Replacement monovalve heat control
 

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!:D

Hmm interesting. I have like 3 spare monovalves though. :D :D

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

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.

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.
:D 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!:eek: I'll keep looking, but I'm not hopefull!:(

The climat control resistor is one of the easiest parts to make for yourself! :D
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.:thumbsup: 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!:D

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!:confused:

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!:D

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.:thumbsup:

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.:thumbsup:

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!:thumbsup:

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!:P:P 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!::headshot: :D:D

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.

On our car's I have measured them all a cycling of 12V on and off. Thats probably why that rubber diaphragm doesn't last long, because its moving so often depending on your heat settings.

It does indeed work by cycling and letting bursts of hot water through the heater core. I think my valve is not closing all the way, because even with the car at 80C, I get only mediocre temp air when the blower is on above "low". I'm going to take it apart and clean/sand it soon. Mine was a used one though, so it may not be that great to begin with. Might just buy the new repair kit. Or, maybe my diaphragm tore already....

Well, mines a 1983, but it could be very possible that this is correct too. The thing to do here then would be to first check and see what kind of system you have.:)

With a 10.5 Ohm monovalve, it would function under both conditions and both would explain the need for an auxillary pump, the heater putting out any serious heat would be depleted without it and temps would be hard to regulate.:D

If there is a wide varying voltage changing at less than 3 volts at a time, I would be looking for a malfunction somewhere because any change in monovalve settings with less than 3 volts variation is going to have negligible effect on the 10 Ohm monovalve solenoid itself.;)
This would be a 4 step process, like Chrysler used to make these changes. 3 volts is necessary to move the solenoid any at 2.5 Ohms of resistance at/per 3 volts of power.

If this is the case, then just simply leave the resevoir off and the system should respond just fine to a air bleed of 30%.:thumbsup:

The rubber in these monovalves is so thin, I'm not suprised it doesn't wear out sooner!:eek:

This is one of the reasons I thought I could try and design something better or just as good but with better reliability that isn't already outdated.;)

I put in the additional vacuum resevoir and it works much better now! Temperature changes are much more slow and gradient and i'm pleased with these results!

Brian Carlton, I don't think you would be at all displeased with these results, even in upstate New York.

The voltage to the mono valve is very close to constant. The on off pulse time varies with temp requirements. In the mono valve there is a diaphragm between the valve body and the valve. There is a very small water bypass hole with a fine screen to keep it clean and open. Also a fine spring to appose the valve opening motion.
The valve will be more open with a longer voltage pulse and closer to a closed valve with a shorter power pulse. The valve will float in a given position based on pulse length from the control. if the diaphragm is torn or removed the valve will open and close at the pulse timing but still regulate the heat. The water pulse can be felt by holding the incoming hose. and heard with the engine off. I have run this way for a few years.
If the valve is not operational remove the valve and clean the screen and bleed orifus.

Could someone post a picture of where this setup is mounted? The heat in my 83 300SD is fine, but my friend's 85 300SD has intermittent heat. Maybe this is his problem. Thanks.

John :confused:

Its right next to the battery behind the false bulkhead. Easy to spot. Has four flat head screws on top and a little cord plugged into it.

Why do you need the vacuum reservoir...........if the valve is functioning as a switch??

Yes, at least it is in mine! It is either on or off and with the size of the vacuum heater control valve, the resevoir allows the vacuum to slowly rise and fall which gives an easier transisition with the flow of heat!:cool:

When you turn the heat on high however, it cooks and with AC going full blast keeps the car clear of fog too. It happens to be humid and raining in Phoenix today and tomorrow and after I went into the city today it appears to be working fine. The one thing to get used to is that the temp wheel works but you have to wait a little longer for results.:D

I'm not grasping why you want to slow the operation of the valve? Wouldn't it be preferable to have the valve act instantly.........upon demand from the CCU.........in similar manner to the monovalve?

It appears that the temperature regulation is not the best. The monovalve, when it works properly, will maintain temperature in the cabin very accurately.........+/- 1 degree, typically.

Regulation is ok, but with the resevoir the heat doesn't go rapidly from hot to cold and back to hot. I can set the temp where I want and get pretty consistent warm air with the ac pump running!

With the resevoir holding some vacuum and a 30% bleed off the valve opens and closes slowly and ui don't have to feel the rapid temp change out of the vents or floor.:thumbsup:

I understand what you're doing with it........but, I can't reconcile it with the function of the monovalve. If the monovalve functions like a switch.........on or off.........the new system should perform in similar manner.

If it doesn't, then the monovalve function is not exactly what we think it is.

True! the monovalve has a taper in it so even when it is open, it's not as wide open as the valve I'm using now. ;)

The monovalve also has a set of springs to dampen the movement and the vacuum valve does not, it reacts fast.

The resevoir permits the valve to open and close a little more slowly to my taste and monitor the heat setting better! Without the resevoir, the valve just opens and closes rapidly and this bugged me!:D

The monovalve reacts instantly, as far as I am aware. However, it might not allow the same flow rate as your current valve. It appears that the flow is too great for most operating conditions. The use of the reservoir should dampen the system sufficiently. Be interesting to see how well it holds cabin temperature.............

