Heater Blows Cold - Unusual Problem

Because it's best to have the flow order be:

hot water from engine -to- heater box (radiator) -to- valve -to- main radiator

That way the hottest water reaches the heater box first and the average temperature of the water going thru the valve is lower.

They did very cleverly design the valve so that the pressure from the water pump helps hold it in the closed position -- so that minimizes the current needed to hold it closed (although that does add some solenoid heating when the heater is off as you noted). The difficulty with a valve designed to be closed with no current is that the current required to open it is much larger -- since the heater is usually off, they made the design trade-off to have a little current flowing more often so that they didn't need to have a larger current flowing when the heater is on. One other minor side benefit is that when you drain the coolant, the valve is open so no need to do something to open it

 

No, when the valve is closed, there is no water flow so the (stationary) water in the heater core stays cold (even when water circulating in the engine and main radiators is warm). The thermal resistance to the heat moving up the long column of stationary water in the hose going to the heater core is huge (so virtually no heat makes it into the water inside the heater core).

 

Ferrari Mondial - Heater Hose RHD part # 61150000



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It cannot be changed without disassembling the HVAC unit, as it connects to the bottom of the heater core, which is deep inside the housing, which catches the AC condensation water.
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Hot water exits the engine, runs through the lh sill and enters the top of the heater core via the brass fitting.
Exits heater core at the bottom and enters the electromagnetic valve at the top via the molded rubber hose.
Exits the valve via the bottom connected to another molded rubber hose and passes through the fire wall.
The bottom unconnected one here:
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It connects on the outside to the return pipe of the rad via the small inlet:

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So, the valve is after the heater core and the heater water isn't fed back into the radiator before returning to the engine.
You can see the heater valve exit hose connecting to the rad return pipe here right before it enters the centre tunnel:
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You're welcome!

 

Holy Cow. These photos are far better than any service manual for showing parts and positions!

 

The Automotive Artistry of Unseen Parts.

... would make a beautiful “coffee table” book. SG


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