A/C blower motor with a mind of it's own

[Earl Filter]

I'm getting around to getting some A/C back in this thing (it's hot in Houston!), and here's what I have:

The blower motor was disconnected at the motor itself when I got the truck. After fiddling with it, I found that when plugged in, the motor will run on low with the truck turned off (and was probably killing the battery, and is why it was unplugged). With the truck on, it blows on low, no matter where the fan selector switch is, except if I move the A/C control to MAX, the fan blows on high, no matter where the fan selector is. If moved to normal A/C, defrost, vent or anything else, the fan blows on low. I bought a blower motor relay for grins, but no change in activity. Is the A/C control head the problem? What do I check next? I bought a new fan switch, but I haven't installed it yet. I figure it will be an exercise in futility, as I don't believe that is where the problem is.

Secondly, when the fan does blow, I get most of the air out of the heater vents, and some from the A/C vents no matter where the contol is set.

How can I go about troubleshooting these issues? Thanks in advance!

[NeCrOmAnCeR]

With the A/C control set ot max the fan will only blow on high, so that is normal. Check the blower motor resistor for the problems with only low speed in any other position. But be sure to check the switch as well. Not having high in the normal positions but having it during a max cool setting points to the blower switch.

[Earl Filter]

OK, I'll install the new switch and see what happens. I still can't figure out the fan coming on with the truck turned off and the A/C selector in the Off position.

[NeCrOmAnCeR]

The blowers on our trucks always run with the ignition turned on, even witht eh selector turned off. So check to see if a previous owner made some creative wiring decisions with the power wire running to the control unit.

[Earl Filter]

Originally Posted by NeCrOmAnCeR

The blowers on our trucks always run with the ignition turned on, even witht eh selector turned off. So check to see if a previous owner made some creative wiring decisions with the power wire running to the control unit.

I guess I didn't describe that part of the problem very well...imagine if you turned your truck off and took out the key. I know it should be completely off then, but yet it runs on low speed. That's why the motor was unplugged when I got the truck, but I don't know where it's getting power from for that to happen.

[NeCrOmAnCeR]

....

Originally Posted by NeCrOmAnCeR

So check to see if a previous owner made some creative wiring decisions with the power wire running to the control unit.

[Earl Filter]

Nope...it may be a wiring problem, but it's a factory wiring problem if so. Everything from under the dash to the firewall is bone stock.

[NeCrOmAnCeR]

Are any extra loads plugged into the fuse box? Like a stereo or something which may be "seeking a ground" through the blower motor when the ignition is turned off?

[Earl Filter]

Nope, not a thing. It's all factory stuff. No added circuits for anything.

[mhicks]

What year is it?

[Earl Filter]

Originally Posted by mhicks

What year is it?

1977 - see signature

[mhicks]

Mine is a '73 and when all is turned off the fan runs on low and that is normal when the key is on.
With my AC control in the AC position and the temp control all the way to the cold position the fan runs full blast. In order to have an adjustment using the fan switch the temperature adjustment needs to be about a 1/2 inch to the right of full cold or the fan speed switch will not do anything.
I can put my AC selection switch in any other position but off and AC and my fan speed control switch works. I guess all the way to the left with it in the AC position is MAX yet it doesn't blow any harder than with the fan speed switch on High and the temp control switch a little to the right of full cold.

[Captkaos]

The heater fan coming on when the truck is on is a feature of the "flow-through ventilation". It was designed that way.

[Earl Filter]

Originally Posted by Captkaos

The heater fan coming on when the truck is on is a feature of the "flow-through ventilation". It was designed that way.

10-4!

But I KNOW the fan shouldn't run with the truck completely turned off.

I attempted to install the new fan switch today to see if there was any change, but the switch I got was missing a connection. The factory switch has a 4-prong plug that looks like this:

- -
-
-

and it also has a single orange wire that plugs in below that. The switch I got had the 4-prong, but no single plug below it. SO, I cleaned up the terminals on the old one, and pulled the a/c head, and cleaned the terminals on that, too. I then installed a tach , and just fiddled with a few underdash plugs, and cleaned a few connections.

Now, it seems to be working correctly, but I'm afraid to leave the fan plugged in until I can check it a few more times to make sure the fan isn't running on low while the truck is parked.

As for the second part of my question, where to I begin to get the flow coming out of the dash only? If I had to, I wouldn't mind getting it where it would flow out of the dash vents ONLY. I don't really need defrost, and the heater vents are rarely needed as well. I just need some full-blast A/C out of the dash! It's hotter than Hades, and will be until, oh, about OCTOBER!

[NeCrOmAnCeR]

Going back to the blower problem, (sorry) when the blower runs after turning the truck off, will the wipers run also? If so it may be a problem with the ignition switch.

To get air flow out of the dash vents, check to see that the vacuume line is conected to the engine intake and is in good condition. Then check all the way to the control head to make sure that all the vacumme lines are in good shape. If it all checks out you can always wire the vent doors open. You should find three vacumme motors (dash-pots really) under the dash. One all the way against the passenger kick pannel (A/C recirculation) one behind the glove box (defrost I think) and one above the tranny hump (floor / dash) check to see if the floor/dash door moves when set to that position with the truck running, if not try to move it by hand and wire it into the correct place to give you cold air.

[Earl Filter]

Well I didn't check before, but the wipers do not run with ign switch off now. I don't think they did before, as I've had the dash bezel on and off a few times, and I know I've moved the switch with the truck off, but the battery still connected. I'm hoping that whatever I did today (maybe made a better connection somewhere?) has fixed it.

I'll take a look at those doors, and see if I'm getting vacuum all the way.

Thanks for continuing to try and help me get this thing going!

[mikesz]

It might be your ignition switch. The switch has a seperate circuit for HVAC. It might be on all the time. I would get a wiring diagram and start checking stuff out.

Mike

[Earl Filter]

I fixed the blower-running-on-low-all-the-time problem, but I don't know how. Something in the switch connection, the relay connection, or something else I took off and put back on. So far, it hasn't acted up again.