Caterpillar D400 Air Conditioning Parts. We offer many choices to keep you cool and comfortable in your Caterpillar. If you don't see your Air Conditioning parts or components in this category, contact us here as we have additional AC parts for the D400 outside of this website. You can also use the searchbar above for more universal fitting AC parts. In addition to compressors, clutches, and evaporators we can help with fittings, blower motors, receiver driers, adapters, condensers and more.