Anyone have this problem?
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On 8/15/2017 11:56 AM, JR wrote:

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.
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On Tuesday, August 15, 2017 at 11:56:20 AM UTC-4, JR wrote:

Actual temp. Sets Actuals but real temp is 71. 1st repairman said i t was normal to run 3 hours for 1 degree
Sure, if it's one of the hottest days ever in the area, 100 and you're trying to maintain 70, I can see that. If it's 80 out and you're trying to maintain 75, it should't take 3 hours to go from 76 to 75, unless the unit is way undersized.
& be 2 degrees colder than setpoint
Time to get a new tech. I've never had any thermostat go 2 deg lower than set, nor would many people put up with that.
& 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, th at makes the AC run on. So I turned the U2 backlight back to ON & now it st ops at set temp. Why is the backlight controlling the AC shutoff? Hoping so meone can figure this out before I call for the 3rd time because we are stu ck with the backlight on.

4 & I Sets, 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 d own 2 degrees to 72 to hear the click & bump up 1 degree back to 73.

IDK what's wrong, but it doesn't sound right. Higher end thermostats have various programming options, some including how far over or under the temp it will go. Do you have the full manual? Call Carrier help?
I hope this HVAC just has the old conventional interface for a thermostat. It looks to me like some of the high end type sources are now forcing you into their thermostats which may have a different interface so you can't easily switch.
Like Art said, Honeywell makes excellent thermostats. I have experience with several of their VisionPro and they are easy to set up, easy to program, good features, etc. If I was buying a new one today, I'd probably get an internet connected one so that is away on a trip you can check to make sure it's working, or if you can't remember if you set the temp back you can do it remotely. And you can fire it back up on your way home, so it's at the proper temp for you when you get there. Mine has a vacation mode that kind of does that, you can set a vacation hold of X days.
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On Wed, 16 Aug 2017 07:29:47 -0700 (PDT), trader_4

Things get fancier every year. My new Lennox will go up to 3 degrees below the set point in order to lower the humidity. (That feature is can be disabled and the number of degrees is a user setting).
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On 8/16/2017 12:56 PM, Pat wrote:

Humidity control is important to comfort and not easy to control economically. Some years ago my father was the maintenance engineer in a printing plant. humidity control was more important that temperature control. The plant was air conditioned for that reason, not for employee comfort. On cool but rather humid days the AC did not run enough to removed the humidity so they cranked up at least one of the heating boilers to warm it up enough to run the AC.
I don't know the capacity of it, but I do remember walking into the plenum with room to spare.
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On Wednesday, August 16, 2017 at 12:57:01 PM UTC-4, Pat wrote:

That's a good point, who knows what features and settings it has. I remember that being discussed here before, that if it has humidity control feature, it can go lower than the set point if the humidity is still too high.
But if it really takes 3 hours to lower the temp by 1 deg on a day that's not extreme, seems something is wrong. Of course we don't have all the info, like what the starting temp is, the desired temp, how hot outside, etc. That would help. I think we'd all agree that if it's 80 out, 77 inside, set to 74 and it takes 3 hours to go down 1 deg, something is wrong.
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