True, the monovalve was not as wide open as this is. It's almost like not having a valve in there at all!:eek:

As far as cabin temps go, it seemed fin on my way into Phoenix!:)

I had the up/down button pushed and it stayed slightly warm just like I wanted not going from hot to cold.:thumbsup:
The resevoir seems to dampen the movement of the valve allowing it to slowly open and close!:thumbsup:

Please report back on your results during the winter. I'm most curious about the ability to maintain temperature...........as compared to the monovalve.

Will do, but this is Phoenix Arizona!:sun1:
Winter means we put on long pants to wear with out golf shirts!:D

If it gets down to 40F it would only be at night!;)

Tomorrow I am removing and inspecting my monovalve, as I am sick of freezing to death in the car. Its getting rediculous, I can drive 25 mins, car is at 75-80C and my cabin temp is about 25-30F. Very little heat. :mad:

It is currently 12F outside. So I reeeeally need to fix this. If I can't get the monovalve to work, I will fashion a copper tube for direct 100% flow. :eek: Maybe THEN it will be warm!

Yeah I know what you mean! I used to live in a cold climate and I often miss it, but not if i'm without car heat!:D

Our 300D has MEGA heat.....and it comes on in about 2-3 mins full force. It will heat the whole cabin of the car up in maybe 4 mins to a so-warm-its-uncomfortable temp. That is my goal tomorrow in fixing my system....

Could you post some pics for the DIY? Thanks.

John :rolleyes:

According to weather reports, Grand Rapids has a snowstorm going on! Hope you get that heater fixed!:D

Brian I am in Flagstaff,AZ now, its 34 d F right now. Maybe I could try it.

Austin, you put that system in as well..........??

Its not quite here yet, I am going out in a few mins to grab the monovalve....:D I will try to take a few pics of what I'm doing with my phone, but remember, its COLD, I will be working fast! :eek:

Good luck! It looks like that snowstorm is coming to you by the end of today!

Well, I took it out and cleaned it up/inspected it....didn't fix anything. I think my issue is low-flow or something. The hose going in to the heater core is HOT with the engine at temp, and the ones coming out are only slightly warm. Maybe its plugged up? Is this a possibility? Anyways, I took some pics of what I did.

First I removed the valve plunger, then I disassembled it on the table, I also opened up a valve I got from the U-pick last week, in the pic you can see the diaphragm on that one is torn. :rolleyes: I just cleaned it up and put it all back in, didn't make any difference...it still does cold when on cold....and "warmish" when on hot. I doubt the problem is the valve....its probably the aux water pump or core itself. Although even going 60mph its lukewarm....so its probably the core. :o

Here are all the pics in order:

http://www.tglmarketinginc.com/mbfor...lve/valve1.jpg


http://www.tglmarketinginc.com/mbfor...lve/valve2.jpg


http://www.tglmarketinginc.com/mbfor...lve/valve3.jpg


http://www.tglmarketinginc.com/mbfor...lve/valve4.jpg


http://www.tglmarketinginc.com/mbfor...lve/valve5.jpg


http://www.tglmarketinginc.com/mbfor...lve/valve6.jpg


http://www.tglmarketinginc.com/mbfor...lve/valve7.jpg


http://www.tglmarketinginc.com/mbfor...lve/valve8.jpg

and the rest of the pics....assembly is the reverse of removal, so I didn't take any pics of that....

http://www.tglmarketinginc.com/mbfor...lve/valve9.jpg

http://www.tglmarketinginc.com/mbfor...ve/valve10.jpg

http://www.tglmarketinginc.com/mbfor...ve/valve11.jpg

http://www.tglmarketinginc.com/mbfor...ve/valve12.jpg

http://www.tglmarketinginc.com/mbfor...ve/valve13.jpg

http://www.tglmarketinginc.com/mbfor...ve/valve14.jpg

thanks for the pics. Have you tested your auxillary pump?

John

The aux pump is a super pain to get to since its buried under all those hoses behind the bulkhead, but I may give it a try if replacing the engine thermostat doesn't help anything. (I only get to 65-75C most of the time, and it takes a while) I know it has been ailing a long time and probably died, it used to make bad sounds when I was starting the car in the morning, and now it is silent. I have a replacement in my spare parts in excellent/almost new condition that I can put in, but that will be an afternoon project....maybe next weekend I will look into it, if replacing my thermostat Wednesday doesn't help. It probably is the aux pump....:rolleyes: However, I have it fused at the plug (that red wire thing in the pics) and it hasn't blown the fuse :confused: So I have no clue....if it was dead you would think it'd blow the fuse. Its only a 1A quick-blow fuse.

Your Auxillary pump is buried back there? Mine is on the fender well underneath the air filter where it can be easily reached. I've never seen a Aux pump placed there before. Did you relocate it for some reason?

He's got a W-126. Relocation courtesy of Mercedes-Benz.:mad:

Do yourself a huge favor and remove the battery and the removable section of the forward firewall. Makes the job 1/10 as difficult.;)

Oh! I thought he was working on a 300 D!:headshot:

yeah, I wish it was in the same place as on a 300D....oh well.

I will at least remove the battery, not sure if I want to un-do the false bukhead though, I'll decide when I am actually working on it, but I will probably unbolt and move it over a little.

I still don't get why it did not blow my 1A fuse I put in there. Kinda odd. It needs to be replaced either way, as it made bad sounds for a long time....