2007 Toyota Prius Owners Manual - Page 319

5. Install the filter and filter case in the reverse order of removal. When setting the filter to the filter case, ensure that the flat side of the filter is down and the ribbed side is up. 82p009b Position the filter case so that the "yUP" mark is pointing up and install it in the vehicle. INFORMATION The air filter should be installed properly in position. The use of air conditioning with the air filter removed may cause deteriorated dustproof performance and then affect air conditioning performance. 4. Remove the filter from the filter case and replace it with a new one. 302