I work on instruments that have a Rapture motherboard with a Pentium III CPU. The heatsink and fan are always pre mounted. I had to replace the CPU fan mounted on the heat sink. When I removed it the air direction was blowing air on the heat sink not pulling heat away.
What is the correct air direction for the fan mounted on the heat sink?
More aboutairflow direction
Most of them blow downward on the heatsink fins. Never understood this, but that is what they do. Aftermarket styles have various configurations, usually some form of sideways.