I don’t know how many times I have explained this to my wife: if you turn the thermostat down too low it wont work. Whenever we get home from work we turn on the air conditioner. If I get home first I set the thermostat to about 73 degrees and then the house is cool and comfortable for my wife when she gets home. However, if she gets home first she sets the thermostat down to about 40 degrees and then she wonders why the air conditioner isn’t working. I have one of those older, dial, thermostats. The HVAC system in the house is not the original HVAC system. However, the dial thermostat very well might be. It works great so I have never had cause to replace it. The only issue is that if you turn the thermostat down 50 degrees, it doesn’t know what to do so it just does nothing. This has never been a problem for me. After all, it is not like the house cools down any faster at 40 degrees than it does at 74. The house cools down just as fast if you set the thermostat to an actually comfortable setting. In fact, it cools down faster at a normal setting because the air conditioner actually kicks on. It doesn’t if you set it too low. At this point I don’t know what to do except maybe buy a wifi thermostat. I understand that those can be pre-programmed. Then the house could just be cooled already for us by the time we get home. No matter who gets home first.