Help W123 300D Monovalve issue
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300D
Help W123 300D Monovalve issue
My mono valve went bad so I replaced it today. The new one keeps thumping or pulsing. Wouldn't that mean that this mono valve rebuild kit was defective ? Also my A/C compresser wants to run even when heat is on full. Can someone help. I have heat when idling only. If I take the relay on the fender for A/C out the compressor goes off. I am wondering if all this is because the A/C compressor won't go off?
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From: In the Shadow of the Tetons
2013 ML350 Bluetec
I have found that the new monovalve cartridges are built in such a way that the spring can't hold the valve open against the flow of coolant. They literally blow shut. You're seeing heat only at idle because the flow of coolant is slow enough to not push the valve closed, but at higher RPM's the coolant is fast enough to draw the valve closed. The new cartridges need a stronger spring to hold them open.
Having tried several new cartridges from a couple of different sources, and having removed the valve assembly from the car and tested it with the variable flow from a garden hose, I can confidently state this is what is happening. I have since replaced the electronic valve with a manual ball valve (3/4" and related plumbing adapters) and can control the flow of coolant through the heater core manually. A PITA to be sure, but when I want heat I get it (160 degrees from the vents)) and when I want cool, I get that by closing the ball valve.
I've since given the car to my nephew along with some basic instruction in what I've done with the valve. Gonna let him mess with it now.
Having tried several new cartridges from a couple of different sources, and having removed the valve assembly from the car and tested it with the variable flow from a garden hose, I can confidently state this is what is happening. I have since replaced the electronic valve with a manual ball valve (3/4" and related plumbing adapters) and can control the flow of coolant through the heater core manually. A PITA to be sure, but when I want heat I get it (160 degrees from the vents)) and when I want cool, I get that by closing the ball valve.
I've since given the car to my nephew along with some basic instruction in what I've done with the valve. Gonna let him mess with it now.
