We have 2 Lennox roof top heat pump units in our office building. They
are a T-Class unit and a CHP-Class unit,
http://www.lennoxcommercial.com/prod...?category_id=1.

We like to clean or replace the air filters since it has been over a
year since they were installed.

Does anyone have experience with these 2 models of HVAC and know how to
gain access to the filters?

Thanks

The smart thing to do is pay for a service call by the company that
installed it. Lacking that, find a local guy who works with roof top
equipment.

Then just watch him. You may decide that "next time" you will again watch
him rather than DIY.