1978 Corvette broken vacuum lines?
 

Hi All, looking for some input here. While going over my newly acquired Pace Car's engine compartment, I came across a yellow line/tube that has broken. While taking some pictures tracing this line into the firewall I then also noticed two other electrical wires with damage in the insulation. Looked through the service manual I have here but can't positively identify either. I'm still in my first week of corvette ownership, so this might be an obvious question: What are they for and what are they called? I should add that my Air Conditioning is not working and I believe neither is my heater. when I turn the ignition on I do hear some sort of motor/fan powering up, but there is no noticeable airflow from the vents. Not even sure if that motor/fan is supposed to come on or not. I can't turn it off. Any chance that these issues are all related and all my AC/heater problems will be solved when I replace these?

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The yellow tube where it connects in the engine bay.
https://cimg8.ibsrv.net/gimg/www.cor...520c70046b.jpg
At the firewall, note the two damaged wires
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the cut off yellow tube.

That vacuum line controls the heater valve which controls the flow of coolant to the heater core. The valve is either open or closed. When the A/C is switched to Max Cool and or the temperature lever is slid to Cold the flow of coolant is shut off to the heater core.

Thank you! I'll start by replacing or repairing this one and see what that does for my climate contol.

On a 78 you cannot use the fan control switch to turn off the fan. It always stays on a very very low setting. Not sure why. As you get more into the car you most likely will find lots of nasty stuff in the compartment where the fan housing is and the inner fender that leads to it. Welcome aboard and there are no dumb questions. Sometimes some dumb answers but no dumb questions. We are here to share what we have all learned since we got our first vette. :thumbs:

Those nylon vacuum lines get brittle with age and engine compartment heat. It most likely just snapped off. Repair by using a rubber vacuum line that fits over it snuggly. Hopefully that old hot water shut off valve still works.
The fan runs on low whenever the car is on. It is very low so likely you won't feel anything at the vents. Turn it up to higher settings. If the car isn't running you have no vacuum so it will blow in the default setting. Which is the heater setting. Put your hand down behind the radio on each side. Just in front of the end of the console side. You should feel it blow there.
Once you have vacuum, car running. When you select vent, or air-con it should switch up to the center vents.
on defrost, up.
Now if that doesn't work. Well those vacuum switches are known to break the plastic rivet that holds them together.
getting a bit ahead here.
Get that line in the engine compartment fixed and then check the system. Remember, you won't feel air out of the center vents without the car running.

Thank you for the quick responses. I'm learning a lot here. I have some heat shrink wrapping and try a temporary fix so I can check the rest of the system and see what else I need to order to get it up and running again. My list for zip-corvettes.com is steadily growing. I've already found the RH duct from center RH dashboard vent is missing as well. Found that on ebay.

Pickup 2 or 3 feet of 1/8" I.D. Vacuum hose from your local autoparts store to patch the broken lines. Cheap fix for initial troubleshooting...

Just a FYI, the control valve just sits in the hose and is not attached to the fender

Those 2 damaged wires-are they the starter extension harness? Maybe someone slit the insulation for a test light? I have a pic of the starter harness. It plugs into main harness up on the firewall close to hood alarm switch. Am working on a 78 PC replacing all wiring and vac hoses.

https://cimg9.ibsrv.net/gimg/www.cor...b055ddcc7f.jpg
78 starter extension

https://cimg9.ibsrv.net/gimg/www.cor...5444d85cde.jpg
You know what, I think you may be onto something? I broadly traced the wires yesterday and they indeed seem to go between the firewall and the starter motor. See picture of the other end of that harnass. Today I experienced a rather troublesome event that I was just about to start another post on: We took the car for a scenic drive along the coast, parked the car along the beach, turned off engine, then decided to restart to re-park a bit further up: nothing! No click, nothing. All other power just fine, windows, etc. Fiddled with the ignition key, moved gear lever from park to drive, back to park, and neutral....nothing. After 10 minutes of silently cursing and reassuring the wife all will be fine, I tried it one last time without having fiddled any more since the last 'non-start' and vroom, it started in one go. Drove straight home, parked in the garage and replicate the issue again, but started first time every time, making trouble shooting rather difficult. the battery is not great, but still good. Could the wire issue and the starter motor problem be related? Or perhaps any other clues to what might cause this? Faulty neutral switch comes to mind?

