Neo Fender

The purpose of this thing is to provide vacuum, to control airflow through the upper and lower vents, yes/no?

Does this mean that vacuum exist only when hot coolant is flowing through the heater hose?

If the car is cold, how is airflow controlled?

My blower only sends air through the lower vents. I'm assuming this is being caused by the broken piece of tubing that once existed between this valve and the firewall, yes/no?

Someone installed a shutoff valve on my '79. If this shutoff valve is closed, does that mean that the HCV will not work?

Kevin_73

The heater control valve is usually a vacuum controlled valve to shut off the water flow to the heater core. GM did not put these on all years of corvettes. It sounds like a previous owner installed a manual valve shutoff valve on yours (which is fine), so that probably means that either your car didn't have a heater control vavle from the factory, or that the factory one broke and it was replaced with a manual one. If there was one originally installed on your car there would be a vacuum line coming from the controls in the console and passing through the firewall (and it should have been plugged).
There could be several reasons why you can't get air to flow through the upper vents, it could be a vacuum leak, it could be a bad vacuum actuator on the air register (behind and above the center console), it could be a broken door or pushrod in the air register, or the vacuum selector valve in the console could be bad.
Bubba worked on my 73 at one time and it looked like he removed every single air box, duct, door, and valve with a crowbar. There was not a unbroken part in there. I ordered a seal kit for the heater box and fixed all of the parts as I took them out. It sounds like your best bet is going to be to do the same thing.

Kevin

john's '81 mouse

Installation of a manually controled shut off valve on the heater core inlet line will, when closed, simply prevent hot engine coolant from circulating through the heater core, and thusly you will not get any heat from your interior heater when this valve is closed. Operation of this manually controled valve will not affect any other HVAC system operation. So if you have parts of your HVAC system which do not work, you have a problem somewhere, like a leaking vacuum line which you identified.

rdrman

I"m in thre same boat as you.I ordered the vacuum line kit.Will be installing it this weekend, I have found some lines pluged. Vacuum filter for the system was also found to be in bad shape as was the check valve that the system shares with the headlights,You might want to check these out too! :cheers:

Neo Fender

Thanks for the gouge, everyone