I have no heat in my 92 Explorer - I’ve put in a new thermostat, water pump, hoses, and heater core - still no heat. Could it be a problem with the “sealing” material around the heater core itself allowing the air to flow around the core rather than through it to be warmed?
The trouble may be with the vent doors in the air box. The door that allows the heated air from the heater core to flow through the vents may not be opening.
It’s more likely to be the blend door, but the outcome is the same. The blend door is what directs incoming air through the heater core, the AC evaporator, or a combination of the two, depending on the desired temperature. If the blend door is not moving the air won’t go through the heater core.
I think the blend door on your Explorer is vacuum operated. Look for disconnected or leaking vacuum hoses or a faulty actuator.
I think the blend door is working . . . when I change the heater control from cold to hot, there is a change in the air coming out . . . it’s luke warm at best, but on “cold” the air coming out is not modified at all. I can’t hear any “sucking” sound like a broken or disconnected vacuum hose. The A/C works fine … wouldn’t a faulty blend door also cause some problems with the A/C?