Low Pressure Dryer Switch ( Near or next to the Dryer front of Radiator Area
Link to this Info :
THE 928 HVAC SYSTEM
starting with the 1980 year type , and yes there were two versions , version one= Non Climate Control( can be recognized by NO temp sensor vent in center console(upper section) . Version two= Climate control (has the temp sensor )one inside as mentioned and one positioned outside in the left front guard area. Also for the 1980 to 1989 is the large and highly respected N/D A/C compressor , and from 1980 to 1986 a much larger A/C condenser electric fan , the non climate control version was deleted around the time the 4.5 928 was discontinued .
As is often the case with a 928, the most common problem with the electric cooling fan seems to be bad connections on the fuse or a bad relay. The fan motor, coolant temperature switch, refrigerant temperature switch, and wire harness can all fail, but these failures are much less common than fuse and relay problems.
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Another problem with the electric cooling fan is that the refrigerant temperature switch seems to be ineffective. It would be better if the electric fan ran any time that the A/C compressor was operating. One way to accomplish this would be to install a heavy-duty in-line relay, triggered by the A/C compressor signal, to operate both the compressor clutch and the cooling fan. A diode should be used at the fan, to prevent triggering the compressor when the temperature switches operate the fan.
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The electric cooling fan may not run as often as you expect. On cars up thru ‘86, the fan does not automatically run when you turn the A/C on. It only runs when the coolant is very hot or when the Refrigerant temperature switch is triggered.
To check the electric cooling fan, turn the ignition switch on, pull the connector from the refrigerant temperature switch (located on the stem sticking up from the receiver/dryer between the radiator and the bumper), and jumper between the contacts in the wire harness. The fan should run.
If the fan does not run, replace the connector, and pull the cooling fan relay (not the blower relay). Jumper between terminal 30 and 87 in the relay socket - the fan should run. If not, check for 12 vdc at the fan motor connector. If there is 12 vdc at the fan connector and the ground is good, but the motor does not run, the fan motor is probably bad.
Note from Aluminum :
I am Not sure where the location of the evaporator temperature sensor is but under the dash I think on the Drivers side