When I got my '80, all the heater hoses, etc. were missing. I'm in the process of replacing the hoses but I don't know if there should be a heater control valve or not. If so, is it vacuum operated?

Also, is there any way to check to see if the heater core leaks, without plumbing it through the regular hoses? I don't want to flood the interior in case it leaks.

Jack

Mine did have the vacuum operated valve which is intended to reduce in cab temps on warm days. The real question is do they work and are they worth the hassle?

To test your core, hook up a 6 foot section of hose to both nipples on the core. Then, using a ladder, elevate the ends of the hoses as high as possible to create some pressure while filling them with clear water. You may want to flush any residual antifreeze out before doing the test to keep it out of the carpet if it does leak.

I believe all have it. Even the Haynes manual barely mentions it as a 'heater water valve' instead of a heater control valve. Most are vacuum operated on gasoline engines nowdays. Manual opening and closing is common for diesels. Some engines have it mounted in the manifold...etc. Your 80 should have one..V8...That is inline from the heater hose out of..well into the manifold. Not the one from the top of the water pump. It will have a tiny vacuum line to the controls inside the cab. Hope I haven't confused you more than myself...lol

How about a photo?

http://www.autozone.com/autozone/parts/1980-Chevrolet-El-Camino/Heater-Control-Valve/_/N-ilz7sZ91sh0

Jack,
Yes it should have a water control valve inline in the heater hose. When you put on the A/C, the control switch in the cab will shut off the water flow through the heater core so you get unheated air to the Evaporator in the cab for coolest air. If you would send me a PM with your email address I will send you an email with the vacuum diagram for the climate system. It will show you where and what color the vacuum line to the valve is all about. I can also post a photo of how the valve is located but it will be a day or two to get the camera charged up and get thru the snow to the shop.
Craig

The older Elcos without AC didn't have a water valve, but maybe the 5th gens do.....

The vacuum line that controls the heater valve is gray. The source vacuum that goes to the control head is purple. The first picture is the original heater valve on a 79 El Camino located in the front right side of the intake manifold. The second is an original heater valve on a 86 El Camino.

http://i563.photobucket.com/albums/ss74/EddieG-3/100_0294heatervalve.jpg

http://i563.photobucket.com/albums/ss74/EddieG-3/100_0362heatervalve.jpg

Thanks. What's that other vacuum thing to left rear of the carb?

Jack

That other thing is the EGR valve.