Asus P1-AH2 - Manual (Page 25)

2-9 ASUS Pundit P1-AH2
2. Attach one end of the retention bracket to the retention module base.
3. Align the other end of the retention bracket (near the retention
bracket lock) to the retention module base. A clicking sound denotes
that the retention bracket is in place.
Make sure that the fan and heatsink assembly perfectly fits the
retention mechanism module base, otherwise you cannot snap the
retention bracket in place.
4. Push down the retention bracket lock on the retention mechanism to
secure the heatsink and fan to the module base.
5. When the fan and heatsink assembly is in place, connect the CPU fan
cable to the connector on the motherboard labeled CPU_FAN.
Do not forget to connect the CPU fan connector! Hardware monitoring
errors can occur if you fail to plug this connector.