63split63

The valve is brass not plastic . The hose it is designed for is plastic ( pex) . I should have been more specific .
BILL

Mod75

Thanks to all for the info and pictures.

Will tackle that project this week.

bobbarry

The assembly manual for my '71 shows a factory vacuum-actuated hot-water shutoff valve as part of the small-block A/C setup; there is no sign that the A/C on my '71 ever incorporated such a valve.

The 5/8" return heater-hose had some grooves in the outer surface from rubbing on the A/C pulley; I cut out the damaged section and replaced it with a shutoff valve for 3/4" pex hose (it fit the return hose perfectly), and the cabin is cool again. I'll fix it all right when I convert to Vintage Air...

Bob Heine

I don't know if this is actually going to work but I decided to give it a try. I bought a heater bypass valve for my big block '72. It's for a '93 Chevy Astro van. It's vacuum actuated and bypasses the heater core while allowing coolant to circulate through the expansion tank, just like it was designed to do. There may be some back eddies letting hot coolant get to the heater core so it may not be as effective as two shutoff valves. On the plus side I should be able to switch the heat on from inside the car. I usually need the heat during Florida's torrential downpours to mix with the A/C to keep the windshield clear. To activate/deactivate the valve I plan to connect it to the manual wiper door valve below the steering column. I changed to a long L-88 hood so there is no need for that valve.

MIKE80

I have a new vacuum operated shut-off valve, but since I put in my 383, the engine does not produce enough vacuum to operated the heater/ac vacuum controls. I had to add a vacuum pump to operate my brakes and it takes a couple minutes for my headlights to rise (working on changing headlights to electric). The manual shut-off valves made a huge difference for me.

diehrd

Why cant a simple hose be run from the water pump to the intake ??

AdamMeh

That's the way our '77 was when we got it. Worked fine, but I plugged off the fitting spots on the intake and water pump instead of having a loop of heater hose hanging there. Cleaner looking IMO.



Adam

REELAV8R

You could do that, or completely block it off. I didn't do that to mine so I still have the option to turn the heat on when I need it. I don't live in AZ of FL, it still gets cold in SD.

AdamMeh

That's where I'm from originally and yep, I had a heater in EVERY car I owned no matter how old

gq82

Your 71 should have the factory shut off valve however it's very difficult to see. The problem with it is it only functions when you set your AC to Max Cold which closes the hot water inlet, closes the outside air door and opens the interior cabin door in effect creating a recycle mode.

Thats how mine works.

superdave269

My factory by-pass leaked that's whyI used the brass ball valves.

BKbroiler

Mainly because it looks like crap.

Mike's 68

68's without AC do not have cut off values ... I don't know what they were thinking. I have added a ball valve but haven't been able to test it out since my car isn't put back together yet. I also repaired/restored/cleaned the entire vent system to include the doors and seals. Can't wait to get the front clip back on and go for that first drive.

gq82

Your correct your non AC 68 doesn't have the factory shut off valve but as I've said earlier the valve on AC cars only works when Max AC is selected so most of the time it's allowing hot water to enter the heated core.

A well sorted out HVAC system in a C3 should allow for a comfortable temp in the cabin without the need for home made valve installs. I never use the AC in my car. I test it in the spring, mid-summer and b4 storage. I drive in any weather in comfort without hot air coming in thru the heater outlets.

vette427-sbc

I installed a PEX shutoff valve on my heater core line (the one coming off the intake) and had issues with the car overheating when it was blocked off. Open the valve, and all is good again. That was with a stock water pump. Now I have an Eldelbrock victor water pump and it still does the same thing! How is everyone else blocking this hose without this issue?

Temp sensor is in the passenger side head, Temp gauge is a tested accurate autometer. My car will stay cool (180*) sitting in traffic on the sun with the valve open. I closed the valve the other night to test it again and it started to get hot (220*) within minutes.
The heater core is not cooling my car 30*+. I have some kind of circulation issue that no one else has

wcsinx

That's precisely why I installed a valve in the heater core line in my C5. It makes a noticeable difference in cabin temps and the performance of the AC. On my C3 I just put brass plugs in the water pump because it's strictly a fair-weather vehicle anyway.