another no heat problem

[BiXLL]

On one of my 240s, I just aint getting much heat at all. I have installed a new thermostat, I am sure system is completly burped. My slide control is working, and I can hear the door flap close. I am thinking that maybe the the fins around the outside of the heater are clogged not allowing the air to pass through them, and instead making it go around . Can I get to the heater core to vacume/blow it out? Where is it located, and can this be done without tearing entire dash out? Any other suggestions?