Hello all! thank you for reading first of all. Now, i have a 1997 4.2 L f150. Starting quite some time ago, the heater was failing to engage. we found that when we increased vacuum via popping the clutch or aggressive acceleration we would hear the blend door slam shut, and for air conditioning, we just drove more gently, so as not to increase vacuum. I've searched under hood for vacuum leaks, no such luck, but I am replacing the EGR vacuum solenoid tomorrow for it is inexpensive and whines after car is off, and have replaced climate control unit, and tested blend door motor. So before I go on a possibly wild goose chase of removing my dash, has anyone had this problem and fixed it, anything I am overlooking? or can anyone offer direction?
Thanks!