While I'm flushing, evacuating, and recharging my A/C system I decided to add another vacuum controlled heater valve to my existing system. I currently have an isolator valve which has four 5/8" nipples, two for the heater core, and one each for the water pump inlet and intake outlet. The purpose of the current valve is to allow water to flow through the heater core until a vacuum is applied to the valve, at which time the heater core is blocked off and coolant is directed to flow from the intake manifold directly to the water pump, thus bypassing the heater core.

This system works great since it isolates the heater core so that heat can not move along the coolant like with single shut-off valves. But, after thinking about it there is a draw-back because coolant can now circulate from the intake manifold directly into the water pump without getting cooled down through the radiator. So, I'm installing a shut-off type valve along with my current valve. I looked at the OEM style valve and it's made of sheet metal and has a 90 degree bend between the inlet and outlet nipples. If you want to see a picture click here: http://67.116.80.82/Vette/Files/OEMH...ntrolValve.jpg The counter person at Autozone helped me look through some of the heater cores in the back and I came up with better one made of black plastic that has parallel inlet and outlet nipples, but it has a 3/16" vacuum connector instead of the 1/8" as the OEM...simple solution was a 1/8" 1/8" 3/16" vacuum "T" to splice into my current vacuum line. If you want to see a picture click here: <A HREF="http://67.116.80.82/Vette/Files/ImageOfPart.jpg" TARGET="_blank"> http://67.116.80.82/Vette/Files/ImageOfPart.jpg</A> The part is a Factory Air brand part number 74803 Heater Valve. and costs like $15.

If you have A/C then run a vacuum line using a 1/4" 1/4" 1/8" vacuum "T" from the TAN striped vacuum line coming from the vacuum control in the center console out the firewall (there should be an extra hole where the line can run) over to the heater hoses. With this setup the Off position, A/C circulation, and A/C max settings will shut the coolant AND HEAT off from entering the heater core. All other settings including the Bi-Level setting will open up the valves and allow heat and coolant to flow through the heater core. With a well running A/C system and blower the controls can be set to Bi-Level all the time and temperature set with the temp control on the center console, but when it gets 100 degrees and I need extra frosty air I can set the control to A/C max and maybe get ice cubes out of the vents.

On a side note I was almost worried about isolating the heater core in case the water expands and busts out of the heater core. But, after checking everything I see that when the car is just sitting in the winter the valves will be open and pressure will exit via the radiator cap (unless you have a thermostat in which case the coolant will need to sneak around the water pump (unless it's frozen)). Also if I've had the system on Bi-Level and decide to switch to A/C then there will be hot coolant in the heater core which could expand, but of course the A/C will be on and actually cool the heater core down...so there won't be any risk there. Nope...I think the combination bypass and shut-off valves will be my final adjustment to my cooling system. That is until they make a thermostat that can open completely after engine warm up and stay 100 percent open until the engine is shut off.


[Modified by Rockn-Roll, 8:06 PM 6/2/2003]


[Modified by Rockn-Roll, 8:07 PM 6/2/2003]