even though your e34 may not have one, it may have just been omitted. the slot to squeeze in a M/F, could exist. It can be a PITA just to check it out, but even if there is NOT a slot, you might be able to clean out the area in front of the evaporator.

Use a vacuum cleaner with long snout and various size brushes to loosen trapped dirt and leaves. As another posted previously, cleaning could improve airflow.