kenwood basic M2 fan?

I have a Basic M2 amp powering some cerwin vega VS 150s @4 ohms, I have had this amp for a few years and never had the fan come on....even when I jam out with them, but it don't really get hot...does it take a lot of heat to make it come on?...I use it in my home theater and for my 2 ch listening...anyone have one doing the same???

Mine comes on just as it starts to get warm. There is a sensor for it but it has been unavailable for years. I found 2 quite a few years ago for my units