Can someone tell me what the vacuum motor just above the blower motor under the hood does? I noticed that the vacuum line going to it is completely broken off, but all of my A/C & climate control functions seem to work okay, with the exception of occasional max A/C problems. I have a 93 F-150 5.0 E4OD. Thanks for any input.

 

That's for the fresh air blend door. It closes (vacuum applied) in only the "off" and "max a/c" positions. There should be a white vacuum line going to it. What kind of max a/c problems are you experiencing?

 

Thanks for the reply, brown 4x4. My problem with max A/C is that I can run it for a few minutes, then the air starts blowing out of the defrost ducts. If I turn it off or switch to normal A/C, I can switch immediately back to max & it works for a few more minutes before going back to defrost. I was told this could be a small vacuum leak, which made sense to me. It would run until it lost vacuum, & then go to defrost. But with the line completely broken, shouldn't it always be on defrost while in the max A/C position? I don't have much knowledge on the climate control system, so any & all input is appreciated.

 

The only vacuum difference between max and normal a/c is the addition of vacuum being applied to the fresh air blend door motor in the max a/c position. I agree with your vacuum leak theory, since defrost is the position it goes to with no vacuum applied to any of the vacuum motors. I’d try fixing your broken line and see if it solves your problem.