I got another thermostat. it matches the older dial unit. says 70 now. so im voting for 2 out of 3 being right.

Is the thermostat on an outside wall? What's the insulation status? Perhaps there's warm air filtering through the hole for the wiring? Place one of your thermometers atop the thermostat to check what it reads there. If it matches the thermometer atop the picture frame, then presume the thermostat has gone wonky. Also, some digital thermostats have a adjustable temperature offset. Check the programming for whether yours does and whether it's set to read 6°F higher than the actual room temp.

Most digital thermostats have a "temperature offset" setting to match your old mercury bulb.

What you all are calling offset might be differential between wet bulb and dry bulb.

No, nothing so sophisticated, it's just an adjustment of the display reading if the thermostat isn't reading the correct temperature..

Accuracy of a thermostat isn't nearly as important as repeatability. If the thermostat says "74F" and that's comfortable for the occupants, it doesn't matter all that much if the true, calibrated, temperature is 70F or 72F or 76F. What matters is that the thermostat consistently registers 74F at those same conditions and that the system is capable of controlling to achieve it as a setpoint temperature.

Chas Ross gets a sticker and I have a confession. While striving to maintain a reputation for honesty and quality work I deceived countless home and office occupants in the name of selling them "satisfaction".

It began during the big energy crunch when news people,greenies,the gubment and other experts recommended everyone set their t-stat to 78*F. Complaints rolled in from people saying they were sweating while their friends were comfortable so something must be wrong with the equipment. I simply tweaked the stat so it cooled room to 74* when set to 78* and they were happy. Don't underestimate how much of a situation is in the head. Before you jump my case for not doing my part for energy conservation and environment let me say the experts deceive when they claim it's cheaper keeping room at same temperature rather than cooling it down after being away for hours.

New thermostat is working as expected. the ac is actually cycling on/off during day. which it was not doing yestersay. or last week. or 2 months ago.. it did not go above 72 all day. did not hit 73. or 74. or 75. in august. crazy

we set it to 72. the display will go 74. then 76. all day. and the ac will never shut off. it normally runs 100% from 10am to 7 pm. it never shuts off. now it does.

I've heard of others having the same experience. The only logical conclusion is that it is caused by hanging with houzzers. LOL

My house has poor insulation and crappy windows. it is 66f outside at 7am and it is 72 inside. lots of junk in house. its a big heat mass that takes a long time to adjust.

66f at 7am !!!!! You should change your screen name to Lucky Ducky and thank the big quackers in heaven instead of complaining to poor ol klem who saw 83f at 7am this morning and watching mercury rise to an expected 103f this afternoon. If that isn't enough to roast your nuts,the heat index is usually 5-6 degrees higher. ); Ray is just down the road a spell so y'all take that into consideration before picking on him,the heat's making him mean.

Of course my thermostat wont make hvac perform better. it did get to 73 a few days ago. but then it dropped back to 71. has been cooler lately. actually got some rain.