This is the answer. The computer causes this failure. Simply pull the negative battery cable off for 10 minutes. Put it back and you have cold air again. This happens all the time on my 2000 Mercury Sable. It is a matter of rebooting the whole system. Not only does it blow hot air but really hot air. You could die in there on a hot day. Even with the fan off it comes rolling in like an oven. Someone should really raise Cain with Ford for allowing such a horrible error to go through. Ok I'm done.
The coolant temperature sending unit on a 97 Mercury Sable is in the engine compartment. It is located on the intake manifold.
i have found that with my 97 sable the low coolant light comes on when my oil is low. same as your car can run hot when your extremely low or out of oil
On a 1996 Mercury Sable : The thread on cap on the engine coolant reservoir is the pressure cap / radiator cap
On a 2003 Mercury Sable : The thread on cap on the engine coolant reservoir is the 16 PSI pressure cap / radiator cap
On a 2002 Mercury Sable : The thread on cap on your engine coolant reservoir is the 16 PSI pressure cap / radiator cap
R134a freon............
The coolant sensor is on top of the engine. It is between the ignition coil and the tfi module.
In a 2000 Mercury Sable : The thread on cap on the engine coolant reservoir is the pressure cap / radiator cap
The thread on cap on the engine coolant reservoir of a 2002 Mercury Sable is the pressure cap / radiator cap
On a 2002 Mercury Sable : The engine coolant reservoir is at the front of the engine compartment , on the passenger side of the engine compartment ( the engine coolant reservoir has a thread on cap on it , that is your pressure cap / radiator cap )
On a 2001 Mercury Sable : The thread on cap on the engine coolant reservoir ( located in your engine compartment , on the passenger side of the engine compartment ) is the pressure cap / radiator cap
The coolant level sensor is bad. It is integrated into the coolant bottle, so you need to replace the coolant bottle.