2003 Honda Odyssey No air flow

We have had this "fixed" twice, and neither fix worked. We do no have heat or ac. Most people want to charge my ac, but will that give me heat? Very little flow come out of any temp, but the temp is usually outside air temp. I had thought it was that little door that wasn't switching. I thought it was the fan motor because I can get the motor sound to change but not much air ever come out. Just took a long drive and never had air to defrost more than 2 inches of windshield. My husband is convinced the heater core is clogged. Any way to check this? Sounds like a long risky process. Thank you! I would be happy to send pictures of anything.