High ambient fans should be installed when running a chiller in a high ambient environment. This is typically an environment over 95°F (35°C). These fans can run at double the motor speed, from 1250RPM to 2500RPM. There are fan speed controllers to overcome any issues with low ambient temperatures, such as at night for example.
The noise created by the high ambient fan speed can be mitigated with the addition of a fan speed controller pack. This option is not available for K9 and K12 chillers as they have high fan speed as standard. A high ambient variant of the K9 is available.