On my '83 G20 van w/ 6.2 NA diesel, air is coming through the dash vents regardless of the a/c or heat system being on or off. Could this cause the a/c system to "underperform"? Thanks to all that replied to my prior post re: a/c underperforming.
It is normal for a small amount of air to come out the vents,this is do to GM's fresh air system.It is designed to keep fresh air circulating through the cabin to help keep the driver more alert & humidity down.The temperature of this air is regulated by your temp. control lever. It will not affect the heating or cooling system.
You might be able to mount another switch in-line on the blower motor power lead. You could mount it somewhere in the cab where you could reach it fairly easily. Otherwise the blower is always on as Bandit said.
Thanks for the great idea. However, I don't think the blower is actually on because it stops when the truck stops (if I recall correctly from the comfort of my house. I'll have to check tomorrow.) If I'm right about that, it would indicate its just a vent open somewhere, correct?
The problem is that the blower motor control switch has no "off" position. When you turn the key on, the blower comes on really low. As was said by others here, GM had it's reasons, and the only way to stop it is to add a toggle switch to shut off the power to the blower completely. I found out something else when I did my heater core. I got a new blower motor when i did the core, figured I'd start fresh... The motor I got, only works on Hi or Lo, it doesn't work in between like the old one. I was too busy to exchange it, and didn't discover it until weeks after I replaced it. When I put it in, I put it on Hi to test it, it worked, and I parked the truck until I had to plow, then I discovered this. Even though I lost the in between settings, it still runs all the time like everyone else here. It seems like I use it on Hi or not at all anyway, so I can live with it