Mono Valve Voltages - Page 2 - PeachParts Mercedes-Benz Forum

hispassion · #16 08-27-2007, 09:26 PM

Richard,

Will this work on a 1990 W124 Gasser? Also, can the coolant move in a reverse direction when at high rpm (say above 3K)?

I may eliminate my heater valve and go with this set-up if it'll work on mine.

Please advise.

Thanks kindly,
Michael B.

Richard Wooldridge · #17 08-27-2007, 11:35 PM

Hi Michael,
I don't know just what the setup on the 124 is, but if it's like the 380/560SLs or the 123s it should work fine. I don't know the answer to your water flow question, maybe someone familiar with the 124's will chime in...
One thing I really like about this setup is that when the car and weather is cold/cool, say 40 degrees, the heater will go full blast until the cabin gets up to the correct temperature, but then will immediately modulate down to the correct temperature to maintain whatever the setting is. When the weather is hot, the AC comes on immediately, no rush of hot air out of the climate control system. I think this must mean that the default position of the new heater valve is the closed/cool position, instead of the open/hot position, as the monovalve is - with the original configuration, the climate control always put out hot air for a few minutes after starting on a hot day.

#18 08-27-2007, 11:39 PM

Quote:

Originally Posted by Richard Wooldridge

- with the original configuration, the climate control always put out hot air for a few minutes after starting on a hot day.

My 300D did that (for a few seconds, not minutes) until I replaced the monovalve, now it works perfectly.

hispassion · #19 08-28-2007, 01:08 AM

Thanks Richard!

The default position on the Heater Valve (or monovalve) is open on a 124, so it would seem on a hot restart, that the heater core would be heat soaked and have difficulty with initial cool down. I'm not sure why MB designed the valve to close with power on.

I'm no engineer, but I did stay at a Holiday Inn Express and I would have designed it differently.

I've been chasing a nagging problem for a few days now and it seems I (with the help of others on this board) may have found the problem.

When you have a moment, take a look at this thread... 300E - Warm air from vents and 3k rpm.
I mentioned your mod in one of my posts over there!

Thanks again,
Michael B.

mplafleur · #20 06-09-2009, 12:18 PM

Quote:

Originally Posted by Richard Wooldridge

Hi Brian,
... in all positions except economy and off the AC compressor is engaged continuously, and the heat is controlled by adding heat to the AC.

Is the compressor really engaged ALL the time, or does it cycle?

Cr from Texas · #21 08-27-2009, 01:34 AM

Richard and Brian,
I got referred to this thread and hope you are still monitoring this one or will catch it when I bump it to page 1.

I like this fix and was convinced it was the way to go instead of a new monovalve (I actually have a new complete assembly). But I've got a couple of questions.
1. If the no voltage default for the original valve is open and the no voltage (no vacuum) for this one is closed, won't the automatic temperature mode modulate in the wrong direction? Applying voltage to lower the temperature with the original valve; would't that raise the temperature with this setup?
2. I wasn't aware my car (83 300D) even had this auxilary water pump. What was it's purpose? Brian, you removed yours - is there a downside to doing that? Other threads certainly indicate a downside of this pump failing and frying the CCU (I certainly don't want that.

This thread and fix is a couple of years old. Have many of you made this modification?

Brian Carlton · #22 08-27-2009, 09:04 AM

Quote:

Originally Posted by Cr from Texas

2. I wasn't aware my car (83 300D) even had this auxilary water pump. What was it's purpose? Brian, you removed yours - is there a downside to doing that? Other threads certainly indicate a downside of this pump failing and frying the CCU (I certainly don't want that.

This thread and fix is a couple of years old. Have many of you made this modification?

The pump is present to get coolant into the heater core. Without the pump, the flow is relatively slow and the heat is slow to come up. Below 20°F., the heat is insufficient. I've bought a brand new pump and will be installing it before the winter arrives. The SD is just too cold without it.

If the pump locks up and draws too much current, it will fry the board in the CCU. The installation of a 1 amp fuse in series is recommended.

I have not made the above modification.

Jeremy5848 · #23 08-27-2009, 01:17 PM

Quote:

Originally Posted by hispassion

. . . The default position on the Heater Valve (or monovalve) is open on a 124, so it would seem on a hot restart, that the heater core would be heat soaked and have difficulty with initial cool down. I'm not sure why MB designed the valve to close with power on. . . .

There is a check valve built into the monovalve to prevent hot coolant from circulating through the heater core when the engine is off.

As to mplafleur's question, yes, the compressor is 'on' all the time when the climate control system is working, unless you have the 'EC" button pressed. The rationale is that system response is faster and smoother if the heat exchanger is cold and you modulate the degree of cooling with the fan speed and the monovalve. It's also likely that the compressor runs more efficiently if it doesn't have to start and stop all of the time. The power drain from the engine in such a design is minimal, or so it is said. I cannot prove that by the numbers other than noting that I do not see a difference in fuel economy winter to summer that I can attribute to the load of the compressor. It is probably there, just covered up by other factors such as my right foot.

