The lower lever on my dashboard ventilation controls no longer regulates the temperature of the air that flows through the system. It's always hot. (The upper lever that directs the flow to "windshield/floor/off" works just fine.) Is there a diagram showing the linkage between the temp control lever at the driver's left hand and the heater control unit in the engine compartment? With thanks in advance!

You may need to replace your heater valve control cable or the heater valve.

New cables and heater valves are available.

If it's just the cable, you can fabricate 1 if you can find the sheath and solid wire and then bend the ends to make it fit.

FYI, I do have a new heater cable in stock and I might have the valve too.
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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com

Thank you for replying. I'll poke around under my dash to see if I can find any cable remnant and/or attachment point on the back end of the lever. On first examination I couldn't even find where a cable would have penetrated the firewall into the engine compartment. Should it be a pretty straight shot from A to B that I'm looking for?

Hello,

As long as the heater valve is the original style, the heater valve control cable doesn't go through the firewall.

The stock heater valve is mounted on the firewall , but the cable is connected to the back which is inside the car.

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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com

OK, thanks again. I appreciate your patience -- and foresee a larger flashlight in my future.

Dean;

I'd first establish if failure to control Heater Control Valve is a result of Bowden Cable issues, most common being sheath slipping (as shown here for Choke, but the action is similar: https://www.sw-em.com/checkchoke.htm#Reference_Information ), or a problem with HCV itself, see: https://www.sw-em.com/Heater_Control_Valve.htm

Good Hunting!