'92-96 HVAC Vacuum System
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Others '80-91 similar, except '87-early '88 which use a cable for Floor/Def/Panel. The '80-86 vacuum reservoir is a plastic ball on the R wheelwell.
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This is the most common failure of this vacuum system:
It can be permanently remedied by replacing the underhood vacuum lines with silicone:
The next-most-common problem is objects (especially pens) falling into the defrost register and binding the doors. Remove the heater core for access.
'87-93 trucks are known to have problems with the reservoir on the evaporator cover warping the cover until it cracks, or the sonic weld attaching them cracks; particularly if the shiny insulation is missing, exposing the reservoir to exhaust manifold heat.
A problem for '87-91s is the temperature cable coming out of its adjusting clip:
'92-94 trucks with a single push-pull temperature cable should be upgraded to the revised pull-pull (looped, apparently double) cable & control panel.
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The vacuum check valve at the top is
Motorcraft YG-193-C 
![hvacvac.jpg '92-96 HVAC Vacuum System
[url=https://www.supermotors.net/registry/media/894687][img]https://www.supermotors.net/getfile/894687/thumbnail/vaclinesefi.jpg[/img][/url] . [url=https://www.supermotors.net/registry/media/894692][img]https://www.supermotors.net/getfile/894692/thumbnail/cruiseservoearly.jpg[/img][/url] . [url=https://www.supermotors.net/registry/media/512260][img]https://www.supermotors.net/getfile/512260/thumbnail/accontrols9296.jpg[/img][/url] . [url=https://www.supermotors.net/registry/media/724438][img]https://www.supermotors.net/getfile/724438/thumbnail/tsb951110accables.jpg[/img][/url] . [url=https://www.supermotors.net/registry/media/665548][img]https://www.supermotors.net/getfile/665548/thumbnail/tsb961307hvaccable.jpg[/img][/url] . [url=https://www.supermotors.net/registry/media/265819][img]https://www.supermotors.net/getfile/265819/thumbnail/tempblendcable.jpg[/img][/url] . [url=https://www.supermotors.net/registry/media/498379][img]https://www.supermotors.net/getfile/498379/thumbnail/dash9296.jpg[/img][/url] . [url=https://www.supermotors.net/registry/media/883864][img]https://www.supermotors.net/getfile/883864/thumbnail/acboxin.jpg[/img][/url] . [url=https://www.supermotors.net/registry/media/883867][img]https://www.supermotors.net/getfile/883867/thumbnail/acboxout.jpg[/img][/url]
Others '80-91 similar, except '87-early '88 which use a cable for Floor/Def/Panel. The '80-86 vacuum reservoir is a plastic ball on the R wheelwell.
[url=https://www.supermotors.net/registry/media/741005][img]https://www.supermotors.net/getfile/741005/thumbnail/hvacvaclines.jpg[/img][/url] . [url=https://www.supermotors.net/registry/media/148977][img]https://www.supermotors.net/getfile/148977/thumbnail/5.8l-right.jpg[/img][/url]
This is the most common failure of this vacuum system:
[url=https://www.supermotors.net/registry/media/767412][img]https://www.supermotors.net/getfile/767412/thumbnail/recircline.jpg[/img][/url]
It can be permanently remedied by replacing the underhood vacuum lines with silicone:
[url=https://www.supermotors.net/registry/media/1090170][img]https://www.supermotors.net/getfile/1090170/thumbnail/siliconevac.jpg[/img][/url]
The next-most-common problem is objects (especially pens) falling into the defrost register and binding the doors. Remove the heater core for access.
[url=https://www.supermotors.net/registry/media/958838][img]https://www.supermotors.net/getfile/958838/thumbnail/coredrain.jpg[/img][/url]
'87-93 trucks are known to have problems with the reservoir on the evaporator cover warping the cover until it cracks, or the sonic weld attaching them cracks; particularly if the shiny insulation is missing, exposing the reservoir to exhaust manifold heat.
[url=https://www.supermotors.net/registry/media/964781][img]https://www.supermotors.net/getfile/964781/thumbnail/evapins.jpg[/img][/url]
A problem for '87-91s is the temperature cable coming out of its adjusting clip:
[url=https://www.supermotors.net/registry/media/901664][img]https://www.supermotors.net/getfile/901664/thumbnail/blendcable87.jpg[/img][/url]
'92-94 trucks with a single push-pull temperature cable should be upgraded to the revised pull-pull (looped, apparently double) cable & control panel.
[url=https://www.supermotors.net/registry/media/551112][img]https://www.supermotors.net/getfile/551112/thumbnail/cableshvacdual9296.jpg[/img][/url] . [url=https://www.supermotors.net/registry/media/665548][img]https://www.supermotors.net/getfile/665548/thumbnail/tsb961307hvaccable.jpg[/img][/url]
The vacuum check valve at the top is [url=https://www.amazon.com/dp/B0065US9RU/]Motorcraft YG-193-C[/url]](https://www.supermotors.net/getfile/1166439/fullsize/hvacvac.jpg)