Vents not blowing like they're suppose too

[Ludius_Maximis]

I've got an interesting one here. So, when I first got it the vents didn't blow all too well. Air was still flowing through the defrost and the passenger vents, but barely out the sides and the bottom. Recently, while I was jumping a friend who left his lights on his old F150, I placed my negative post on the hood latch in front. It sparked a little. The next day I noticed that the vents were blowing a lot more air. Like a lot more air. The side vents had real air flow coming through them, and the front vents where blowing as hard as I've ever felt them. But when I turned off the engine, I could hear something like air hissing behind the dash near the center. It'd hiss for about 30secs before it stopped. Now my side and passenger vents are back to barely having any air flow, and the hissing sound isn't there any more. Anyone have any ideas what it might be so I can point my mechanic in the right direction, or if it's something I might be able to do myself?

'92 XLT 4-door Sport Manual Trans.

 

[Dora 1993]

You use the word flowing to describe how the airflow was before. And now, after the jumpstart ordeal you use the word blowing. To me it sounds like the blower motor wasn’t working, then it was, now it isn’t again. the blower motor is very easy to check, and very easy to replace.

 

[Ludius_Maximis]

You use the word flowing to describe how the airflow was before. And now, after the jumpstart ordeal you use the word blowing. To me it sounds like the blower motor wasn’t working, then it was, now it isn’t again. the blower motor is very easy to check, and very easy to replace.

By blowing and air flow, I mainly mean just blowing. Thanks, I talked with an old timer and he pretty much said the same thing.

 

[Ludius_Maximis]

I'm kinda hesitate to say it's the blower motor. Because there was no noticeable difference I could hear in the blower when it was working correctly. Can the blower motor be the cause of the hissing noise I heard after turning the engine off?

One other thing too, the hissing I heard, I tried to see if I could hear it from the engine so I popped the hood. I couldn't. It's only from the inside and it sounds like it's coming either directly behind the radio or beneath it.

 

[Dora 1993]

Do the hvac levers on the dash feel like they are still connected and moving stuff?

 

[Ludius_Maximis]

Do the hvac levers on the dash feel like they are still connected and moving stuff?

Yes, it does still seem like they're working. Cause I am able to change the airflow from defrost to front passenger to floor.