1978 F150 XLT Ranger Regular Cab/Short Bed 351M/C6 4x4

Truck has sat for quite some time. When I flip the blower control switch to run the defrost, A/C, etc. . . The fan doesn't operate at any speed. I can hear the vacuum under the dash when I switch from the dash vents to the floor, defrost, etc., but the fan still never blows.

Also, I haven't checked the freon, but the compressor doesn't run at any setting, either. I thought I'd mention that, just in case these two issues were related.

I've read the following article :: Heater Core Removal and Installation For 1973-1979 Ford F-Series Trucks .: Articles

But, I don't want to start there if the blower motor itself isn't the culprit. I'm thinking that a mouse couldn't chewed a wire or two while the truck sat for so long, but I've got no way to prove that without testing the blower.

I have thought of pulling the A/C-heat control unit from the dash and see if there's a way I can "tap" into a wire and send power to the motor, but I wanted to see if any of you guys here have ever had an issue similar to mine. By the way, I've checked all of the fuses and they're good.

Any ideas? Thanks!

 

Turn the key to RUN, and check for power on BOTH sides of the heater/AC fuse.

 

Thanks for your suggestion!

I just went out and verified with a test light . . .

Every fuse in the fuse box has power at each end.

 

Assuming power is making it from the fuse (which you've verified is good) up to the switch through the dash, the next thing to check is power out of the selector switch. You will have to remove the instrument panel bezel and pull the A/C and heater controls forward.

On the back of the directional lever is an electrical connector. The ORANGE wire is power into the switch; you should have power here anytime the key is in RUN so long as the fuse is good. The RED with BLACK stripe wire coming back out should have power anytime the lever is moved away from the OFF position. Check if you see otherwise.

 

Thanks again!

I will pull the unit sometime this week and go from there.

 

In addition to all that great info above .... when you say you are gonna pull it .... and seeing as how we males of the species like pictures (we look at the pics in the menue while the wife reads it, we look at maps while she reads a set of directions, women are made to catch the eye of men, it's just nature) .... I thought maybe this link might be of interest.

NORTH COUNTRY SPECIALTIES ®

 

Anthropologically speaking, that is a fairly accurate statement. However, women were the gatherers and are more visually apt to distinguish ripe fruit. Women also tend to converse more than men because they socialized when out foraging..... men were the hunters and tend to have a better sense of direction. Men today "hunt" when they shop.. women tend to sample/test everything.

Back to the thread....

 

This sounds a lot like what I had to go thru. Check that relay.

https://www.ford-trucks.com/forums/1...eshooting.html

 

Thanks soooo much for those pictures!! They're going to come in very handy if I do indeed have to tear into the system to replace the motor.



Thanks for your information as well! I'm really hoping our situations have something in common . . .

 

WHA-LAH!

Pulled the ac/heat control unit tonight . . . I found that I had power going into the unit, via the orange wire, but no power coming out. I then disconnected the vacuum lines and electrical connections and pulled the unit forward.

What I did then was run a "jumper" wire from the battery and plugged it into the port for the red/black wire . . . The fan then fired up and ran!

Problem is the switch. Wonder what that will cost?

Thanks for all of y'all's help!!!

 

Switch, blower motor
fits 73-78 F100-350 w/ integral A/C before s/n CA0,001
D3TZ-19986-A Motorcraft# YH-2

From s/n CA0,001
D5AZ-19986-A Motorcraft# YH-264

There are quite a few of these switches out there. If you want some sources, let me know which one you have and I'll post contact info for some of the dealers/parts suppliers that have them.

 

Thanks!!

If by s/n you mean last digits of the VIN, I have CD1875.

I went ahead and pulled the switch completely out. I don't see any part numbers embossed anywhere on the switch itself.

What's the lime green/white wire?

 

Yes, that's your truck's serial number. You have the second switch listed.
Question, you are talking about the blower switch, correct? The reason why I ask is the green/white wire doesn't have anything to do with the blower switch. That wire is part of the a/c mode switch. It goes from the mode switch to the evap temp control (mounted by the evaporator). The brown wire that comes out of the switch goes to the compressor.
Here's a not too clear picture of where the wire goes.

 

Lol, I didn't clarify which switch . . . The switch I'm referring to is the bottom vacuum/electrical switch in the unit. It has a cluster of vacuum lines going to the back of it, along with a triple-slotted female connector containing a orange, a red/black, and a lime green/white wire.

I have yet to find a replacement except for in an old LMC Truck magazine. They show two switches, each listed with two different part numbers. I can't find any part numbers embossed into this switch anywhere. I'm planning on giving them a call tonight and see if they can give me some additional info to know exactly which one I will need.

After some further testing, I've proven without any doubt, unless there's a relay that could be blamed, that it's this switch. After I removed it from the unit, I ran power into the correct port and had no power coming out of either of the other ports. I then ran a "jumper" wire from the truck's battery to the red/black wire port, and the fan started running. I then inserted the "jumper" into the lime green/white wire port and could hear the compressor clutch clicking on and off as I pushed the wire in and out.

Reason I was asking about the lime green/white wire is because I thought of "jerry-rigging" the electrical function of the switch with a couple of toggle switches while leaving the vacuum portion to the original switch itself. But then, this truck is completely unmolested, and I don't want to start molesting it now. I plan on finding the proper switch and replacing it.

 

Look up under the glove box. Should be a silver/grey metal relay with 3 wires going to it. Possibly screwed to the edge of the dash for ground. Betcha that's bad causing no electric at the switches.