Fan will not operate at HI speed

[leddzepp]

I have a 68 factory AC system, and cannot get the fan to operate on HI speed. I have swapped in both a control panel switch and a relay (located on the side below the glove box) and the results stay the same: the fan will operate at LO speed (sounds tired and slow), medium speed seems OK (not really robust), and HI speed, it craps out and runs real slow, or almost not at all. Is the fan just "wore out", or am I missing something else?

[70shortfleet]

There is a coil that is inside the evaporator/heater core box down by the diverter, it could be that?

[jjzepplin]

My problem was the ground to the fan motor. I ended up running a ground straight to the battery and my fan has never worked so good.

[Wrenchbender Ret]

There is a fuse in a inline holder comeing off the junction block that goes to a relay. The fuse is blown or the relay is defective.

[leddzepp]

There are no inline fuses present. I believe those are located on the headlight harness most of the time, and would have no bearing on the fan motor? The only relay is the one in the cab on the side of the box.

[70LonghornCST]

Scott, I'm inferring that it has a fan clutch. Is it new?

[davepl]

The HIGH setting on AC trucks is provided by a direct line from the fusebox (IGN UNFUSED maybe) and goes to a relay on the right hand side of the heater box by the passenger's feet.

When the HIGH setting is selected it provides a trigger to the relay when then feeds the maximum 12V current directly, bypassing the resistors and everything else. I've never seen an inline fuse in my original harness nor my new one.

I would guess, then, that one or more of the following is true:

a) The orange wire is missing, not connected, or there's an interruption somewhere
b) The relay is bad
c) The switch is bad

Easiest thing to check is whether the output of the switch that goes to the relay is going hot when you set the switch to HIGH.

[leddzepp]

Thanks for the replies everyone! After wiring the fan motor directly to the battery it spun as it should,so I went back and looked everything over once again. Then I compared it to my 72 setup, I noticed a small black ground wire present on the relay...which was not present on the 68. I reached up and found the wire dangling on top, connected it, and all is well! I am guessing a PO replaced the relay a long time ago (it looks new, but is USA made so it must be old) and neglected to connect that ground wire. One step closer to getting the factory AC going again

[jjzepplin]

I knew it was the ground! LOL!

[68Gold/white]

Most of the GM stuff uses a small bent piece of metal that a wire, w/ a push on connector attaches to. It's a poor connection at best. Post 3 ran a ground wire direct from battery. that is best, but not entirely needed.
Sand the paint off one of the areas where one of the screws are, that attaches the blower motor to the evap., or heater case. Connect an extra wire there, and on engine, that will help also.
This mod. can help ANY GM vehicle...

[jjzepplin]

Boo! Now mine has taken a crap at high speed. Was fine til I said it was working great!