HVAC goes to floor/defrost while accelerating/cruising on Expressway

[DerekTheGreat]

Update:
Ya dudes were all right about the TBL, Motorcrap replacement was leaking. System itself held 22 -whatever abbreviation used for vacuum- for 3 minutes. Back started to hurt so I had to move, otherwise I would've tested it longer. Tested it right at lines going to TBL, the black line. Was going to test soup can and system from soup can's line but couldn't get line off. I think it's safe to say that trash isn't trash since it is all linked together and held vacuum. On a side note, I couldn't find vacuum distribution tree either, hidden by lots of garbage or I'm just not good at finding things. Well, I did discover my throttlebody is leaking coolant at the gasket so that's gotta get refurbed..

You dudes aren't going to like the solution though- I cobbled another TBL together from the old body with the new TBL's guts, that one seemed to hold vacuum whereas the "new" one didn't.

[His Royal Ghostliness]

Eh, I'm all for simplifying things, but if more complicated suits your own needs better it's all good - I myself am adding 4-wheel ABS where people tend to remove even the simple rear-only, so yeah, if this TBL works and holds up run it.

[jaywish]

Cool.

The tree is not obvious. It lives near the PCV. If your symptom goes away don't play any more with the lines as you might make a leak. The lines are old after all. I actually am impressed that they hold up as well as they do given even newest box is at least a "classic".

[DerekTheGreat]

Eh, I'm all for simplifying things, but if more complicated suits your own needs better it's all good - I myself am adding 4-wheel ABS where people tend to remove even the simple rear-only, so yeah, if this TBL works and holds up run it.

Meh, I'm just stubborn. Stupid car had it from factory and so I'm trying to keep it that way since I don't feel like yanking the upper intake to get to vacuum lines and shiz. If this one leaks what I'll do is just seal up the holes on the inside of the TBL.
Also, What goes south on those is that thermostatic piston/plunger job it seems. New one is much more sensitive, also explains why my factory one didn't work well despite me reconditioning- Once I popped it open I could see the metal slider barely made contact with the other pin, plus there's lots of wear on those parts so that isn't helping.

It's worth noting that the aftermarket (Motorcraft) TBL has nipples that are considerably narrower than the factory TBL, could be what accounts for some of the leak problem and why I decided to use the factory body with 90% of the replacement's parts. Other thing I noticed is the little slider that opens & closes the vacuum path between the two nipples is a bit shorter than the factory one, probably also what accounts for some of the leak, so that part I didn't reuse. I reused the factory o-ring as the Motorcraft one looked damaged already, LoL, timebomb waiting to happen I suppose. Good thing I didn't start road tripping with that...

Cool.

The tree is not obvious. It lives near the PCV. If your symptom goes away don't play any more with the lines as you might make a leak. The lines are old after all. I actually am impressed that they hold up as well as they do given even newest box is at least a "classic".

Oh, great. No wonder I didn't see it lol. I hope not to touch the lines any more and hope they live for many more years haha.