Brrr it's cold. I don't have heat. I have a '97 4Runner LTD 3.4 auto with the manual climate controls.

I checked to make sure I don't have any air pockets in the cooling system. I get hot pipes on both side of the core at the firewall.

With the blower fan running when I switch from cold to hot I get a noticeable reduction in air blowing out of the vents, regardless of which vent position is selected.

I know the blower works, I can hear it and air moves in cold. The A/C works like a champ. Coolant is full.

What can I check before I gut the dash to take the airbox out?

Also it was 4* when I drove to work this morning

 

Can you here the blend door change when you go from cold to hot?

 

There's also the coolant cut-off valve on the firewall, a cable from the HVAC controls is supposed to cut off coolant flow to the heater core when it's set cold enough - is that opening?

 

As far as I can tell the coolant valve is opening. The pipes get hot on both sides of the valve and both inlet/outlet through firewall.

The blend door sounds like it is clunking. I disconnected the cable on the actuator below the heater box and you can move it by hand with noise/flapping along with movement.

Does anyone have a flow diagram of the heater box? I'd like to try to rig/prop the doors open to force some heat until I can properly get this resolved.