Vacuum line into the firewall?

[7900_Blazer]

My guess is this will be an easy question for you all.

On my 85’ K20, there is a very small diameter line the connects on one end into the larger vacuum line that runs into the vacuum reservoir, the other end runs into the firewall and under the dash somewhere.

What is this line for?

And for a bonus question, it being disconnected from the larger vacuum line, would that cause the engine not to run as smooth as it should at idle (vacuum leak)?

Thoughts?

 

[richard A lindner]

Ac and heater control

 

[WP29P4A]

It makes the doors in your heater box open and close to change where the air comes out, defogger vents, dash vents and under dash heater vents.

If the larger line is still connected to the carb/TBI or intake, and not connected to the smaller line, yes it will cause a vacuum leak.

 

[Craig 85]

Here's the diagrams you're looking for. In photo 2 disregard the upper left. It's for a fuel injected vehicle.

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[Grit dog]

It may run rough if you didn’t plug the port or tee that feeds it.