If you have the hang-on evaporator head, there should be two, and maybe three, wires from it.  One is the AC power that comes from a fused (20-25amp) hot source to power the whole system.  The second wire goes to the compressor clutch, and the third wire, if there, goes to ground. 

On mine the motor ground wire was attached to the mounting bracket at the rear of the evaporator and was grounded to the dash when the unit was bolted in.

If one of the wires has an in-line fuse, that is the hot wire.  If you attach the positive of your battery to this and attach the mounting bracket of the evaporator to the negative post of your battery, the fan should run if you turn on the left switch.

The other wire runs from the three speed switch to the thermostat and then to the clutch.

You can operate the Temp knob and check for 12V at the second wire if you have a meter or test light.  That will tell you if the thermostat contacts are making up.

If you can't identify the power wire (no fuse or other identifing colors) then we have to do some detective work or you can remove the facia so you can see the wires and switches.

So, do you have an ohm meter?  Post again if we need to do it the hard way.

BB

Last edited by Bullet Bob (9/08/2013 12:12 PM)

They probably did not want someone turning it on with no freon in it because that would ruin the compressor.  The old systems did not have a pressure switch to cut out the compressor if low pressure conditons existed.

If the two large wires are still on it, one has a female plug. That is the compressor.  The male plug goes to 12volt switched power.

Of course, if yours is like mine was, the ends were cut off 20+ years ago.