How to change air filter on a Trane XE1000

Trane XE1000 is an outside split system heat pump unit, it's does not have an air filter. It is installed with an air handler, the indoor part of the system that moves the air through the evaporating coil and the furnace. They are most often packaged and sold/installed together but the air handler still has its own part number, something like TWE060A-B or TWE060P13 etc. Check the part number on the unit inside, it will be more relevant to your question. The installer could have done the air filter in a couple of different ways. Look for a box that can house a 20"x20" filter, 1" thick - a typical size for this air handler. The filter box can be either just before the return opening on the air handler or on a special return register, usually on the ceiling. Depending on the design on the filter box, you may have to either slide the filter into a 1-1/4" to 1-1/2"slot or fix it in place by a removable grill (typical for ceiling locations)    Anyhow, the Trane spec calls for a 1" thick low velocity filter and that's what you have to look for on the air return path. Once you know where the filter box is, take the old one out and get a replacement just like that.