CCU use Monovalve to control temp

[chomamma]

Simple question. Assuming the temp sensors send appropriate signals to CCU. How does the CCU control Temperature? Does it turn on and of the monovalve?

[R Leo]

Originally Posted by chomamma

Simple question. Assuming the temp sensors send appropriate signals to CCU. How does the CCU control Temperature? Does it turn on and of the monovalve?

You got it. No power to the monovalve opens it and allows coolant to circulate through the heater core in heating mode.

[tangofox007]

Originally Posted by R Leo

No power to the monovalve opens it and allows coolant to circulate through the heater core in heating mode.

If there is no power to the monovalve, you are going to be in the "heating mode" whether you want to be or not!!!

[James L]

And the aux water recirculation pump factors into this also (for flow/water pressure to the monovalve).

[sailor15015]

The way I've heard it explained here before is that it cycles the valve open and closed depending on how hot you're telling the CCU to make it. More heat equals a longer open cycle.

[chomamma]

If the valve is closed. Does the aux wp still pump?

[SGT John]

if the valve is closed, then the aux water pump shouldn't be able to push any hot coolant into the heat exchanger in your cabin.

Originally Posted by SGT John

if the valve is closed, then the aux water pump shouldn't be able to push any hot coolant into the heat exchanger in your cabin.

True, but there is one clarification; the monovalve and the aux pump are in the return line from the heater core, not the supply.

[James L]

Chasing an a/c problem on my 1993 W124, when the a/c is running, the metal return line comming out of the firewall to the aux water pump under the washer tank is hot, the top metal cap of the monovalve is hot also. the a/c expansion valve to the evaporator line is cold but the line from the evaporator to the expansion valve is warm, the a/c suction line to the compressor is warm also.

Do you think I have a monovalve/aux pump situation? keep getting a 30 flash fault code (recirculation pump). I am getting the correct voltages to the monovalve and aux pump.

[sailor15015]

Originally Posted by chomamma

If the valve is closed. Does the aux wp still pump?

Anyone? I'm guessing not because it seems like it would burn the pump out or create some crazy vacuum if the aux pump was pumping against a closed monovalve.

[chomamma]

OK let me try to get this straight. The imput side of the heater core is attached directly to the engine block or water pump. The coolant comes from the engine into the heater core unmolested. Exiting the heater core on the drivers side is the AUX water pump. Basically sucking water from the heater core. It pushes into the monovalve and if open circulates hot water through the system.

Please correct me if I am wrong.

Two questions:

1. Is the Aux water pump always working or does it cycle?
2. What circuit tells it to come on or off?

MY monovalve lines are cool when a/c is on, but my aux lines out the fire wall are hot.