so i had a new a/c switch installed because my high speed option wasnt working. so now my mechanic tells me i need a vacuum wiring diagram to hook it back up to high speed because the high speed option ran off of vacuum. can anyone please help me out? its hot as **** out here this time of year and im dying without the high speed. thanks in advance

 

Any way you can tell us what type of car this is for?

- Eric

 

71 cutlass 350 2bbl factory A/C car

 

Your High Fan speed has nothing to do with vacuum.

Your mechanic is therefore a criminal or an imbecile (possibly both).

Your problem also has nothing to do with your fan speed switch.

As has been explained here in numerous threads, the High speed is activated when the speed switch energizes a relay on the firewall or the evaporator box, which switches power to the fan to a direct line from the horn relay power lug.

Power goes from the battery, to the starter hot terminal, to the horn relay power lug, to the High Speed wire (orange if I recall), through an inline 30A fuse, to the High Speed relay, to the fan motor (purple).

Usually, the 30A fuse is blown, and a 25¢ fuse plus 60 seconds time will fix it.
If it's not that, then the relay may be bad.
If it's not that, then check connections. All of these wires are in the engine compartment, subject to 40 years of weather, and can get a bit corroded.

- Eric

 

ok so you're saying it might just be a fuse? if i pop y hood and go to the firewall, where exactly can i see this relay and fuse? appreciate your help

 

The exact location of the relay seems to vary with year, model, and options (such as rear window defog), but is generally on the right firewall or the evaporator box.
Someone with a '71 Cutlass may be able to be more specific.
The relay will have this supply wire, a big purple wire (to the fan motor), and two other wires (a small orange trigger wire from the switch "High" position, and another wire from the resistor block).

The wire goes from the power lug of the horn relay to this relay, with an inline fuse holder in the middle, usually in a hard-to-reach place (like just behind the distributor).

- Eric

 

popped my hood and just noticed the a/c box and another plastic unit next to that with a couple vacuum lines going into it???

 

u dont mean INSIDE of the evap box do you? or mounted outside of it?

 

ill check behind the distributor area as well ...

 

Black plastic cube-ish thing with two wires and two or three hoses is probably an aftermarket windshield washer pump.

Nope, right on a metal piece on the outside of the box, or on the firewall.
The relay can is metal, with rounded edges, and has to be attached to something grounded in order to work (so if it's hanging or screwed to the fiberglass evaporator box, there's your problem).

- Eric

 

so the relay can holds several relays? ill have to look at it more in depth tomorrow in the sun. man it would be really nice if i could just find a popped fuse and replace it. **** would make my day

 

No, just a single relay, not a few.

Here are a couple of pictures:





The relay in this case is perched on top of the evaporator box, and its wiring has been horrifyingly butchered.

If you look closely at the first photo, you can see one of those aftermarket washer pumps attached to the firewall just above the distributor.

- Eric

 

yeah definitely not mounted there on my car. So at least i have an idea. now ur saying there will be a fuse next to it or to change out the relay itself? appreciate ur input and the pictures i really appreciate it!

 

nevermind, went back and read what you wrote. i should find the fuse right near the relay.

 

Your junction block is on the firewall behind the disty. There should be a thick wire coming from it, going through an inline 30A fuse holder, to the high speed relay above brake booster.

 

Rob, that's not his car - It's just a shot of a '73 Delta I had lying around, that I used to show him the shape of the relay. That's why it looks different.

- Eric

 

Start with the purple wire connected to the fan and work backwards along the firewall. High speed relay on my '69 was by the brake booster.

 

Now that explains it.... I confuse easily in the morning.

The factory high speed relay should be on the firewall right above the brake booster. (FUSHIA ARROW)
Fuse holder (AQUA ARROW) comes off the junction block (YELLOW ARROW).
Here is a picture of my 72. I think 71 is similar.

 

Thanks, Rob, that's better information for him.

- Eric

 

wow dude identical! thanks a lot. ive been looking under my hood now for 20 minutes lookin for this thing. ill let u know what comes up. thanks again MDchanic and rob71!

