I pulled and reinstalled the engine in my 70 GS 455 with AC. When first testing the car, I did not have the negative terminal off the battery grounded properly and the ground strap on the back of the engine smoked for a few seconds. I corrected the ground and everything works but the low/med/high fan speeds. Max works fine. I swapped the fan relay, but that didn't fix it. Any ideas on what to check next?
I thing there is a plug in resistor that is the controller of the speeds. Not 100% familiar with your car, but I think this is usually on the firewall in the engine compartment. Probably let the smoke out.
I checked the fuse marked HEATER in the fuse block, it was good. I replaced this relay. Didn't fix it.
No, it's a resistor. Some of them are mounted into the blower box in my experience. Here is an example that I pulled from the web. Not saying this is it exactly... https://www.ecklers.com/1968-1971-b...P7T54fE9BpWGiThBBQGSYJXbjQ6mSObxoC1KgQAvD_BwE
I apparently tugged too hard on that harness when I dropped the engine in. Found it unplugged. Once I plugged it back in, I got all the fan speeds to work. Thanks everyone!
When you put the fan on "HI", it bypasses everything and puts 12v right to the blower motor. Do all the other speeds work in the right order? You can put the fan switch upside down. So HI would be off. Jump out the switch first. Brown wire in is 12v. Black/ orange is HI to motor. Breakout the DVOM!
Check the wiring and the resistor assembly on the A/C box. Maximum speed is controlled by the high speed relay on the firewall. The other speeds are controlled by the resistor assembly. Check that yours is connected. https://www.ecklers.com/1968-1971-buick-gm-a-body-blower-motor-resistor-with-ac-53-864451-1.html
Yup I have the 3-speeds low, medium and High. When I click it to max the blower shuts off. I can hear the A/C relay click. Please note A/C compressor is out of car. Dash is apart as I’m slowly fixing items behind it. I don’t recall if certain conditions require the MAX blower position to work. As Larry said it’s time to breakout the multi-meter.
That's the high speed relay almost dead center of the firewall. https://www.rockauto.com/en/catalog...trical-switch+&+relay,blower+motor+relay,3088 https://www.rockauto.com/en/moreinfo.php?pk=38991&cc=1379763&pt=3088&jsn=412
I think I found the issue. Looks like I have a plug the needs connected. See photo. I replaced the engine harness years ago and never reconnected. However I guess I need to peel back the tape to get the plug in the harness to reach. Relay needs a main power source right!!!
