Late Model C3 - Is the Blower Fan on Low anytime key is on?

BBShark

Garage Monkey
Staff member
Joined
Mar 5, 2008
Messages
4,671
Location
Right here
I converted my HVAC system with parts from a 79. This included a new, stand alone 1979 AC wiring harness.

I am working on the console now. So, a couple of days ago I tested this setup. It seems to work but, anytime the key is on the blower fan is on at low speed. I went over the wiring for this and it sure looks like that is the way the system was designed. The "heater" wire from the fuse block goes directly to the blower fan resistor. I have been trying to figure out what is wrong with this for two days.

I don't know if this is correct but, I saw a Youtube video where someone said that all C3's after 1975 worked like this. If correct, what would be the purpose of doing this?

At 13:00
 

rtj

Well-known member
Joined
Nov 5, 2011
Messages
2,653
There appears to be a big thread at CF.

I’m not surprised. Wiring the wipers was goofy on the 75 the way they did 2 speeds. I put in a toggle and accepted 1 speed as the car can’t really be driven in rain. :)
 

BBShark

Garage Monkey
Staff member
Joined
Mar 5, 2008
Messages
4,671
Location
Right here
I'm OK with the fan being on low when you select a mode like heat or vent, etc. But I don't get why it's ON low when it's in the OFF position. I have no idea what the logic/advantage is there.

Yeah, the wiper setup is nuts. I use 2 switches, 1 on/off and 2 momentary. I don't really see myself in a downpour either.
 

rtj

Well-known member
Joined
Nov 5, 2011
Messages
2,653
If you search the CF thread, they discussed why the fan is on. I read some and some explanations seemed to have merit. Or, could be BS.

Link:

site:corvetteforum.com heater fan always on

Punch that into your search engine and you’ll get a bunch of hits.
 

BBShark

Garage Monkey
Staff member
Joined
Mar 5, 2008
Messages
4,671
Location
Right here
I did find that some people were complaining that the air box (inside the engine compartment) picks up heat from the exhaust manifold. I have a big block car and the headers actually burned a hole in the box. When I put the car back together, I used an AC box from an 81. No way to fit it with a big block and headers. So, I cut it up and made clearance and heat shielded it.

That makes sense that the air would pick up some heat from the "hot box" and then heat up the air in the vents. But, was GM's "fix" for this to have the fan on at all times so that it internally cooled the box? Pretty lame solution.

That's the only thing I can come up with.
 
  • Like
Reactions: rtj

BBShark

Garage Monkey
Staff member
Joined
Mar 5, 2008
Messages
4,671
Location
Right here
I figured this out! So, the fan is on anytime the ignition switch is on, even when OFF. Found a switch position that feeds voltage to the other switch positions. Put a relay on that and turned the fan OFF when OFF!

This is the kind of stuff that causes serial delays in actually putting this car together
 
Last edited:
Top