1990 tempo

Assume you mean, temp wise.. not the blower speed.

Would be the 'blend' door in heater housing is broken or stuck.

There are two doors, diverter (DEF-floor-vent, etc) and blend which sets the temp get under dash and see which is not working tho door may be loose inside heater housing.

You need find someone who is used to actually working on cars, not just changing oil on them.

Quik temp fix:

uncouple heater hoses at firewall into cabin and connect together with short piece of tubing (or barb connecter) and clamps.

Fan stuck on? Pull the power connector off the fan motor, make sure there isn't a latch on the connector you have to push/pull/trip first. Pulling the heater fuse might do it - but they usually put multiple systems on one fuse, and the other things that get turned off might be important to you.

Heat stuck on? The quick fix would be to manually close the heater valve. Mechanical heater valves are simple, loosen the screw securing the cable sheath, slip the actuating wire off the valve crank arm, and move the crank arm to the closed position.

Vacuum actuated heater valve - pull and plug the vacuum hose, if the valve doesn't close by itself under spring pressure you may have to pull the little linkage shut. And the spring failure in the actuator would explain why the heat stayed on even with the control off.

'Backyard Mechanic' implies that there is no heater valve on the coolant line of that model, and they depend on closing the air damper. That would be stupid design, but I wouldn't put it past them... In that case he's right, you'll have to rig a bypass or place a manual heater valve in line to turn of the hot coolant input to the heater core.

-->--

No water valve on a Tempo.

Vacuum actuated water valves default to full heat with no vacuum. They close when vacuum is applied.

I don't think that there has been an American car made since the late 70s that didn't use this design. I recall that, possibly, Chrysler products used them much later.

Everyone who's seen a water valve on a Ford in last twenty years raise hands... Bueller? Anyone?

Everyone who's noted that most common failure mode on old cars seemed to be water valve, raise hands..

No... Merkur's dont count

Meant heater failure mode, of course.