 

well i was wrong its not the same


i have the relay right above the booster but i dont have that junction box with fuse. i saw a couple vacuum hoses going into the firewall (looks like it leads behind the dash) If i wanted to check the relay what do i have t do to get it out just pop off the top?

 

OK so i found on the driver side fender and another relay and it looks like thats where the junction box is because i remember MDchanic mentioned something about wired up the horn and i found what looks to be a connecting point of some sort. i unpugged it and it looks like a small cylindrical fuse is inside but i dont know for sure if thats a fuse or a connecting point for the female side of the plug. i dont wanna take it out until i know for sure what it is. i feel like im getting closer

 

Are there any wires plugged into it?

 

the junction point i found looks exactly like the one jon71 pointed out

 

You mean Rob72?

There should be two plugs into the bottom of the relay:
One with three wires: Thick Purple, Thick Orange (I think), and Thin Black/Orange (I think).
One with one wire: Thin Orange/Black.

If you pull off the single plug and touch a hot wire to it, the relay should click, and the fan should go on (if all else is working).

I would follow the thick Orange wire from the triple plug on the relay back to its origin at the horn relay terminal - you should find a fuse in there somewhere.

Next, use a test light or a volt meter to check that thick orange wire - it should show 12V all the time.

Next, connect a hot wire to the thick purple wire - the fan motor should run on High.

Next, put your test light on the thin wire in the single plug (Orange/Black?) - It should be hot at the High setting, and off in all the other speeds.

Next, put your test light on the thin wire (Black/Orange?) in the triple plug. It should be hot on the lower three speeds, but off on High.

After all that, you should have a good idea of where the problem is.

- Eric

 

eric it WAS the damn fuse! the same plug i was talking about. i just said F it and took some needle nose and the small fuse came right out. sure enough it was all fried inside so i went up the street and for $4.50 i bought an assortment set, came home, popped it in, fired her up and she blows perfect now. Thank you so much for your advice and guidance. I'd buy u guys a beer if I could! haha

 

You're quite welcome.

I think I'll just pour myself a beer anyway, and you can owe me for it .

And remember - don't trust your mechanic!

- Eric

 

yeah ill keep that in mind. ive only tried him once anyway but at least he installed my evap properly and got it blowing cold. thanks again! cheers!

 

Great - glad you got it fixed - for cheap!
That should be a 30A fuse in there.
Check for burned or melted connections on that fuse holder, as the fan draws a lot of current. If it looks good, then run with it, and be cool!

Thanks for the beer offer - but I'm suckin' on a pina colada right now!

Oh, and X2 about not trusting your mechanic. He should have said straight up that he did not understand how those old cars were wired...

 

yeah he could of kept it real with me but hey it is what it is. good to know theres good people on this site that dont mind steering a young buck like me in the right direction

 

and yes it was a 30 amp. something had to make it blow out besides being 41 years old so ill check all the surrounding connections and make sure theres no unwanted resistance..

 

We are all here eager to help and share experiences - that's what I really like about this family we have here!
Be sure to check the connections at the blower resistor, as they are known for burning. It is located on the lower evap case in the engine bay. The plug will have 4 wires on it. Mine was a gonner and was restored last year.

 

If you're not as badly afflicted by OCD as Rob is, though, you can just replace the melted plug and connectors with regular old ¼" spade terminals (soldered to the wires, of course) - just be sure to put the right wires on the right terminals.

- Eric

 

Back in the day when our cars were new, you had to be very imaginative to be successful. Everything (I think) GM in those years had the fan wired the way you great people painstakingly walked the member through. Today's mechanics ain't mechanics like in the old days. I know, cuz I was/am one. Today's guys are technicians. Today's vehicles don't respond to logic because of the way things are built with controllers instead of relays, computers instead of switches and so forth. But many think their stuff don't stink, and to 'fess up they don't understand something just ain't in their genes. I know because I have both mechanics and techs working for me. AND, I are one to one extent or another.
Long story short, I wouldn't just simply mistrust him and not go back. I just wouldn't bring my old stuff to him, unless you spotted an old guy with busted up hands, a limp (bad knees from setting lifts) and a definite hunch to his back in the shop. sdcarguy