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About a year ago I was on this forum whining about the cheap POS Chinese water shutoff vacuum switch I installed on my '79. This is the one mounted on top of the heater box that supplies vacuum to close the shutoff valve in the heater hose when you select 'Cold' on the temperature selector on the console. Anyway I bought the good USA made part, which I installed tonight. It seems to work, except for the fact that the spring on the vacuum switch is so strong that when I select 'Cold', the spring pushes the selector lever back toward 'Hot'. Anyone else run into this problem? Is there some way to increase the friction in the cable so the selector stays where I put it? Some other solution?
Years ago I too had the same problem on my 77. The new valve spring was way to strong. I tried adjusting cable no luck. Using the original switch spring here is what I did to resolve the problem.
Years ago I too had the same problem on my 77. The new valve spring was way to strong. I tried adjusting cable no luck. Using the original switch spring here is what I did to resolve the problem.
FWIW - I believe there is an error in the design of the system using a normally open vacuum switch. The issue I see is that in the summer when you start the car cold it works fine, vacuum is pulled and the valve closes before any hot water is created and sent to the heater core. However, once the car is heated up and then turned off, the vacuum goes away and the valve opens and the heater core and all plumbing to it shoot up to full hot temp. The only way I have found to prevent this during the heat of summer is to install shut off valves in both lines to the heater core. Only an issue in the heat of summer when your feet get hot or when you want to run the AC.
I wonder why they don's use a normally closed valve and then only circulate the heater core when vacuum is supplied. Would eliminate most of this issue. Maybe they want to fluid to circulate to keep corrosion down.
Well i didnt have that problem but on my 79 i had heat coming in the car all the time,so i went over to lowes and bought a water shut off valve and installed it on the heater hose by the motor and that took care of the heat in my 79!
A solution to be proud of. Unfortunately I no longer have the original factory spring. I only have the spring off the cheap Chinese POS I am currently replacing and I'm not sure if its any better. My list of ideas includes crimping the cable housing to make it bind a little, installing a spring to counteract the pull of the spring on the valve much like a throttle return spring, or installing some sort of rubber or foam to bind the travel of the lever at the heater box. None of these really appeal to me. And while installing a shutoff valve in the heater hose would certainly work, I like things to work the way the factory intended. I don't want to have to play with things under the hood just to turn on the heat or air conditioning. I would like to find a more elegant solution.
I don't know what valve you purchased that is made in USA. The one that is sold by Willcox is indeed USA made, and the spring used is made to exact original factory strength. The import valves are almost twice the original factory spring strength, and will exhibit the problem you are having. If you indeed have the willcox valve, you have other issues, and I would surmise it would be in the actuating cable or hvac selector. See link below.
A solution to be proud of. Unfortunately I no longer have the original factory spring. I only have the spring off the cheap Chinese POS I am currently replacing and I'm not sure if its any better. My list of ideas includes crimping the cable housing to make it bind a little, installing a spring to counteract the pull of the spring on the valve much like a throttle return spring, or installing some sort of rubber or foam to bind the travel of the lever at the heater box. None of these really appeal to me. And while installing a shutoff valve in the heater hose would certainly work, I like things to work the way the factory intended. I don't want to have to play with things under the hood just to turn on the heat or air conditioning. I would like to find a more elegant solution.
Be careful with this fix. I too tried cutting the new POS spring back along with other ideas. It is easy to create too much tension (like the new spring is doing) and the plastic arm on the heat selector slider gizmo will break when trying to engage the vacuum switch. Ask me how I know If the spring isn't tight enough then the vacuum switch can leak - hear again ask me how I know. The frustrating thing is that when the spring is that stiff it will hold your plenum door open just a tad even though the vac switch has enough movement to allow a vac pull on the water switch. For what's it's worth that little plastic arm is replaceable for $10, the entire selector switch does not need to be replaced.
In the end I admire the effort to get it back operational with OEM design, and will give it another shot this year. I just gave up last summer and put the cut offs in to get it running comfortably again. Good luck, please post back when you get a good fix for this.
I don't know what valve you purchased that is made in USA. The one that is sold by Willcox is indeed USA made, and the spring used is made to exact original factory strength. The import valves are almost twice the original factory spring strength, and will exhibit the problem you are having. If you indeed have the willcox valve, you have other issues, and I would surmise it would be in the actuating cable or hvac selector. See link below.
I did in fact get the valve from Willcox. Its a much better piece than the Chinese part. Just need to deal with the stiff spring. I was really hoping there would be some way of adjusting the 'stiffness' of the actuation mechanism that I don't know about.
So I found a solution - sort of. I added an elastic band to the end of the cable and it adds just enough to overcome the excess spring tension. Works perfectly. Of course its not a long term solution. We all know what elastic bands look like after a year or so. I'm going to try to find a spring that does the same thing.
I did in fact get the valve from Willcox. Its a much better piece than the Chinese part. Just need to deal with the stiff spring. I was really hoping there would be some way of adjusting the 'stiffness' of the actuation mechanism that I don't know about.
I've never had this problem with the USA valves, have you adjusted the cable? There are instructions in the AIM on how to do this.
I've never had this problem with the USA valves, have you adjusted the cable? There are instructions in the AIM on how to do this.
Willcox
Yes but as far as I know the cable only adjusts for length, not for resistance. My whole mechanism moves so smoothly that the spring applies enough pressure that the selector won't stay at the COLD setting. The cable probably had a little more resistance to it when it was new, but after 40 years of use, its pretty worn in. An elastic band at the valve end of the cable.provides just enough resistance to keep the selector in the cold position. If I can find a spring that provides a similar pull, I think I'll have the problem solved. Unless of course you have a better solution.
01-22-2018, 10:24 PM
Water shutoff vacuum switch revisited
A solution to be proud of. Unfortunately I no longer have the original factory spring. I only have the spring off the cheap Chinese POS I am currently replacing and I'm not sure if its any better. My list of ideas includes crimping the cable housing to make it bind a little, installing a spring to counteract the pull of the spring on the valve much like a throttle return spring, or installing some sort of rubber or foam to bind the travel of the lever at the heater box. None of these really appeal to me. And while installing a shutoff valve in the heater hose would certainly work, I like things to work the way the factory intended. I don't want to have to play with things under the hood just to turn on the heat or air conditioning. I would like to find a more elegant solution.
If the spring isn't tight enough then the vacuum switch can leak - hear again ask me how I know. The frustrating thing is that when the spring is that stiff it will hold your plenum door open just a tad even though the vac switch has enough movement to allow a vac pull on the water switch. For what's it's worth that little plastic arm is replaceable for $10, the entire selector switch does not need to be replaced.