This is a 1980 F150 with factory air.

One day the blower motor just stopped. I have replaced motor, and resistor. I have 12v and ground at motor. But it will not run. If I put 12V from battery, it runs through ground at motor, about 2AMPS.
But I can measure 12v at motor connector.

I found a connector below radio, pulled it apart and no 12v to motor, so must feed fuse or go from fuse to motor.

My assumption, is the 12v feed does not have enough current to drive motor, since I can run motor from battery.

In the attached drawing, I think C606 is the connection at the motor. if so, there should not be anything between fuse and motor. Maybe clean fuse connectors?

But where is S 603? Is that the Function control in dash AC panel?

 

An "S" is a splice, "C" is a connector, and "G" is a ground - as explained on Page 3 of the EVTM here: HOW TO USE THIS MANUAL - ???Gary's Garagemahal. The location of many of those things is shown on Page 81 here: Heating, Ventilation, & Air Conditioning - ???Gary's Garagemahal. However, it doesn't show where S603 is, although your book says "For location of components see Page 62." Have you looked there?

Anyway, let's diagnose this. (Did the exact same thing a week ago tomorrow with Cashman on his 1980 F100 w/factory air.) Your diagram makes things somewhat confusing, but Page 83 of the EVTM on my site makes it much more simple. Power goes through the fuse box to C606, which is the connector to the A/C Heat Function Selector control above the ash tray. And there are two switches in one - one to control the compressor and one to control the motor, and they are controlled by the slide lever that goes horizontally. Then power goes to the fan motor on the Orange wire. Out of the fan motor power goes through the resistor pack to ground, and how many resistors it goes through is determined by the fan switch on the HVAC panel above the ash tray.

To troubleshoot the switches in the Function Selector control, pull the Orange wire off the motor and jumper directly to it from the battery. If the fan runs then there's something wrong with the switches in the Function Selector control, the fuse, or the intermediate wiring. And, that proves the resistor pack is functioning.

If jumpering power straight to the motor doesn't work then you have a problem in the ground side. Since you said you replaced the resistor pack, in this case you must have a problem with the wiring. But, let's take one thing at a time.

So, can you try that test and report back?

 

Thanks Gary, page 62 does not list the location of S 603.

I have powered the motor direct from battery and it runs.

Next, I will look at the function selector switch.

The odd thing is that even though the motor will not run, there IS 12V on orange wire at motor from Function Selector switch.

 

I think you were right at the start - having 12v showing on a DVM, and having 12v with enough current to run the motor are two different things.

 

Would a test light work in this case?
I would think it may light up but not bright?
Dave ----

 

Dave - It would depend on the test light. Some require so little current that they'll be full brilliance with anything. Some might not be fully bright, but you might have to look closely to tell.

Jmcgee - I should have said that the HVAC controls come out of the dash to the rear. I like to drop the ash tray assembly out and push the controls to the rear and then down. They won't come fully out even then as there are cables connected to them, but far enough out to get the electrical connectors off.

At that point you could use a jumper from the Brown/White to the Brown/Orange wire and bypass the switch. That would prove if the problem is the switch or is elsewhere.

 

There is 12V at the blower motor any time the function switch is in any position but off.

The circuit is completed to ground through the resistor pack(or bypassed for high)

Im going with, the fault is *after* the blower motor.

 

I would go there first, but I was able to jump directly from motor ground to ground at battery, and made no difference. Might still be a problem there, but the 12v isn't enough.

I did use a test light, and it lit but who knows what it takes to light that light.

 

Yeah, my father taught me this same concept, "Put a load on it" is what he would say.

You have this same kind of issue in the electronics world, too, just on a smaller scale.

 

Have you replaced the fuse?

I had a problem with my radio recently and was seeing 12v at the radio, but it was not even enough to drive the display.
Even though the fuse was "good", the radio came back to life after swapping it.

30A may be too much to make it through oxidized connectors.

 

Placing a ground on the motor ground and having it not run, and placing 12v on the positive terminal and having it runs proves the problem is on the high, or switch/fuse, side. As said, oxidized connectors can certainly do it, whether on the fuse or another connector. But Cashman's problem was a bad switch.

 

Thanks much Gary. I did jump Brown/White to Brown/Orange and motors runs. Put it back on switch, and no go.

Can anyone tell me a part number of this switch, or was the entire assembly sold as a unit?

I see 19B919 in book, but that brings up different parts on ebay.

 

E0TH 19B919 is the Identification Number, not the Part Number, for the vacuum control/switch unit for 1980 - 82 trucks, as shown here:








However, that is for naught as that is NOT the part #, and there is no reference in the catalog to that ID #, as there frequently is. So, I turned to the illustrations and found this:




So, now that we know you need 19B888 you can get the part # here. I think you need EOTZ 19B888-B:

 

.... or Motorcraft YH 361

http://www.ebay.com/itm/NOS1980-82-F...JXAaYO&vxp=mtr

 

Good call, Jim. I didn't know what YH-361 meant. Good find.

Oddly enough, I had that one on my work table and thought about throwing it away earlier today. It was left over from working on Cashman's truck two weeks ago tomorrow. Now we have this thread and the other one about the A/C compressor not coming on. So, in two week's time we could have had 3 of these bad? What are the odds?