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I have a 78 Silver Anniversary C3, original owner, and the car has 91K miles.
I hope someone can solve this mystery for me... The airflow coming from my Heater & Air Conditioning Control Panel is not working properly. All airflow is directed to the floor area on the driver side and passenger side.
Select VENT, the airflow comes out to floor area.
Select HTR, the airflow comes out to floor area.
Select DEF, the airflow comes out to floor area.
Select A/C, either MAX or NORM, the airflow comes out to floor area.
The FAN works and increases the flow, but I can't get the air diverted to other outlets.
The TEMP can be changed from cold to hot, although the A/C doesn't seem to blow colder even though I had it serviced in late 2022 and mechanic converted to the current refrigerant. It worked prior to winter, but I didn;t check it again until spring/summer.
So... Is this a vacuum problem, electrical problem, mechanical problem? A real mystery to me.
Please help.
This plastic rivet. This is the most common cause of the air only blowing down problem. Replace with a 4mm screw, nyloc nut and a couple wide washers. You can adjust the tension and the nyloc nut won't back off.
Oh, and it's a vacuum problem. The rivet is in your vacuum switch under those sliders on your console. As the link provided above shows you.
I'm late to the game here Keith, sorry.
Both the above posts are excellent advice. These vacuum HVAC switches were not one of the General's better ideas. I have a similar switch in my 1977 K-20 and I fought with it for a month before I got it to function within normal parameters.
Keep us posted with your progress
78 Airflow Mystery
