The knob on the dash may be connected only to a blower for he defroster vents.
The levers on either side oof the emergency brake are attached to cables which run through the center tunnel and attached to airflow valves on the heater boxes on either side of the engine. They open and close those valves and allow heated air into the passenger compartment. It is the force of the engine cooling fan that forces air over the heat exchangers in the heater boxes…and then into the passenger compartment.
It is possible your TD has a supplemental heater. But it’s not likely.
Track the wiring from your dash switch. It may lead to a blower under the dash. If you do have a supplemental heater, it will lead to that device.
And take a look at the heat exchangers on either side of the engine. If they are hooked up, you will see a cable attached to a lever on each. And there will be some sort of duct work from the front of the heat exchangers into the passenger compartment.
Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
2005 Intermeccanica Roadster
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