'72 rewire, especially the AC harness

[19brownie92]

I just finished an complete rewire on my '72. I used a "upgrade kit" so it replaces the panel with blade fuses and a few other niceties. My problem is this;
The kit did not come with a new a/c harness. Mine is in good shape so its was no problem. It a pretty much stand alone harness anyway.
The new dash harness had a Brown wire that replaces the factory brown wire in the blower switch. As far as I can see this is the only place the A/C harness connects with the dash harness.

In my old configuration there was/is a heavy orange wire that came from the A/C harness to the fuse panel and was plugged into a blade connector. (no fuse) I assumed it was the power feed for the A/C harness.

I am not convinced that it was the factory config. but it all worked. On the new harness I connected the orange wire to power and nothing on the heater/ ac works.

I was looking at the diagrams on the forum and it looks like the orange wire (14OR) goes to the blower.

Any help would be appreciated.

[19brownie92]

I found the problem with the blower. The Brown wire from the new harness had pushed out of the connector. I put it back in and the blower now works but not on "high"

I have checked the relay behind the glove box and found a loose ground. when I ground it properly the fan does nothing on high. When it is not grounded the fan will blow at a low level when on High.

The relay does seem to be working, it will "click" when the ground is interrupted. But no "high" blower.

[iriereggaeman]

Hi 19brownie92,

Maybe you got this figured out already, I had the same problem with the blower running on low, and medium, but not high. (Actually, on high, the air would peter out slowly)

I first tested the fan connecting it directly to the battery (getting that out from under the hood hinge was a PITA)! Connected directly to the battery, the fan spun to high-speed life.

Then, I tested the dash switch by removing the connector, and jumpering the low, medium, and high connectors. I saw the same behavior, low and medium worked. High did not (can't be the switch).

After reading many posts on this forum about checking the blower relay, I thought I'd give it a look. As indicated by others, the relay was located behind the glove box for my '72 Suburban. I jumpered the socket between the brown and yellow wires, and again, the fan sprung to life. Even still, I hesitated to buy a new relay after looking at it. It looked brand new! (see pic) Running out of options, I purchased a 4Seasons 35760 relay (Amazon), and awaited its arrival.

I'll be damned...it did the trick! My blower is now fully functional. Hopefully this helps you, or someone else with similar symptoms.

Here's the existing / "old" relay. Looks new, doesn't it?!


replacement relay installed. Not sure what the existing ground wire(?) was for. It wasn't attached to anything. (The relay is grounded)


Part number

[19brownie92]

Originally Posted by iriereggaeman

Hi 19brownie92,

Maybe you got this figured out already, I had the same problem with the blower running on low, and medium, but not high. (Actually, on high, the air would peter out slowly)

I first tested the fan connecting it directly to the battery (getting that out from under the hood hinge was a PITA)! Connected directly to the battery, the fan spun to high-speed life.

Then, I tested the dash switch by removing the connector, and jumpering the low, medium, and high connectors. I saw the same behavior, low and medium worked. High did not (can't be the switch).

After reading many posts on this forum about checking the blower relay, I thought I'd give it a look. As indicated by others, the relay was located behind the glove box for my '72 Suburban. I jumpered the socket between the brown and yellow wires, and again, the fan sprung to life. Even still, I hesitated to buy a new relay after looking at it. It looked brand new! (see pic) Running out of options, I purchased a 4Seasons 35760 relay (Amazon), and awaited its arrival.

I'll be damned...it did the trick! My blower is now fully functional. Hopefully this helps you, or someone else with similar symptoms.

Here's the existing / "old" relay. Looks new, doesn't it?!
Attachment 1703964

replacement relay installed. Not sure what the existing ground wire(?) was for. It wasn't attached to anything. (The relay is grounded)
Attachment 1703965

Part number
Attachment 1703966

So I did figure it out and I feel really stupid. I had been working a bunch of nights so I wasn't thinking very clearly. After replacing the switch and the relay. I discovered that the "power source" I had the heay orange wire connetes to did not have power. I had just put in an American Autowire system (amazing by the way, highly recommended it) and I was using the Aux plug and had the wire one hole off on the connection.
Lesson learned....get more sleep!!
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