A couple of days ago I replaced my heater core which was definitely bad cause it was leaking antifreeze. I put everything back together and now there is very low air flow except from the defrost. and can hear the blower motor working and can hear it changing speeds from low to high. thought it could be the blend door but when I switch from cold to hot I don't hear any clicking as if it was stuck. any ideas?

 

Supply info on your vehicle, year, model, etc.

You may have broken or loosened an vacuum line or the blend door may be broken. Just guessing.

 

None of those will cause "diminished" air flow, they will all cause misdirected or incorrect temperature airflow.

The only way that airflow can be diminished is that either the blower squirrel cage isn't rotating freely or either the intake or outlet air path is blocked or restricted.

 

He did indicate the defrost air flow was normal or that the air flow was diminished in all modes but defrost.

 

Ah, misread that, you're right.

Probably loss of vacuum to the control head, it defaults to defrost under that condition.

 

Check your vacuum lines from the engine to the control unit, especially behind the battery.