my hvac has 3 settings
1. with the power off I can set the ambient temp for driver/passenger
2. press the auto button then set the temp I want driver/passenger/rear (a/c is auto on I believe as dehumidifier function regardless if you have it set to warm or cool)
3 press the power button and set the temp driver/passenger/rear/or defrost (with passenger disabled), a/c
when I cycle the key it remains wherever I left it last time I turned the key on, even hours or days later.
if yours does not stay where you left it last time you turned the key off then something isn't right, it doesn't change on it's own.
74deg is what it defaults to if you disconnect the battery for instance or unplug the control then plug it back in, so it sounds like yours is loosing the constant power connection when the key is turned off, I don't think a fuse would cause this but it couldn't hurt to check them and your grounds and maybe the plugs behind the control make sure they are all plugged in all the way
if you everything looks good you might have a bad control unit or it failed internally to keep power.
