With the key on and the fan switch in high. Unplug the 4 wire connector from the fan relay on the top of the evaporator box in the engine compartment.
Check for voltage at the 12 gauge orange terminal. If good your getting 12V from the battery, if not your fuse or fuse holder is bad.
Check for voltage at the 18 gauge orange terminal. If your not getting 12V then you have a problem with your fan switch on the dash, or the wiring between thw switch and this connector. If you are getting 12V (at both orange wires) then the relay is probably bad.
The relay coil is picked up by 12V between the 18 gauge orange and 12 gauge black wires. This closes a contact between the 12 gauge orange and 12 gauge purple wires. 12 Volts (some amount of current really) flows from the battery, through the fuse, through the contact, to a terminal on the blower motor resistor, and on to the fan motor.
Plug everything back together and toggle the switch in and out of high. If you can't hear the relay clicking when you put the switch in high, it's dead.
The two prong connector on the other side of the evaporator is the low temperature cut off switch. It will open if the air temperature gets down to 29 degrees or so and cuts off power to the compressor clutch. It keeps the evaporator from freezing up. Doesn't have anything to do with the blower circuit.
1969 Indy Pace Car
350/300HP RPO Z11
My 69 L48 - 350/300HP Engine
[This message has been edited by Mark C (edited 06-29-2002).]