Water Cock Valve Capillary Tube

[Captain Obvious]

What is the purpose of the capillary tube on the water **** valve for the heater system? The car in question is a 77 without air conditioning.

They reference the capillary on page BE-51 (Body Electrical) section of the 77 FSM. They talk about being careful not to damage it, but I cannot find any description of why it exists in the first place.

Some kind of attempt at feedback to stabilize the output air temp in the face of changing heater core temperatures?

[240260280z]

I am lost. Is the capillary tube the long cable-like part that connects to the door?

Edited June 18, 2012 by Blue

[Captain Obvious]

It's more of an "access panel" than a door. It's screwed into place and doesn't move once installed. They coil the capillary up and run it to a little access panel screwed to the heater box downstream of the heater core. In other words, the coiled portion of the capillary sits in the air stream after the air has gone through the heater core.

Best pic I could find is from http://www.zparts.com/zptech.html:

They are clearly sensing the temperature of the air after it has been heated, but the question is... Why? Are they adjusting the opening and closing of the valve with the pressure from the capillary?

And here's some pics of the water **** and it's associated capillary tube as installed from old threads:

http://www.classiczcars.com/forums/thread11152.html

http://www.classiczcars.com/forums/thread17858.html

http://www.classiczcars.com/forums/thread40835.html

[tlorber]

I don't own a 77 so I'm flying in the dark here, but are you sure it is a hollow cappilary? Normally when I've seen seen copper like that it has been in the context of temp control or sensing in refrigerators or A.C. units and they have been solid wire. I have one sitting at my shop from the beer fridge (that is now kaput) so I'll check when I get up there.

Since it is at the end, you may be able to resolder it.

Edited June 18, 2012 by tlorber

[240260280z]

"Some kind of attempt at feedback to stabilize the output air temp in the face of changing heater core temperatures?"

I agree with your guess.

[Captain Obvious]

I removed my water **** from my car and took a good look at the design. Based on that investigation, I'm going to change my guess a little...

I now theorize that it is an over-temperature prevention device. The reason I say that is because it appears that the device can only reduce the amount of water flowing through the valve, not increase it.

I'm guessing that it operates like the thermostat on the cooling system... The material inside the tube expands when it gets hot and pushes on a lever inside the valve which closes the valve. The hotter it gets, the more it presses down on the lever, and the more the valve closes.

All that said, I tried to test it by heating the capillary and valve with a hair dryer, and it didn't do anything at all. So, either I'm completely wrong, didn't get it hot enough to hit the threshold temp, or mine is simply broken.

Sure seems like an unnecessary piece of over-engineering...

[Captain Obvious]

are you sure it is a hollow cappilary?

I'm pretty sure it's hollow. I didn't cut it open, but there's a blob of solder at the end of the coil that resides inside the air box. I assume that solder is to seal the end.

It would be difficult to convince me that they could get any useful info through that thing if it was simply conduction through a solid wire. Not impossible, but difficult.

[240260280z]

It was probably filled with freon. I have seen similar but larger tubes for cooling transistors on audio amplifiers and on telecommunication circuit packs.

Most thermo-mechanical devices on cars use bimetal. Maybe the fluid filled tube was more convenient than bimetal for connecting the two distant parts.

[Captain Obvious]

I took the capillary device off the rest of the valve today and added heat again. Now that it doesn't have the pressure of the valve's spring pressing against the little plunger tip, the tip did extend a little when I heated the coil. However, it was compressible back with finger force. Also, when I was done, there was a tiny bit of some kind of liquid seeping out around the plunger tip. Not much... Only seen under magnification, but there was something coming out.

I stand by the theory that it's an upper-temp limiting device, and I believe it is supposed to be filled with some kind of liquid. I suspect some of my liquid has leaked out over the years and the resulting bubble is compressible which renders the device useless in application.

So nobody has ever seen any documentation as to the function and/or purpose of this thing? I'm the only one curious enough to look into it? Ever??

[Zed Head]

Oliver at zspecialties.com knows all about them. Rebuilds them too, but only if the tube is intact. He usually answers e-mails.

I think that you're right about its purpose as a control device. The idea is probably for BTU or calorie control, limiting flow as temperature (heat content) increases, so that you don't have to move the heat control lever as the engine heats up. The concept probably looked great on paper.

[240260280z]

Just searched the web:

Some heater control valves are "thermostatically controlled" with a capillary tube that extends into the heater air outlet. The capillary tube reacts to changes in the heater's output. This regulates the opening and closing of the control valve to maintain a more consistent level of heater performance.

Rebuilders:http://nyzcc.com/forums/cars-wanted/456

[Captain Obvious]

Just searched the web:

Haha!! I just read the exact same page not more than five minutes ago!!

Oliver at zspecialties.com knows all about them. Rebuilds them too, but only if the tube is intact.

Yeah, I found some info on people that rebuild the valves, and yes... Mine could sure use the help. But if I'm right about the function of the capillary, then I could live without it. At least unless I heat the core so hot that my air box bursts into flames! :eek:

I'm thinking that any mechanical valve that I can manage to stuff in there will work. I would really like to relocate the valve to the engine compartment so I don't ever have to mess that deep into the dashboard ever again. This whole thing started out trying to figure out why my air always blew hot regardless of the temp control lever. Now I've got the whole interior torn out and I don't know how the scope this project has managed to spiral so far out of control.