Vacuum Leak or Blend Door or Both

[ronyounger]

I've been searching hi and low for the systems I am having with my 98 Explorer (Eddie B) but unable to find the answer.

Issue:
I have very intermittent air blowing in the front vents, the rear vents blow air.
I have intermittent heat blowing; rare in the front vents and about 40/60 in the rear. I used to hear a thump when hitting a bump, stopping short or making right turns and then the cool air would stop switch to heat. The thumps happen rarely now.

Sometimes (rarely) I can trigger the heat (in winter now) by pushing the climate control from Max A/C to vent to floor, etc.

The defrost works, but not full force. I do feel heat at the bottom of the plenum when no heat is blow in the front or rear.

I checked the blend door below the glove (cut out a piece and open and closed the door, but there was not change in the air flow;either cool to hot or blowing in the front. I did not take off the Blend Door Motor/Actuator because I wanted to see if keeping the Blend Door open or closed made a different - didn't seem to.

I a bit lost when it comes to checking for vacuum leaks. I've been looking for a diagrammed walk-thru of the possible vacuum lines.

Thank you and still searching......

 

[Turdle]

Hopefully this thread will help you

http://www.explorerforum.com/forums/showthread.php?t=192842&highlight=defrost+duct

 

[ronyounger]

Thank you. I have read and re-read that excellent thread. All of the information is amazing and it helped me troubleshoot a few possibilities.

It would be helpful to know:
1) what is the thump-like (when turning or rolling over a speed bump) noise that changes the cool air to heat.
2) is there a vacuum line that is tied to the front vents only (since the rear vents blow strong)
3) as part of my troubleshooting today - the Heater Control Valve seemed to have lost its vacuum suction when I pulled the line a few times; now there is no suction.

Thanks again.