The building I am in has about 75 Mears Model M401 thermostats and neighbors all report similar problems to mine: we seem to have no actual temperature control. I spent yesterday and today with it and a room thermometer to find out the following:
Set thermostat to about 66, yields room temp of 63. Turn it the most minuscule amount higher (about the thickness of a piece of paper) yields room temp of 66 degrees. Turn it up again the most minuscule amount possible, the room temp becomes 75 degrees. No kidding, I am sick of either freezing or sweating all night and 2 nights ago couldn't even get back to sleep; suffice it to say I've had it. Pulling the cover off reveals on the inside of it text below a picture of what almost looks like a tiny "push pin", and "CAUTION: any knob setting below 50 degrees may result in freezing."
Looking UP at the bottom of the device and it almost appears that the knob is like a "ramp" and applies varying pressure to a metal plate based on it's position. Well, there's a tiny screw which looks like the picture and I'm guessing when these thermostats were installed, none were calabrated and whoever tightened the "push pin" screw turned it until s/he was bored or some similar event. IF I TURN THE SCREW, which way should I turn it to get the "one cover plate inch = ten degrees" setting the cover plate indicates? Is there someplace online I can find this answer if there's no answer here? 24 units worth of people are waiting to hear back (I'm a real estate Broker.) Thanks for your time and assistance in advance.

I can find no useful information on these thermostats, other than they are commonly used in line-voltage applications. Unless you can find someone who has actually encountered one of these, you may have to rely on a trial-and-error approach regarding calibration, or find suitable replacements for them. Good luck.

I'm not trying to sale or scam any one and charging a fee for information that is not even correct , Well I just would not pay some one that I can only hope is right answer. I do know you were given the wrong Information . I have been a HVAC Tech for 22 year's , a universal tech at that which only means only means something if you're a tech. So having said that free of charge the answer information, is as follows. Your air handler / furnace is a 90% efficient unit . The exhaust out let or pipe if you will , is PVC piping is ran horizontal depending on location of Installation and if it is Installed so the pipe is not sloping to the out side or has a dip in the middle, the condensation/ moister will plug or shut off air flow and cause the OCM/operational - control -module or computer board to not close any switch's /or let it run . That is so if the pipe is blocked the exhaust won't back up back in to your house. On all newer unit's are equipped with Diagnostic computer board's .The information you need to access the diagnostic system and the code's that indicates the problem is found ether on the inside of the fan access panel , where you should also find the OCM/diagnostic computer board, or at your HVAC dealer or part's store. My bet , the exhaust is full of water!
Good Luck

I'm not trying to sale or scam any one and charging a fee for information that is not even correct , Well I just would not pay some one that I can only hope is right answer. I do know you were given the wrong Information . I have been a HVAC Tech for 22 year's , a universal tech at that which only means only means something if you're a tech. So having said that free of charge the answer information, is as follows. Your air handler / furnace is a 90% efficient unit . The exhaust out let or pipe if you will , is PVC piping is ran horizontal depending on location of Installation and if it is Installed so the pipe is not sloping to the out side or has a dip in the middle, the condensation/ moister will plug or shut off air flow and cause the OCM/operational - control -module or computer board to not close any switch's /or let it run . That is so if the pipe is blocked the exhaust won't back up back in to your house. On all newer unit's are equipped with Diagnostic computer board's .The information you need to access the diagnostic system and the code's that indicates the problem is found ether on the inside of the fan access panel , where you should also find the OCM/diagnostic computer board, or at your HVAC dealer or part's store. My bet , the exhaust is full of water!
Good Luck

How do you know what they have, they only mentioned a thermostat? This is in a 24 unit complex, most likely zone controlled. BTW, the post is 6 years old!!

Hi all!Amazed I am still getting responses to this; thanks for your time!I actually bought a small space heater and used that and eventually moved. The thermostat was connected to electric baseboard heat.Happy 2016!