Thermostat temp difference between heating/cooling

Factual Questions
1

We have two of those standard round Honewell mechanical thermostats for heating and cooling (CT87), in two different areas of the house (two different heating and A/C systems).

When the heat is on, the temperature shown on the built-in thermometer is pretty close (about 2 degrees) to the thermostat setting.

But when the A/C is on, the temperature on the thermometer is 6 degrees or so lower than the thermostat setting. To get a room temp of 74 degrees, we set the thermostat to 80.

That’s true of both thermostats.

Any idea why and what we can do about it?

2

Mechanical thermostats are very inaccurate. I don’t know why their is a difference
between the heat accuracy and the AC accuracy… but
I would suggest just switching to digital thermostats. Cost is not a lot.
About $40.00 per thermostat for a basic non-programmable one!