I have a 78 ..can anyone tell me where to start looking ..vacuum line or diaphram..as to why my blower is diverting air to the floor ducts when i am in the vent or a/c position..thank you

Do you hear vacuum when you move the dash control lever? Possibly disconnected under the hood at the feed line, or the feed line is broken due to heat (old hoses). The system runs from the engine, to the valve assembly at the control head, and then to individual vacuum motors to operate the doors. If you have the FSM (Factory Service Manual) that will give you all the diagnosis info.

in the transmittion tunnel, on the right side front, there is an adjusterment you can make in the line itself.

While you're checking things out (like the cable adjustment under the console panel on the right side as mentioned by "blahbored" above), make sure you give all the return springs on the actuators a stretch. If they've been sitting for a long time, they accumulate enough light rust to prevent them from moving, hence no vacuum acutation.

My symptom was hot air blowing when the A/C was on. Stretched the springs, and now they work perfectly. Unfortunately I broke the High Pressure A/C line at the compressor manifold:doh: , three days after enjoying the "spring stretch" cool air and haven't had A/C since. Gonna have to replace almost everything, but hey, that's what owning a C3 is all about anyway!:thumbsup:

Metalkid:rockon6rk:

My 1980 does the same thing, I took the dash totally out of the car at the begining of the summer and traced every vac line and could not find the problem. Hooked up a suction gun to the main line and everything looked to work fine. Drove car all summer and never used the air so if I wanted it to come out the heater ducts I switched to Vent and out the vent ducks I switched to heater.

Someone before me has played with all the vac lines under the hood, I believe that because you can lift off the factory air cleaner and there are no vac lines that go from the manufold to it.

Has anyone got or seen a diagram for the vac lines under the hood, I have one for Air and Lights but not Smog? or Carb.

Thanks
Mike

Someone did say in the know (Vette Machanic) that low vac presure could cause that to happen.

Thanks for the vac lines diagram, it is what I was looking for.
As soon as April is here and the Vette comes out of storage, the Vac lines are my first job.
Mike

My 1980 does the same thing, I took the dash totally out of the car at the begining of the summer and traced every vac line and could not find the problem. Hooked up a suction gun to the main line and everything looked to work fine. Drove car all summer and never used the air so if I wanted it to come out the heater ducts I switched to Vent and out the vent ducks I switched to heater.

Someone before me has played with all the vac lines under the hood, I believe that because you can lift off the factory air cleaner and there are no vac lines that go from the manufold to it.

Has anyone got or seen a diagram for the vac lines under the hood, I have one for Air and Lights but not Smog? or Carb.

Thanks
Mike

Someone did say in the know (Vette Machanic) that low vac presure could cause that to happen.
with my big cam my motor only has about 9-10 inches of vacuum, and my A/C still operates properly so probably not low vacuum more likely no vacuum a line split or disconnected somewhere would be what i would look for

Thanks for the input, I think you are probably right about no Vac pressure Vs Low Vac pressure.

Mike

Thanks for the vac lines diagram, it is what I was looking for.
As soon as April is here and the Vette comes out of storage, the Vac lines are my first job.
Mike
Could you put the vac lines diagram on line for all to see, I think I may have a similar problem.

Father/Son

Not sure how to do this?

If it is not attached to this send me a e-mail and I will send it to you that way

Mike