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I have an 86 900S and the cabin vents suddenly only blow cold air.
Searches on this site quickly suggested the heater control valve. I have just finished experimenting with the valve and have some results I can't explain.
First, I have plenty of coolant and the cabin fan, temperature guage, and engine cooling fan all work correctly. No coolant is dripping in the cabin. The heater control rod is connected to the heater valve.
Now, after the car warms to operating temperature:
* On the engine side of the firewall, both the incoming and outgoing
coolant hoses (to the heater core) are hot. Good.
* The same is true for the (brass) hoses on the cabin side of the
firewall up to the heater valve. Good.
The heater valve has three connections:
* I: An input (hot coolant from the engine)
* O-heat: An output to send this hot coolant to the heater core
* O-noheat: An output that connects to the return from the
heater core (let's call it R) and permits short-circuiting
the heater-core
Here's what has me confused. No matter the setting of the heater control (on or off), 'O-heat' is always hot, but 'R' is always cool. However, just a little before when 'R' intersects with 'O-noheat', it becomes hot.
It would seem to me that this information suggests the heater valve is bad: 'O-heat' should be cool when the heater control is off. But this would suggest the valve is broken in the heat-always-on position: If 'O-heat' is hot, why is there no heat?
Of course, the control valve itself (brass) is always hot. Perhaps it is hot enough to heat the 'O-heat' pipe even when no coolant flows through. If this is true, maybe the problem is that the heater valve _does_ work but the heater core is plugged. However, many people have said that heater cores rarely go bad.
Maybe both the heater valve and core are bad!
Many thanks for any insight. My wife gets cold. :)
posted by 24.238.217...
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