The monovalve failure alluded to by Brian (pump freezes, draws too much current, frys the PBU -- Push-Button Unit) happens in the 1982-85 W123 cars with ACC-III. They should have a 1 amp fuse added to either one of the pump's wire leads. If 1 amp burns out, try 1.5 amps.

The W124-series cars have a redesigned PBU that shuts down if an overload happens. The first design shut down the entire PBU, a later redesign shut down only the affected circuit. It is a "automatic circuit-breaker" type of protection -- when the fault is repaired, the system comes back to life all by itself.

People who live in warm climates have been known to remove the aux pump, replacing it with a piece of pipe. Those who live in or visit cold places should leave the pump in place.

Jeremy

Richard Wooldridge · #24 08-27-2009, 07:23 PM

I've been using my setup for several years now with no problems at all - as I see it, the main advantages are that it is a cheaper, more reliable setup than the monovalve, and also keeps the water from flowing when the vehicle is first started up, so the heater doesn't blow a blast of hot air before going to the AC mode.

Cr from Texas · #25 08-28-2009, 03:13 AM

Quote:

Originally Posted by Richard Wooldridge

I've been using my setup for several years now with no problems at all - as I see it, the main advantages are that it is a cheaper, more reliable setup than the monovalve, and also keeps the water from flowing when the vehicle is first started up, so the heater doesn't blow a blast of hot air before going to the AC mode.

Thanks for picking up on this old thread. There must also be a check valve in the vacuum valve since no voltage = no vacuum = open valve. Is the lack of a hot blast due to the delay to build vacuum? No, that doesn't fit if default is open valve?
Why would this system also replace the auxillary water pump? Looks like it would have the same flow rate as a monovalve without the auxillary and that seems to be insufficent in the winter?

Richard Wooldridge · #26 08-28-2009, 08:19 AM

The monovalve's default position is OPEN with no power. This valve's default position is CLOSED with no power. The vacuum solenoid is connected so that when the car is started and vacuum becomes present, then the valve's function becomes the same as the monovalve's. I left the aux water pump connected in my 380SL, so cannot comment on whether it would work well without it.

Cr from Texas · #27 08-28-2009, 02:37 PM

OK, Thanks.
I'm clear now and any backflow with power off is prevented by the default closed position so a check valve is not necessary.

My first step is to remove the bad monovalve and substitute a T with a hose connection to use to backflush the system.

micalk · #28 08-28-2009, 05:03 PM

Quote:

Originally Posted by Jeremy5848

The monovalve failure alluded to by Brian (pump freezes, draws too much current, frys the PBU -- Push-Button Unit) happens in the 1982-85 W123 cars with ACC-III. They should have a 1 amp fuse added to either one of the pump's wire leads. If 1 amp burns out, try 1.5 amps.

Would this apply to the W126 for those years as well? They have a different ACC unit p/n, but I believe this is really only to cover the control of an additional vacuum pod. The rest of the system is the same IIRC.

pselaphid · #29 08-28-2009, 07:11 PM

This may be a far fetched notion, but if the Napa valve fails, is it possible for the vacuum attachment to suck coolant leaking around the valve through the switch and ultimately into the vacuum pump and engine. Hopefully the internal arrangement of the valve will not allow this, but it would be nice if this bizarre way to lose an engine was impossible, and not just extremely unlikely.

Also, I'm sort of confused now about the default position of the valve. I'm pretty sure I blew through it to confirm that it was OPEN without vacuum (default position), and hooked it up according to that assumption. Anyway, mine works, whichever it is. Maybe someone that is buying one can test it and confirm one way or another.

Cr from Texas · #30 08-28-2009, 10:04 PM

Quote:

Originally Posted by pselaphid

This may be a far fetched notion, but if the Napa valve fails, is it possible for the vacuum attachment to suck coolant leaking around the valve through the switch and ultimately into the vacuum pump and engine. Hopefully the internal arrangement of the valve will not allow this, but it would be nice if this bizarre way to lose an engine was impossible, and not just extremely unlikely.

Also, I'm sort of confused now about the default position of the valve. I'm pretty sure I blew through it to confirm that it was OPEN without vacuum (default position), and hooked it up according to that assumption. Anyway, mine works, whichever it is. Maybe someone that is buying one can test it and confirm one way or another.

Good question. I was wondering why MB opted for an electrically controlled valve when most of the valves on a 123 are vacuum controlled. Maybe this is why.

The same concern would apply to a gasser except then the coolant would be drawn into the intake manifold rather than the crankcase.