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heater valve in cooling system?


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getting ready to swap my thermostat tomorrow and reviewing Bentley. COOLING SYSTEM 19-5 at the top for Cooling system, draining filling and bleeding states:

With ignition ON, turn heater fully ON to open heater valve

This has me perplexed. Many cars do in fact have heater "valves" but the best I can tell from the schematic on 19-2 there is no heater "valve" in the system. Flow of the heater/cool in the system is mixed by the Temperature Mixing Flap to regulate the flow.

I see nothing in the Porsche Shop Tech Manual nor Bentley that says anything about a heater valve nor how it fits into the system.

  • Can someone explain to me if and where there is a heater valve on the 986 or if this is a misprint?
  • If there is in fact a heater valve is it electronically controlled somehow? (again there is no mention of it in the Porsche Service Manual).
  • If there is in fact a heater valve could it be closed manual (or opened) in a way to allow flow in the heater core and thus solve my lack of heat problem that is NOT caused by a heater mix servo issue or possibly NOT the thermostat?

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In AllData I don't see a heater valve either. I see a "heat exchanger" which seems to be what they call the heater core. It looks like the heat is always "on" with the temperature mixer flap opening and closing the valves to allow either hot or cool air in.

That's the problem with mine. I have no heat when it's below freezing outside. If I run the car to normal operating temperature, I can pull over and re-start the car and the heat will work againl. The temperature mixing valve makes a grinding noise so it was easier for me to find the problem.

Hope you find it soon before it gets too cold.

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In AllData I don't see a heater valve either. I see a "heat exchanger" which seems to be what they call the heater core. It looks like the heat is always "on" with the temperature mixer flap opening and closing the valves to allow either hot or cool air in.

That's the problem with mine. I have no heat when it's below freezing outside. If I run the car to normal operating temperature, I can pull over and re-start the car and the heat will work againl. The temperature mixing valve makes a grinding noise so it was easier for me to find the problem.

Hope you find it soon before it gets too cold.

Thanks fo the confirmation. We are really crossing our fingers for the easy and obvious "stuck open" thermostat. I highly recommend the Durametric software for the price because the guys now have "real values" for all the ACC system. Thus you can check the Temperature Mixing Flap movement from 0-100 percent of travel to determine it's "issues". Sounds like yours is obvious w/o the software!

I just wanted to make sure there was in fact NOT a fluid based valve in the system, as I would then suspect that more then a "stuck open" thermostat.

Therefor Bentley is just plain wrong because you wouldn't need to start the car and turn the ACC to "high" for any reason. Moving the mixing flap from cold to hot would have no affect on the flow of the coolant for draining and thermostat replacment!

Lastly it can be confusing for a DIY or newbie considering that Porsche Tech Manual, PET and Bentley all call the Temperature Control Valve Flap Servo Gizmo something different in each reference. Toss ALLDATA into that and I'm sure there is a fourth therm!

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