"Heat Soaked" starters seem to be a common theme on C3's, I've noticed. Don't want to work until engine & starter have cooled off. On my 78, a prior owner or mechanic had crudely wrapped the starter with some kind of fabric insulation.

That is so interesting. I Have never even heard of that but it might fit the description. We'd done about 1 hour of low speed cruising up and down the cliffs on our mediterranean coast and the engine, while all indicators were normal, did pack a lot of heat when I opened the hood. I'll look into this some more. Since we're likely to have many more outings like this, the problem may repeat itself. I'll read up on it. Maybe replace the starter with one that doesn't suffer from this. Thanks!

As RICK M mentioned the starter extension harness is a known issue. The plug has a tendency to melt over time. A lot of people just cut out the plug and connect the wires together. My understanding is that it was designed to make the assembly of the car easier for the factory. Check that out while you are down there looking at the starter. :cheers:

Latest update on the Heater shutoff vacuum line: as it had snapped near the valve I was able to reconnect the remaining old line to the valve for now. Tested the system and all seems to work as described above. Good airflow in all settings and heat but no cold air though, just 'coolish'. System is still original with R12 refrigerant so I guess time to convert to R-134a.
I did come across another weird issue though: when I flip the rear window defrost switch, the AC/Heater system goes off. Anyone ever heard of this? Not a huge issue for me right now as the car won't see weather that would require the defrost to be used.

good luck..
i would post each issue you have specifically in its own thread with plenty of pics.. i also find for researching example google c3 corvette hot water shut off valve.
Here s my hwv thread and heat mitigation
https://www.corvetteforum.com/forums...e-79-w-ac.html

if you are sure r12 and sealed you can still get r12
https://cimg6.ibsrv.net/gimg/www.cor...772826d67.jpeg

thanks for pointing me to your thread. Very interesting reading. Lots for me to look into. We have SoCal/Arizona climate here in Spain ('its a dry heat') ,and cooling the car is more urgent then adding heat. The reflective shields and wrappings seem easy enough to apply. Once I have the AC recharged (will have to be converted as R-12 is prohibited here) I'll see how performance is. Could you give me more info about the brown wire you disconnected to stop the low fan blowing continuously? I don't see the point of that. Off should be off. Depending on results I may consider one of the suggesitions to bypass the heater all together and just have AC.

The point of it. (fan running on low always). As it was explained to me many years ago is.
In the 1950's and 60's it was common for the commutator in the blower motor to develop a "flat spot " when the car was used for many months without turning on the blower motor. Or in some cases the copper strip's of the commutator would corrode green. And thus when bad weather finally came. The motor would not run.
Thus GM found if the motor ran on low all the time the car was on. These issues didn't happen.
The low speed setting is so low that you can't even feel airflow at your vents. Yet some feel the need to undo this fix. Your car.

The above makes sense about the commutator, I was told it was designed that way to allow fresh air to enter the cabin...
Removing the Brown wire from black plastic connector of the Blower Resistor will eliminate the blower fan running at LOW speed, because it is a direct circuit from the A/C Heater fuse the now exposed terminal must be insulated with vinal tape of some heat shrink tube as it is HOT with ignition switch ON...
Circuit 50 is the Brown wire "arrows pointing"
https://cimg9.ibsrv.net/gimg/www.cor...5b86b954df.jpg

Great Info, thanks for chiming in and sharing the diagram and description. Much appreciated.

For the non ac people it is the lower wire that controls the fan. Remove the connector and no fan. It is hot when the key is on like Bmotojoe stated so cover it

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