Your 1996 Mercury Villager minivan with the 3.0 L - SOHC V6 engine is designed to use The Ford Motorcraft RT 1170 thermostat ( 190 degrees F / 88 degrees C )
If you are asking about the engine thermostat, they are not adjustable. You buy them by the temperature setting.
Stant corporation produces 90% of all original equipment thermostats. Check with the parts house to obtain the proper temperature setting. Each cars thermostat tells the computer when the thermostat opens so in turn the computer will adjust fuel air mixture. This is very critical because if use put one in that opens sooner than required by the computer then the engine will run to rich of a fuel mixture.
On will turn the fan or blower on continuously and auto setting will kick off and on according to the temperature setting on the thermostat.
Each has a different temperature setting, so each needs its own thermostat.
A temperature setting on a thermostat
According to one of Fords websites : For a 1994 Mercury Villager , 3.0 liter V6 engine : ( the spark plugs are gapped at .032 inch )
It depends on the ambient temperature and the setting of the thermostat.
195 degrees F
Depending on your temperature setting, usually the best is about 70 degrees, it's best to set the thermostat, and leave it at a constant setting. Resetting your thermostat to higher temperatures requires the furnace work harder, and will usually increase your utility bill.
The temperature at which you are comfortable. If your question involves money-saving, then contact your local power company to determine the best setting.
Your contactor in the outdoor unit is stuck closed.
The answer depends on the thermostat setting as well as the kind of heating system that you have.