I have a 2001 mercury sable DOHC and my heat isn’t working anymore. It was blowing on and off or a week, with barely warm air. I just ignored the problem. A couple days ago it wont even blow at all. Whenever I try to engage the heat, I hear a little clicking noise, even when I switch the settings to cold air. I’m thinking the blower motor is going bad or is bad.
Could be the multiposition switch or the motor itself. You might be able to unplug the wires to the motor without having to take apart too much of the dashboard, then see if there’s voltage to the motor.
Shanoia is correct on testing the blower motor.
In addition to that re barely warm air, most likely blend door is not operating correctly.
Less likely but possibly heater core is partially obstructed from deposits. With motor fully warmed up and heat on high, feel both of the heater hoses.