We have verified with testing the way the thermal timer works.

The internal switch works like an old school turn signal flasher relay where a pair of bimetal strips makes and breaks contact as the bimetal strips cycles between cool and hot due to the heat generated while current is being applied.

When cold, the internal switch/contact inside the thermal timer passes a ground supplied by the housing of the thermal timer and it's connection to the engine block to the terminal labeled "W" on the thermal timer.

When enough current passes through the thermal timer during a cold start or when the engine is warm, the switch/contact moves and actually makes contact to the power supplied to the thermal timer via the starter motor so both contacts now get power. So if you test both contacts at the CSV, both with have positive voltage when you use the starter when the contact move to the warm position.

I have never understood why the ground switches to power and not just to an open position.

I hope I am misreading your suggestion to ground the thermal timer directly to trigger the CSV. If you ground the "W" terminal on the thermal timer that supplies the ground to trigger the CSV, you will be creating a potential short because as I stated above, both terminals will get power when it switches to the warm position. FYI, when the thermal timers fail they almost always failsafe with the internal switch contact in the warm condition so power gets supplied to both thermal timer terminals and the CSV WON'T open.

If you want to test the wiring for the CSV, then unplug the wire connected to the "W" terminal on the thermal timer and then ground just the wire and that will activate the CSV.
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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com