Topic: Making blower work with missing a/c compressor

[toqwik]

I'm sure it's been covered before, but mine is missing the a/c compressor, and they hacked into the blower harness to make blower run at 1 speed operated by a toggle.  I remember someone saying the system is grounded thru the a/c compressor.  What do I need to do to make this function correctly?

[Lt Shaffer]

I'd like to know also. I'm in the same boat.

[ta78w72]

Is your heater/AC slider still intact?

The way this works.....the A/C slider switch provides the current to the low setting of the fan switch as well as the brown wire to the resistor.  So, if that slider switch is still wired, it's an easy job for the rest but you need the wiring for the resistor and high blower relay.

If you don't have the switch and wiring, you'll need a service manual to figure out the wiring to build your own harnesses.  You'll need switched power to the low setting of the fan switch as well as to the brown wire of the resistor.  Then it's just connecting the wires correctly from the fan switch to the high blower relay and the resistor and blower motor.  You'll need the red wire from the alternator to feed the blower motor on the high setting.  The high setting bypasses the resistor and shuttles current directly from the alternator.

As far as the ground, usually it's on the AC bracket but you can ground the circuit it somewhere else.

[Mwieczorek]

Hey guys,

I wrestled with this problem earlier this fall.  I have a circuit diagram that I sketched up, I'll try to draw up a neater version in the next day or two and post it here.  I have voltage at the blower motor terminal, but I haven't been able to test it because it turns out my blower motor is shot.  Grrr...  My rear end it blown apart 'cause I'm instaling subframe connectors and traction bars.  Once that's done I'll get back on the blower issue.

Matt

[Bandit one]

Really?? You have to have the ac compressor in and operating to make the blower fan work? I was just about to attempt to fix mine. All i thought i would have to do is replace my blower motor and i would be on my way! I have a 78 SE and the ac compressor was removed by the previous owner and always assumed the blower was at fault. I have owned this car for 18 years and was just now going to fix this problem....procrastanator....and would like any info as to where i would start. I thought it would be a fairly easy job, but now i am starting to wonder. lol

[Mwieczorek]

No, you don't need the A/C compressor to run the blower, that's just how the factory has it wired to wok.  You have to do some wiring work to run it without the A/C compressor.  It's not hard at all.  The biggest things you'll have to do are to run a new power wire from the alternator to the blower motor, and to run a new ground for the blower.  I have a ground strap that runs from my firewall behind the engine down to the passenger side head.  I simply ran a wire from the ground terminal on the blower to that grounding strap on the firewall.  I ran a 12 ga. red wire from the alternator back the driver's side and around behind the engine over to the blower motor.  It's not the shortest route, but it allowed me to keep the power wire inside my wire loom so it looks neat.  Other than that, I had to do some minor re-routing of wires on the blower speed resistor pack and the high blower relay.  I'll run out ot the garage when I get home tonight and get the diagram.  Then I can scan it and post it for you.  Just make sure you test for voltage at the spots where you need voltage and ground at the spots where you should have ground and you'll be fine.

Matt

[ta78w72]

When the A/C is removed, the bracket for the compressor is most likely also removed.  This is where the blower motor circuit is grounded.  That's why the blower motor stops working....loss of ground, not loss of the A/C compressor.  If they also cut wires, you'll have to rewire the circuit.  It isn't hard, but does take some thought.  Here's the circuit wiring diagram from the service manual.

[attachment removed by admin over 60 days old]

[jcurrieta]

i am in the same boat also but i have a blower motor non ac harness im debating if i sould use.....i also swaped the whole houseing to non ac also.......should it plug right into my under dash wireing harness??

[ta78w72]

i am in the same boat also but i have a blower motor non ac harness im debating if i sould use.....i also swaped the whole houseing to non ac also.......should it plug right into my under dash wireing harness??

My guess is it would.  But it's only a guess based on the desire of gm to produce as few variations as possible.  That's why add a rear window defroster is so easy.  And the power trunk release.  But you'll have to look at the wire combinations and the connectors to see if they fit.  If the connectors fit, you can rearrange the wires to work.

[Mwieczorek]

Ok gang, here's my simple A/C elimination wiring diagram.  You'll have to forgive my sloppy drawing...



I had to replace everything from the firewall out, so I just wired it neatly and mounted everything to my A/C delete blower box.  Just so you know what everything does to help with troubleshooting: when you set the blower to low, the brown wire from the firewall provides voltage to the resistor pack, it passes through all 3 resistors, thus lowering the voltage and providing low speed, the white and black wire passes through only 2, providing less voltage drop and a higher blower speed, the blue wire passes through only one resistor, providing even more speed, but less than the full system voltage.  Only one of those 3 wires should be hot at any time.  The voltage from the resistor pack runs to the normally closed terminal of the blower relay, where it passes through and onto the blower to provide power.  When placed in "high", the orange (or gray and black, depending on your car) becomes hot and kicks over the blower relay to the normally open side, killing the connection to the resistor pack input and shunting full system voltage straight from the alternator to the blower.  The red wire from the alternator should be hot whenever the car is running.

I hope this helps to de-mystify this process for you guys.  Its not a hard system to wire, you just have to pay attention to the details.

Matt

[ta78w72]

Is the relay wired correctly in your diagram?

I think it goes...from top to bottom

Ground
Orange from switch (high setting)
Hot to blower motor
Red from alternator
Output from resistor

Did you test this circuit?  I could be reading the diagram incorrectly.  Otherwise, it looks like it does the job.

[Mwieczorek]

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

[Joker (§ir£Ğragon)]

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?

[Joker (§ir£Ğragon)]

Now that I go back to update my original post with the bad diagram I can't find it.   

Never mind. I found it. LMAO

[Mwieczorek]

Larry,

Yep, your diagram jives with mine, and looks nicer to boot!

This question comes up pretty often, so we really ought to get one of these diagrams, and a decent explanation of how the system works, into an FAQ here on 78ta or over in the tips&tricks section at TAC or something.  That way we can just refer people to it in the future.

Matt