For my 86.5, the part number for for outside temperature sensor is
The sensor comes housed in a metal cylinder, which goes in-line with the alternator cooling duct attached to the front side of the flat plastic wheel-well panel that mounts in front of the left front wheel. The sensor has about a foot of cable, which has two conductors (wires) and a two-pin round rubber connector at the end. On my 86.5, I recall that the mating wiring harness was routed through an access hole in the inner fender near where the ABS unit mounts. The connectors and loose cable are pinched to an inner fender brace by a metal tab, I guess to provide strain relief or to prevent the cables from rubbing against metal.
The sensor is a variable resistor and is connected in series with two other variable resistors: the INSIDE temperature sensor, and the temperature control setting in the AC control unit. So problems with any one of these can cause the same symptoms. The variable flap control unit monitors this circuit and, in conjunction with other inputs, determines how much heated air to mix with the cool air. If you don't mind taking things apart and if you have a Multi meter, a schematic, and a little aptitude, you can diagnose problems in this circuit.
In my case, the connector pins (on the outside temp sensor) were corroded so much that I had to cut off both connectors and solder new ones on. After that, the "all heat all the time" symptom abated.