Apologies in advance for possibly using incorrect terms for things, I'm new.

I removed the single knob control on my shower stall because I was not getting cold water and thought I needed to replace the cartridge. As far as I can tell the cartridge is functioning properly. However this is what is behind it, and where I believe the problem lies:

[s1350.photobucket.com]

The house is 70's era. Have you ever seen such a contraption, and if so, what is it called? Google images has failed me. It is permanently welded to the supply pipes.

Hot water should (and does) come out of the hole on the left. Cold water should come out of the hole on the right, but it doesn't. I assume it is clogged as we have a lot of sediment in our water. If that is the case, how do I clear it? The hole on the bottom returns the water to the shower head above and is clear (hot water goes through).

There is a tub on the opposite side of the wall that shares the supply lines and I get hot and cold water through that faucet. However all of those tub fixtures are a few feet below the shower knob on the opposite side so I think there is a crossover in there.

If you want to see more pictures, you can flip through the photobucket album.

Thank you for any help you can give!

If you want to take a stab at this yourself, I would recommend using some plastic and duct tape to seal up the hole in the wall. If you haven't already, shut the house water off, shut the hot water tank supply off, and open the cold side of a lavatory faucet in the same room as your shower. With a flashlight and a pipe cleaner handy, see if you can feed the pipe cleaner into the right hand hole down the waterway. While you are at the tub, have someone turn the water supply on slightly so that the sink next to the shower runs at about half flow. This will give you a small amount of pressure so that dislodged material can hopefully flow out, but not so much that the debris acts as a plug. If you can get the pipe cleaner in the line and water starts moving, shut the sink off so that the flow is directed into the shower valve. Keep moving the pipe cleaner around and then pull it out with the water flowing and hopefully the debris comes out with it. I would have someone then turn on the water supply full blast for about 3 full seconds, then shut it down so that everything can be reassembled. Just a thought, but a pipe cleaner in a cordless drill chuck might work too.
Another possibility is using a rubber tipped air sprayer attachment with an air compressor might be able to blast debris loose, but without a trickle of water flowing, it could end up somewhere else, like the shower on the other side.

Thank you for taking the time to reply. I was able to thread a stiff wire into the pipe (I don't have a pipe cleaning brush or a small enough snake) and make the 90 degree turn into the waterway, soon after which I meet resistance. This is worrisome because that pipe is much wider at that point. I wish I had a little camera to see what the heck is causing such a complete blockage. Otherwise I am going to have to cut into the wall from the other side to get a better look. (Perhaps the pipe makes another turn there?) If I can't dislodge the blockage I guess the pipe will have to be cut and replaced.

Still wondering if anyone has seen such a valve. It is a standing joke with this house that whenever we call in professional help the guy is guaranteed to say, "Well, I've never seen THAT before!"

The only experience I had like that besides a J.L. Mott was a house that someone that used parts from a mobile home to plumb the entire thing.

Interesting. The house, while never a mobile home, was originally a vacation/2nd home that may have been built by the owner. Probably out of scraps by the looks of it. The second owner did a lot of DIY as well. We've spent the last 15 years fixing weird things, for sure.

One thing you can be sure of is that NO ONE even made a single valve, therefore there are thousands of them somewhere, you just need to find someone who HAS worked on that valve previously, which can be difficult given the hundreds of possible sites you would have to access.

I kind of like the design, as most of it is outside the wall and easy to work on and understand...except when the obstruction is further back like this appears to be.

I'm just hoping for no surprises in the wall in light of the nearby tub and its incestuous relationship with the fixture in the shower stall. I use the tub all the time to wash my dog (hence the handheld shower low on the wall) but virtually never use the shower. I'm praying everything is piped correctly and demo will be minimal if needed. When I get it all repaired I have to remember to run the water once a week to keep things flowing.

I think a chunk of debris from down the line is more likely. I would bet that this happened after you shut the main off to do work elsewhere in the house.

I can't see in the shadow but is there I balancing spool in the notch at about 5 o clock?

I don't think so. We are getting a lot of dirt out of the cold water line by using a test tube brush I borrowed from work but just can't dislodge the big clot. If we inject water in with a syringe it runs back out, dirty. I'm going to keep trying all weekend and next week if it's still blocked maybe a plumber has a tool better suited for the job?

Well, I have a CO2 tank with about 2,000 psi in it that might blow it out.