You might have to remove a panel towards the bottom of the unit to access the coils.  I have a 48″ True Sand. Prep (2/3 length opening) and I cleaned mine from the bottom (as it’s elevated about 9″).  You’ll see louvered or perforated vents where the baby radiator looking thing is (coils).  Fan will be on the back side of it and its more than likely caked with gunk…as normally happens.  What particular model do you have?