My heater has left me in the cold the past few weeks and I'm tired of it. On A/C the airflow is fine (not great) but I can feel it, now that I need it to blow heat, it has failed me. I can put my hand on the vents and it feels somewhat warm but there is no airflow at all.

I'm don't really know how the HVAC system works, I took a glance a Shoebox's site but I'm still lost. I don't see how a clogged heater core could reduce the airflow so I'm thinking it is another problem. The check valve by the firewall appears (visually) fine.

Basically I go from plenty of airflow on A/C to no airflow on heater. Any ideas?

Edit: This is on a 1995 Z28 by the way.

 

Shoebox has a diagram of the system. You will see that the temperature **** turns a cable, that moves the flapper door from AC to heat. Could be the cable is loose or broken. Additionally, where the air blows from is controlled by flapper doors that are vacuum powered. Often, the check valve breaks, or a vacuum line cracks.

http://shbox.com/1/hvac_vacuum.jpg

http://shbox.com/1/vac_check_valve.jpg

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