Where is this valve?

[mfendley]

The 77 GM service manual shows this vacuum diagram for the vette, and in the middle of the diagram there is a water shut-off switch. Where on the car is this switch located? TIA, Mike

The switch itself? Usually right smack on the thermostat housing.

[mfendley]

I thought the switch on the thermostat housing was to change vacuum sources to the vacuum advance on the distributor. The diagram above makes it look like the switch is inside the passenger compartment (there is a black line that shows the dash panel) and maybe a push/pull piece (similiar to the override for the headlights)

The switch operates the hot water cut-off valve. Follow the white plastic vacuum line coming through the firewall to the switch (low on the right side of the engine). The plastic vacuum line becomes brittle over the years and may have been replaced, at least in sections with a black rubber line.

Rick

Originally posted by mfendley
I thought the switch on the thermostat housing was to change vacuum sources to the vacuum advance on the distributor. The diagram above makes it look like the switch is inside the passenger compartment (there is a black line that shows the dash panel) and maybe a push/pull piece (similiar to the override for the headlights)

Wow, you're right.. it does look like there's a push/pull switch similar to the headlight override switch. Weird. I would think it'd be near the A/C controls but you never know...

The "Water Shut off Switch" is located on the top of the air distrubition box accessable from BEHIND the glovebox. Just remove the 6 screws holding the glove box in and you'll see the switch sitting on top of the big black air box. You'll notice that the swicth is activated by the "Cold/Warm" slider button from your A/C control on the console. If the cable is not adjusted properly when fully over in the "Cold" position you'll notice the actuator will not compress the button on the switch. If the switch doesn't get activated then the valve allows HOT water from your water pump to enter the heat exchanger and you'll never get your A/C to blow cold air. A quick way to check to see if your switch is working properly is warm up your engine and follow the heater hose coming FROM your water pump to the "Water Shut off Valve" the hose should be warm/hot BEFORE the valve but room temp after the valve, i.e. NO hot water is getting past the valve. As a side note, my problem with this whole deal was the screw holding the "Cold/Warm" cable going from the console to the "Water shut off switch" was broken off at the control assembly. If you take your right side kick panel off you'll notice the cable coming off the control assembly and it has to make a sharp turn towards the front of the car and this puts a lot of pressure on the small plactic piece holding the cable to the controller, if this breaks you're screwed and you'll never get the switch activated.

[Bob Chadwick]

I have some pictures of where it is on my web site under Controlling the Air Temperature.

[pws69]

Originally posted by 21again
The "Water Shut off Switch" is located on the top of the air distrubition box accessable from BEHIND the glovebox. Just remove the 6 screws holding the glove box in and you'll see the switch sitting on top of the big black air box. You'll notice that the swicth is activated by the "Cold/Warm" slider button from your A/C control on the console. If the cable is not adjusted properly when fully over in the "Cold" position you'll notice the actuator will not compress the button on the switch. If the switch doesn't get activated then the valve allows HOT water from your water pump to enter the heat exchanger and you'll never get your A/C to blow cold air. A quick way to check to see if your switch is working properly is warm up your engine and follow the heater hose coming FROM your water pump to the "Water Shut off Valve" the hose should be warm/hot BEFORE the valve but room temp after the valve, i.e. NO hot water is getting past the valve. As a side note, my problem with this whole deal was the screw holding the "Cold/Warm" cable going from the console to the "Water shut off switch" was broken off at the control assembly. If you take your right side kick panel off you'll notice the cable coming off the control assembly and it has to make a sharp turn towards the front of the car and this puts a lot of pressure on the small plactic piece holding the cable to the controller, if this breaks you're screwed and you'll never get the switch activated.

Great detail. Thanks for another entry in my "Corvette Tips and Secret Tweaks" manual!