Straight from the Bently manual, Low speed = coolant above 96.75C (206.2F) and High speed 102C (215.6 F) or A/C pressure switch closed (refrigerant pressure above 18 bar/232 psi).

I got the manual and that's why I'm questioning my low fans not kicking in at 97C.

Rick, what is your info source with 102C as low fan activation temp?

With my manual switch, I'm turning low fans on at 95-97C when I hit traffic. I barely use AC as I drive top down most of time and prefer no extra drag on engine, so went for a 3-way switch. I also replaced OEM ballasts (supposedly 0.5 ohm) with 0.3 ohm/ 50w wirewound resisters so my lo speed should be somewhat faster than stock.

When I turn on AC, fans kick in at low speed so the circuit seems just fine, but somehow my DME does not trigger low fans at 97C.

That was from a previous post on this forum a few years back, but it looks like that information is incorrect. I also saw the same temp's listed in a thread on RennTech.

Yes I have seen posts on various forums mentioning different temp. levels at which the low speed fan kicks in. I wonder if earlier 2.5 is different from later 2.7/ 3.2.

Does anybody have an official Porsche service manual to look it up?

Personally I do not feel good about 102C trigger point with my car, so I flip my manual toggle switch around 95C.