Hello,
Does the coolant flow through the heater core at all time
or only when the cabin heater is on? Is it the same
for all Mercedes?
A

it flows only when you have it set to provide heat, providing it is working properly.

this would be true for basically all water cooled vehicles.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

once the coolant was warmed up enough to open the monovalve

__________________
-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon

If coolant is flowing through the heater core, the heat is on. Whether you want it to be or not!!!

And at what temperature does the monovalve open?

Great replies.
Thanks

The monovalve is controlled by the ACC controller if you have ACC.

Default is +12V and no ground to the monovalve so default is full coolant flow through the heater core. I'm not sure if this is the case in max heat mode. It is the case in defrost mode.

The ACC controller sends a ground signal to the monovalve to stop the flow of coolant. This is the case in max cool mode and off mode, if off is a mode, with the engine running. In other modes the controller pulses the ground signal to control heater core temperature.

I'm pretty sure the philosophy holds in MBs with dual zone climate control.

I'm don't know if MBs with manual AC have electric or mechanical valves.

Sixto
93 300SD 3.0

I have no clue. Judging by when my heat kicks on, I'd say around 50-60 degrees Celsius. I'm sure there's an actual number written down somewhere.

__________________
-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon

The question isn't just at what temperature does the monovalve close, it's depends on the temperature difference between the cabin sensor and the ACC setpoint.

Sixto
93 300SD 3.0

Oh yeah, I forgot about all that fancy stuff

__________________
-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon

He's playing with you simply because the monovalve is always open, provided that the cabin temperature is below the setpoint. Once the two temps get close, the monovalve begins to cycle to reduce the coolant flow and maintain the cabin at the setpoint.

Oh, my interpretation of the monovalve was that it opened to allow coolant to the heater core when the time was appropriate (don't let coolant through if the coolant isn't warm or when the temp inside the car is higher than the desired temp). That's why I said that original comment.

Thanks Brian.

__________________
-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon

When the coolant is too cold, the blower won't function, but the coolant will still flow to the core. When the cabin temp is above the setpoint, you're correct, the valve closes. But, it's not time dependent.

Interesting. Seems counterintuitive if you're trying to get the car warmed up ASAP to get that heater working. Probably doesn't make a huge difference though I suppose, maybe a few seconds longer than if the heater core was closed off.

__________________
-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon

so is there a difference to how, when and why the coolant flows through the heater core if its a car with no monovalve, and instead the acc servo. i bypassed my servo yesterday to get full heat, because the body of it had a crack in it and i was getting no heat in the car.

__________________
1980 300D