Unlike the S14, the S15 has a replaceable air conditioner/ventilation filter. Judging by the state of the old filters which have come out of others cars, I'd say that they are very rarely changed. There is one simple way to tell almost for certain if this is this case. It will be evident as you read on.
Tools required: cross-head screwdriver and Stanley knife.
Parts required: FILTER KIT - AIR CONDITIONER - 27277-86F25
Service Interval: wash every 7500 miles/12000 Km or every 12 months (sooner in extreme conditions). Replace if noticeably dirty.
You need to first remove the glovebox. To do this, remove the two plastic pins located just under the base of the glovebox (Figure 1).
The pins are easy to locate and are shown in Figure 2.
With the pins removed, the glovebox can be opened and the door lifted free. A black metal plate will now be visible (Figure 3). This is where you can tell if the filter has ever been changed by Nissan. If you have a piece of trim running across where the two dotted lines are in Figure 3, it is unlikely the filter has been changed. The reason why is that this piece of plastic needs cutting to enable access to the filter. Ignore the two bits of cabling shown in Figure 3, as these are accessory cables.
With the cross-section removed, unscrew the five screw around the edge of the black plate (Figure 4).
The metal plate can now be lifted away. You will see that a connector is attached to it (Figure 5). There is no need to remove this connector. Simply let the plate hang loose.
You can now see the ventiilation system and a flap running down the left side of it (Figure 6). Undo the connector arrowed (1), then remove the clip arrowed (2). The cabling directly in front of the flap can now be tucked under the ventilation unit out of the way.
Remove the flap as shown in Figure 7. You will now see the filter.
Pull the filter out towards you (Figure 8) and marvel at how disgustingly filthy it is!
Figure 9 shows the comparison between old and new.
It is possible to simply wash the filter rather than replace it if you wish. Wash it thoroughly in warm soapy water and allow to completely dry.
Insert the new/cleaned filter, replace the flap and re-clip it into place.
Reattach the connector (Figure 6).
Reattach the black metal plate (Figure 4).
Place the glovebox door in place and reinsert its plastic pins.
Enjoy the fresh air!