Hvac failure

[Mattmobile1993]

Hello everyone,

So I have air coming through my defrost and floor vent, but not the dash vents.

I had no vacuum due to a severed line that I found and replaced. After I did that, I then had air going through my vents, but it sounded and felt hesitant and then stopped working altogether after having to sit for a week.

Today I switched the check valve. What else could be the culprit for not having air run through the vents? I revved to 2500 rpms, and nothing changed.

Thanks

 

[1997ThunderbirdLXV6]

The rpm has nothing to do with it. In fact, I think vacuum is highest at idle.

I would start with a visual inspection of easily accessible points. You can also disconnect the vacuum connector behind the glovebox door and see if you have vacuum there with the engine running.

The failure point could be anywhere though. Behind the right fender, there's a vacuum tank which could crack from old age.

And of course, the mode selector switch could fail. But I'd focus on inspecting the lines first.

 

[XR7-4.6]

It’s almost certainly a disconnected vacuum line to the defrost door, it will be the yellow line accessible from the driver side footwell, the vacuum servo is roughly behind the secondary junction box(the box with a bunch of wires but not fuses)

 

[Grog6]

Is there a vacuum bottle in all of them? Haven't had that side out yet. The residual pressure valves in the F/R brake lines are on the other side.

 

[XR7-4.6]

Is there a vacuum bottle in all of them? Haven't had that side out yet. The residual pressure valves in the F/R brake lines are on the other side.

Yes all MN12s have a vacuum ball, it’s in the passenger side wheelwell.

 

[Grog6]

Vac reservoirs help tame the idle on MAP sensor cars with cams. we don't have either. Ours would keep the blend doors from slamming at wot.