I built the monovalve replacement heater control I found here for those hard to find monovalves that are now out of stock and not being made anymore!

Hmm interesting. I have like 3 spare monovalves though.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Which monovalves? It looks like the one you have made has a vacuum port? Im confused.

__________________
Current Stable:
1994 S500 v140, 210k miles, white with grey.

Former Mercedes in the Stable:
1983 300CD Turbo diesel 515k mi sold (rumor has it, that it has 750k miles on it now)
1984 300CD Turbo Diesel 150 k mi sold
1982 300D Turbo Diesel 225 sold
1987 300D Turbo Diesel 255k mi sold
1988 300 CE AMG Hammer 15k mi sold
1986 "300E" Amg Hammer 88k mi sold (it was really a 200, not even an E (124.020)
1992 500E 156k mi sold
etc.

He made a replacement valve setup that uses an electric solenoid to control vacuum to a vacuum powered valve. Rather than the electromagnetic mono valve from MB.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Too bad you are in Phoenix.

I'd really like to know how that system runs when it's 10°F. outside. It's a very clean install and gets rid of the pesky monovalve forever.

Good job.

BTW, I changed the title of your thread so that others can find it in the future.

Thanks! I never thought about changing the title to be relevant to the topic! guess that would help though huh?

My original endorsement of this thing would tell me it works fine even in 10F weather!

At a high heat setting, all available vacuum is directed to the resevoir and none to the vacumm operated valve leaving it fully open.

When the setting is turned to cold, the vacumm is directed completely to the valve fully which closes it.

My one wish is that the solenoid were a bit more sensitive to voltage changes so it would taper the available vacuum so I didn't have to fiddle with the temp control so much, but if your worried about no heat or an insifficient amount of the stuff, NO PROBLEM HERE!

I'd like to hear from anyone who knows of a more sensitive solenoid I might try out to regulate vacuum with.
Monovalves for the 123 are no longer being made and this was an alternative to th $330.00 price tag of the ONE I found in Indiana!

This whole setup was about $50.00

One word of advice though, I tried it without the auxillary water pump and with it and it seems to function better with it. If you need maximum heat, leave the aux pump in place!!

I have like 4 monovalves hanging in my garage.. just the housings.. I'm hoarding those things.. just like the climate control resistor ..

I wish I could have found one, but not even at auto dismantlers yards were any available! I'll keep looking, but I'm not hopefull!

The climat control resistor is one of the easiest parts to make for yourself!
It's a bit of a bulky thing, but you can find ceramic wire wound resistors in the 300 to 500 watt range fairly easily! Just wire them up to the appropriate terminals and go. I did have to craft a mount for them out of a piece of Lucite and fasten that to the fender wall though!

It's not frankenstein, it's fronkinsteen!

The solenoid is a switch.........it's not designed to provide regulated vacuum to the valve.

So, the question that remains, unfortunately, is whether the original valve is regulated by variable voltage. If it is, then the new setup is not really acceptable in terms of regulation of cabin temperature.

If the original valve is regulated like a switch, then the new setup should provide perfect cabin temperature regulation.

The fact that it cannot do this is definitely a problem.

the buyers on ebay don't know that

Well now i was told that the Monovalve IS regulated by variable voltage and your saying this isn't the case or your not sure?

I could go outside and fire up the car and run the climate control to the terminals normally connected to the monovalve and find out with a sensitive voltmeter! If this is not the case, then I haven't found the right vacuum bleed setting yet and that is another thing to try!

i'm sure they don't! It's handy to be an engineer at times! If you had to, the worst case scenario is making your own air wound resistor with a Constantin and Tin wire cut to the appropriate length! Because Constantin and Tin is going to react to voltage changes and switches like a spring, I would put a Capacitor of at least 5 MF and 150 volts across terminals 1 and 4 to soften the voltage slam though. It would be better for the blower motor!

OK, Here's what I just found out.
1. In the defrost mode, temperature control in fully on heat no matter where the thumbwheel is. On dual, floor and vent, the thumbwheel works but it's working erratically because the monovalve has a 10.5 Ohm resistance in the coil and the vacumm switch I installed is 26 Ohms, so a 15 ohm resistor 10 watts power dissipation is recommended. The full vent position has the same characteristics.

2. The monovalve does NOT operate on varying voltage, it simply cycles on and off letting short bursts of coolant flow through the heater core depending on where the temp thumbwheel is set. Warmer temp requirements would open the monovalve more often, cooler temp settings open it less often, but it is either fully open or fully closed! There is no in between!

3. The vacuum controlled heater coolant flow valve reacts pretty fast to switch changes between on and off, so some sort of a auxillary resevior for vacuum is going to be installed in the line just for temp control.

4. A bleed off rate of about 25 to 30 % of available vacumm made a world of difference in avoiding those rapid temp changes, especially while driving!

My schematic will be amended to reflect these changes and I'll post the new changes here for those who do not have 2 or 4 monovalves hanging up in the garage! A vacuum resevoir bottle from any Chrysler should work and this brings back memories of putting a resevoir in the feed to the Auto Temp system in the New Yorker and Imperial models helped avoid these rapid temp changes too!:

There's conflicting opinion on that topic. I was always of the assumption that the valve functioned like a switch.......either on or off.......depending on the CCU. However, Kerry has found the valve receiving voltage levels other than 12V.........so, we're not fully clear on the function.