I was wondering how exactly the wiring for the blower motor works. I noticed there is a relay I am assuming that connects to the blower motor itself and also what looks like some bunched coils that are bolted on the heater box assembly. I had been removing my fender and had severed the wires to the relay and the motor quit. So I will have to find another relay (I am assuming) and wire it back up? Or would there be another way of going about this?

 

The little coils of wire are the resistors, that produce the various speeds. There are 3 of them, responsible for the 3 lower speeds.

The relay is a Form C "changeover" contact set; with a common, a normally closed, and a normally open contact. The motor is connected to the common contact via the fat purple wire, the resistor circuit to the normally closed, and a hard battery feed to the normally open. When the relay is in its normal (not energized) position, the motor gets its power from the resistors, which in turn are fed from the 3 contacts of the switch. In the highest speed, the 4th contact of the switch sends power to the relay coil; the relay is energized; and power is then supplied to the blower motor from the battery feed. That feed is a large red wire that runs across the windshield cowl above the evaporator, and ends in a connector of extremely stupid design right above the pass side valve cover, that always burns to ashes. (If you ever are in the situation that the 3 lower blower speeds work but high doesn't, it's usually that connector has burnt to a crisp and melted and no longer making contact).

So, put your dykes away, and stop hacking your wiring; repair the damage you've already done, i.e. solder and heat-shrink the wires back together; and put it all back together like it belongs. Yes you need the relay. The switch in the dash, and its wiring (which BTW contains another of the same stupid connectors, that also burns to ashes..... if you have the problem where absolutely nothing electrical in the HVAC system works, it's that other connector which in behind the dash, located about 12" as the wire runs from the "mode" switch on the control head) cannot carry enough current to run the blower in high speed without starting a fire. That's why the relay is there in the first place. And, next time you are working on something and there's wiring in the way, unplug it and move it out of the way, rather than hacking on it and making extra unnecessary work for yourself.

Very simple circuit really. Like everything else about a car. It continually amuses me how people can think that car wiring is complicated and hard to understand.

 

Glad to be one of those people...............just for you

 

LMAO

 

Yeah it's Monday morning, I'll take all the amusement I can get!!!

 

Guess I didn't make that statement very clear on my part. It had been hit on the pass. fender a while back and had caused the damage.

I see what you are saying about the coils and relay. Now if the relay isn't hooked up than 3 speeds wouldn't work correctly and the full wouldn't either.....

So when its been replaced they will work...... there is a specific relay for this correct? So would a parts store be good enough or would I have better luck at a junk yard.

 

Well put I must say....I can't count how many times I have arched a screwdriver or socket wrench on that POS connector. The relay and wires had been crushed and in order to remove the fender the wires had to be pulled out. Since they couldn't be reached. So I figured if I could........learn about how components work for the system. I have a Non-AC heater box......(for engine header clearance)

 

I'm not sure what the non-AC wiring is.... never have had one.

I can tell you however, that the way the factory does that, is that as the car goes down the production line, it reaches the point where they put in the entire HVAC system as a unit. The whole thing, with the evap housing, compressor, control head, wires, heater core and it box, ductwork, etc. goes in as an assembly. That harness that comes through the firewall and goes to the resistors and all that, is part of that assembly; and is therefore set up specifically for the AC system being installed. It might be worthwhile to locate a schematic for the car, and duplicate the factory configuration for that; the chassis-specific Chilton's for this car that you can buy at the parts stores like Auto Zone, the one that's about ¾" thick, has some schematics in it, and might have the info you need. A factory service manual obviously has it also. But both of my those are at home, and I'm at work, so I can't look at either to tell you exactly what the wiring is.

 

Well its an 89 that originally had AC but I got a non-AC heater box and converted it. Still has the same coils, (smashed) relay, and wiring. Don't know if that makes a difference......and I do have the manuals, I am at work myself. I was just wondering if I should look for a new relay or if there is another one that would work. The car has a carbed crate engine in it so that harness for the TPI is useless. The TPI was trashed.....warped intake,cracked runners, 2 broken injectors, bad fuel pump, etc.

 

That same realy is used widely, on most all GM cars of the same era; so you should be easily able to find one at the boneyard.

That AC harness, with the relay and all, is completely separate from the TPI one... remember, the AC is a unit, and the engine is a unit.... the engines come to the assembly plant on a crate, with the engine harness already installed; once the engine is in the car, they simply unroll it, install the ECM, route the harness to it, and plug it in. All that happens after the AC is installed. In general, they assemble the car body, then the glass, then the AC, then test for leaks in the spray tank; then the interior including the dash and its wiring, then the powertrain. Each of those parts gets its wiring installed along with it as the optional parts that determine what wiring is required, are added. At any points where one harness touches another, there will be a connector. For instance, in the case of the AC one, there are exactly 2 connectors where it touches any other wiring: the brown wire under the dash that brings switched ignition power to the control head, and the big red wire that carries battery to the relay.

 

Oh ok, didn't know they were seperated harnesses. I'll have to check out a yard for one I guess. Thanx for the info.

 

You can really learn ALOT about cars in general by seeing how they're put together. There are things you don't even know that you don't know, that you'll learn by watching the process. I think every car hobbyist should go visit an assembly plant that gives tours. In fact, I think every mechanic should too, because then they'd understand better how to take it apart and work on it. Just like I think every design engineer should be required to (a) use the product they design, exclusively; and (b) spend time in the field servicing it. Fat chance of that But anyway, in the case of the hobbyist, seeing the order that cars are put together in, and what the chunks are, and that sort of thing, is of incredible value when it comes time to work on major systems like that; or even doing simple things sometimes, just to know where they break apart into their component parts.

The Corvette plant in Bowling Green KY is perfect; they give tours where you walk right along the production line, watching a car get built. Granted, it's somewhat unique, being a Corvette and all, but you can see right there in front of you, the "modules" that the car is made up of.

 

yeah that always fascinated me when I saw that stuff on TV. Not the same as being there.....kind of like when I was at the Budweiser plant in St. Louis as oppose to seeing it on TV

 

the budweiser plant is only about 40 miles from me and its quite interesting to go thru isnt it .....

 

You know it