And I'm not referring to our esteemed political leadership in Washington
with that headline

What I AM asking for is advice/directions on how to try to get the
ventilation system in our '78 working. Now that I've got a fairly good
handle on the fuse panel (thanks again, Joel and Mike), I need to figure
out why the heater/AC fan isn't blowing.

What would be great is if somebody could suggest a logical plan of attack
on this problem. The fuse itself in the panel appears OK. I'll change it out
anyway, just to be on the safe side. But if that doesn't solve the problem,
what would be the next item to check? The switch in the console? Then
the blower motor itself? If I'm not mistaken, I believe there's a blower
motor relay involved in the system too?

I have a multimeter, and I'm not afraid to use it (although some expert
guidance on applying that tool in this situation would be very welcome).
Right now the A/C system isn't operable, and I think I'll probably need to
do some work on the heating system as well. But I'm not worried about
not having hot or cold air--I'm in California, so neither is essential right
now. What I do want/need to do is get the fan blowing, so we have some
ventilation in the cabin.

As always, any assistance will be very much appreciated!

The wiring diagram does not show the '78 to have a high-speed blower relay.
It shows the blower switch getting 12v from the A/C fuse. From the switch, the power goes to the heater resistor, which controls the speed.
So, either the switch is not getting 12v from the fuse, the switch, resistor, or the blower motor is bad.
Check for 12v(key ON) at the brown wire at the switch first. Then, with the switch on "High", check to see if you have 12v on the orange wire at the switch. The orange wire goes directly to the blower motor(and the resistor), so if there is 12v at the switch, there should also be 12v at the blower. If you have 12v at the blower, check to make sure the motor(blower) is grounded.

And there's the road map I needed to pursue--and hopefully solve--this
particular problem.

Thanks--yet again, Joel--for illuminating the way to fresh air (and
ultimately, actual cold and hot air as well)...and helping get this sad shark
back in shape.

Now where's that multimeter of mine...

Check the simple things. Is EVERYTHING plugged in? Do you have an aftermarket radio which would suggest that someones been messing around in the vicinity of the heater controls? Checked some previous posts of yours to gain some insight. Seems your heater hose cutoff valve has been removed? Maybe the previous owner also didn't want the blower running all the time(it does) and pulled the wire at the blower down between the fender and A/C housing. The high speed relay is right on top near the alarm switch. Pull the plugs and check the contacts. Maybe run a wire from the "bat" term at the alternator directly to the blower motor to see that the blower is good and has ground. The ground should be at a bellhousing bolt down by the starter. Someone change out the starter at any time? Maybe the same guy who broke your ground connection at the A/C compressor also broke it at the starter.  Mike

Joel, the wiring diagram in my 78 serv. manual doesn't show the high speed relay. Pretty crude diagram, didn't check in my separate wiring diagrams, tho. 79 manual shows it correctly including wire colors. Much better detail. I recommend anyone with a 78 get a 79 manual, only a few differences but when used along with the 78 manual really clears some things up. 79 manual is ALL Corvette, not all Chevrolet like the 78 book.  Mike

Great advice and directions, Mike. I'll follow through on your
recommendations. Some PO really wanted to stop most of the equipment
on this car from working, from the key buzzer to the AC to the alarm,
antenna, heat, and on and on. So it won't surprise me to find yet another
nasty surprise like these lurking someplace under the dash and/or hood.

The radio is gone. It doesn't appear that any aftermarket version was ever
added either--I haven't found any tinkering with the speaker wires, and
with what I think is still the original factory harness. What the PO did was
unplug/remove stuff. Fortunately, they left some it in the car, just
disconnected.

Other items, like the vacuum hose to/from the hot water valve, have been
damaged. The valve's still there, but the small vacuum hose coming from
the firewall was cut and a section of it is gone (that'll be the subject of
another post, to ask for help in finding out what size replacement vacuum
hose I ask for at the parts counter).

The starter looks old, so my guess is that it might even be the original. I'll
get under there and check on the presence/condition of the ground wire
you describe.

Hopefully, with your and Joels' help with this puzzle, I'll find the
answer(s). Meantime, many thanks for all the info--

[QUOTE=mkapp7879] Joel, the wiring diagram in my 78 serv. manual doesn't show the high speed relay. Pretty crude diagram, didn't check in my separate wiring diagrams, tho. 79 manual shows it correctly including wire colors. Much better detail. I recommend anyone with a 78 get a 79 manual, only a few differences but when used along with the 78 manual really clears some things up. 79 manual is ALL Corvette, not all Chevrolet like the 78 book.  Mike[/QUOTE]

I just checked, and I don't show the high speed relay(even tho I know it's there!) until 1980 in the service manual diagrams!!! They also don't show the A/C system as a separate diagram. I'll have to check in my Mitchell books and see if they have it on their diagrams!
Thanx for pointing this out, Mike!

I have been having a similar problem. I hot wired the blower motor and it appeared to be bad. Of course Auto Zone tested it and said it was bad. When I first got the car it seemed to work on the lower setting but not the high setting. I put the new blower in last fall and it was working. Then this spring I see the same problem, with the new blower motor. I did remove all the A/C parts (for looks and weight) and I have some wires going not hooked to anything. All I really need is the defroster in the early spring and late fall. Could this be the problem?

thanks for any help.....