Air Conditioning Blower Wiring/Vacuum Diagram

[firebirdparts]

Welcome back to Post-crash TAC!

About half the electrical problems we have are related to the A/C blower, so here's the famous sticky thread we all know and love.


And here's an extra one

[firebirdparts]

The wiring diagram requires a little interpretation.  Here goes:

The a/c harness is a separate harness that was not used on heater cars.  The standard wiring harness on the car has a heater power wire coming from the heater fuse through a dedicated set of contacts in the ignition switch.  This wire plugs into the a/c harness around the area of the controller.  It's brown.

Power from the heater fuse powers the compressor and the first three fan speeds through the fan speed resistors.  One of these wires (giving low fan speed) is hot at all times when the ignition switch is on.  When I say all times, I mean all times.  There is a little box of a relay on top of the evaporator, and when this little relay is unpowered, it connects the resistors to the blower.

When you put the blower on "High" the blower switch sends power to the relay.  When the relay is powered "On" it connects the blower to a red wire that comes straight from the back of the alternator.  This wire runs hot and it's pretty common to have a bad connection where the engine harness connects to the a/c harness.

Last but MOST IMPORTANT.  The a/c housings are plastic.  The blower itself along with the relay and compressor were grounded through this a/c harness.  The ground wire on most firebirds was bolted to the a/c brackets.  Thus, when Uncle Rico discards your a/c brackets, you will disable the blower.

[Wallington]

Also, if you've owned the car more than a day, go out and buy the factory manuals. Saves a lot of asking mundane lazy questions. If you still get stuck, post it up. Electrical is easy to get stuck on.

[DeVilliers]

Hi guys,

I'm a bit stuck.
I'm assuming that I am missing a relay at the end of this plug. The car had aircon at some point. All that was ripped out by the previous owner.
So I have put back the blower motor as a minimum, no aircon.

2021-03-19_12-05-07 by DeVilliers Buys, on Flickr

The orange wire seem to be tied up with the rest of the wiring, but is it not suppose to be going to the blower motor?
Would this be the correct relay?
https://www.rockauto.com/en/catalog/pontiac,1979,firebird,6.6l+403cid+v8,1250570,electrical-switch+&+relay,blower+motor+relay,3088

Help please.

Thanks

[firebirdparts]

This is the whole system.  I was thinking that plug connected two parts of the system to each other, but I don't know.  The important thing is that's not the relay plug.  the relay doesn't accommodate any extended locking part like that.
Under hood

under dash (two different cars shown here)

[jbanna]

I agree, but get the service manuals - they are now available online for free (sorry, you'll have to find the URL); I struggled with blower motor problems off and on over the years, and I hadn't changed any of the original setup, so with a vehicle having the A/C ripped out, I recommending trying to find the parts and just start over - I did that with my 77 F-150, whose previous owner had not only removed the factory A/C, but also converted the HEI ignition to a points one...both of those decisions were absolutely stupid and I don't know why it was done because the truck was in a used car lot when I bought it in '87.  Fortunately, I corrected those problems in the next few years at comparably low prices, returning to the stock systems, and have not regretted it to this day; in fact, my A/C is still ice cold, and the ignition system has been trouble free...