Topic: Making blower work with missing a/c compressor

[ta78w72]

Why not use the schematic out of the service manual?

[Rebel 5150]

Why not use the schematic out of the service manual?

Not quite that easy when converting a A/C car to a non-A/C car.  You are basically creating stuff GM never intended.

[ta78w72]

You dare question an electrical engineer on his circuit diagram?  Blasphemy!  Just for that your hard disk will crash and your power will go out for the next week!   

Seriously, though, the wires hooked to the relay aren't in any particular order in my diagram, I just drew up the guts of a standard 2 input relay and put the wires where they needed to go.  I was doing this after hours at work, from a combination of the posted diagram and my memory.  My home scanner is down and I wanted to get something out for these guys today so I was in a bit of a hurry.  The terminals aren't in a line on the physical connector anyways, for that matter.  The actual connector (when viewed from the plug in side) looks like this:

      __
    |     |
      __
      __

Looking at the picture, the top horizontal connector is the output to the blower motor, and should be wired with a 12 gage wire (red if possible because it's hot), the left one of the 2 vertical connections is the orange (or gray and black) it is the hot wire that activates the relay.  The 2nd of the verticals is the relay activation ground.  The 2nd horizontal connector is the output from the resistor pack, it is the normally closed contact on the relay.  The bottom horizontal connector is the normally open contact, it is connected to the hot wire coming from the alternator.

I have probed the circuit in all states and everything works as advertised.  The blower in my car is junk and I haven't had a chance to remove the fender to replace it yet.  I know it's the blower because I hit it with +12 and ground straight off a DC power supply and it didn't spin at all.

Just to let you guys know, both the connector and relay are available from Advance Auto Parts online.  You're on your own for the resistor pack, though.

Matt

Hey Matt, with your input I updated the wiring diagram I had found. Apparently they didn't even include all of the fan speed positions nor even the relay (and I had totally forgotten it.)

Does this look right to you?

It's not correct.  Sorry guys.  The blower motor switch has one lead in and three leads out.  Not as shown.  The power for the low setting to the resistor is from the rotary switch which isn't shown in either diagram.  To correct the diagram, you need to split the power lead to the switch in two, with one line running as shown to the switch and the other line to take the place of the wht or brn lead from the switch to the resistor.

Mwieczorek's diagram is OK because his concentration is on the wire colors which are correct.

[Joker (§ir£Ğragon)]

Rotary switch? Do you mean the slider control? Or g) I'm remembering something else which may be what you are meaninis it supposed to be on low speed all the time for the ventalation/circulation as GM designed for awhile?

[Mwieczorek]

Yes, you are right that Larry's diagram has the power for the low setting coming from the wrong spot.  It was early and I still hadn't had my 2 cups of coffee when I reviewed it.  The power for the low setting actually comes from a the "mode" switch inside the heater control (you know, the one that says vent/heat/floor/defrost, etc).  BUT, all of that stuff is internal to the heater control, you can't see it from the engine bay, so as long as you still have the wires coming out from the cabin, you don't need to worry about where the power for low is actually coming from.  That's why I left that part off of my shematic.  If we were dealing with engineers who were curious about why the system works the way it does, then it would matter.  That's not the case, we're dealing with people who just want to make their blower work without drudging up all the junk to replace the A/C system. (Who wants A/C anyways?  It's heavy and restricts access to the passenger side spark plugs.)  If the HVAC wires are still hanging in your engine bay and you follow the diagram I provided, your system will work.  Simple as that.  If your wires are missing, then you need to get into the heater box and re-connect to the proper places on the box.  That's where the service manual comes in handy.

Matt

[Joker (§ir£Ğragon)]

That's an easy fix. Might as well have it close to right in case anyone needs that area as well. Thanks for the correction!

[dfred]

i did the opposite, put ac in my car, here's a circuit out of the 78 service manual

[Joker (§ir£Ğragon)]

There we go. Reloaded the modified version. lol

[egman40]

hello
ive been reading this topic and got to thinking
instead of rewiring without the compressor installed, since the bracket is where it grounds. coudnt i just use the ac harness and use the ground from it to the chasis?