126 mono valve aggravation
 

Glad someone on the site put a heads up about bad aftermarket mono valves. Finally got fed up and cut the bottom cone shaped seal off. Heater works fine now. Is there some way to buy/find a valve that actually works? I can't find a Bosch valve anywhere. Or is there a permanent fix other than what I did?

I've had a couple of 123's in lately with heating issues and came up on the bad monovalves. Tell me more about removing the bottom seal to make em work.

There is a tiny c clip that holds the bottom seal and mesh piece on the spring loaded plunger shaft. Pull that off and there'll be guaranteed MAX HEAT!!

Thanks, I will check it out tomorrow.

Still a work in progress. you can get max heat with the above but the mono valve won't function to regulate heat. I am going to modify the rubber seal. I will let folks know how it works.

The bottom cone shaped seal is the stopper that the solenoid acts on. Cutting it off allows constant flow, same as replacing the monovalve with a pipe.

Apparently there is something I'm still missing here. Am I correct that with no current the valve is open (max heat). Why doesn't this valve work? Does the valve get stuck in the hole or does the negative pressure created by water flow suck it shut? Trying to see how to fix this so the valve works correctly. Is this company a division of URO? It is hard enough figuring how to fix these cars when the parts work!

Something like that. The spring is too week to resist the flow.

Yes, no current, valve is held open (by spring tension)= max heat. If you had a leak in the large diameter diaphragm, corrosion that developed could cause the solenoid to hang. If you are rebuilding it, you have to take it to bits and clean it so the iron core plunger slides freely in the coil. There is also a float valve that could jam due to debris. If you shake the monovalve, you should hear it rattle. If you blow into the bottom port (with monovalve in orientation as mounted in car), you should hear the float rise up and flow stops.

I find it hard to believe a weak spring can stop flow due to water current. Until I inspect one that actually does that, I am not buying it. I suspect it is due to other causes.

Ya, I find it hard to believe that also. Wish I had not thrown the old on out. I could take a micrometer and check dimensions. I have replaced several of these with discontinued Bosch part and never had a problem. Wrote a nasty email to MTC but will probably receive the standard reply: No one had this problem but you or we make the finest quality parts and everybody loves them but you.:P

poking around on the internet I found a valve made by Vollig. Has anyone tried these?

After you go through all that and yo azz is still freezing then you'll be buying that.

I just went through my own mono valve saga and I am certain that
weak spring was the cause and removing the lower seal from the plunger shaft was a definite fix for the short term. New MTC valve kit restored normal operation and is working as it should so far.

Where would I find an MTC valve kit?

I mean one that works, have tried two already that don't.

That may be so. Thing is, there are so many reports of new MTC kits that do not work, that they have weak springs, they fit tight etc that I don't know what to believe. Did the spring in your MTC feel stronger than the old one? By how much?

The monovalve can be tested on the be bench. With no power, connect horizontal inlet port via hose to faucet. It should flow out the bottom outlet port with faucet on low. If you turn up the water pressure, it should continue to flow. If not, then it may be due to a weak spring. Did you/ can you run such a test? While water is flowing, applying power should stop flow.

If you run the faucet into the outlet port, the check valve should prevent flow out of the inlet port if working properly.