What is this vac line?? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 03-14-2001, 07:53 AM
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What is this vac line??

I was just wondering what this vac line is for on my 89 YJ 4.2 . It comes of the intake manifold near the firewall and is tee'd. One leg of the tee goes to the other side of the block for the axle disconnect etc., but the other leg has what I think is a check valve and then goes thru the firewall just above the level of the manifold. the line is one of those plastic ones red in color. Just curious as to what it is for as I can't seem to find it on any diagram.

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Ed
89 yj 4.2 weber tf999

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post #2 of (permalink) Old 03-14-2001, 08:15 AM
 
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Re: What is this vac line??

Usually on YJs and XJs, the red vac line is the main supply to the transfer case switch for the front axle disconnect. From the switch, green is for 2wd , yellow is for 4wd and blue is a vent that terminates at a check valve.[img]/wwwthreads_images/icons/smile.gif[/img]

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post #3 of (permalink) Old 03-14-2001, 08:20 AM
 
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Re: What is this vac line??

I thought that the vac line you are talking about goes into the fire wall to the heater control mechanism?
big ed

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<font color=red>'88 YJ, 4" susp,3" body,35's,283 Chevy V8,TH350,4.11's,D30,D35c</font color=red>
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post #4 of (permalink) Old 03-14-2001, 08:52 AM
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Re: What is this vac line??

This vac line is definitely not for the transfer case, that one is on the other side of the motor. If its for the heater controls, what requires vacuum to work? I thought it was all done by the lever switches in the dash.

ed
89 yj 4.2 weber tf999

post #5 of (permalink) Old 03-14-2001, 02:08 PM
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Re: What is this vac line??

In most vehicles, the lever swiches are just valves, and there are some vacuum motors that run the various doors and actuators. It's been like that since the '50's.
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Josiah

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post #6 of (permalink) Old 03-14-2001, 10:14 PM
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Re: What is this vac line??

There is a vacuum operated door in the intake duct that controls air flow into the duct. The vacuum is switched by the air control lever on the heater control panel.

jerry
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post #7 of (permalink) Old 03-16-2001, 09:34 AM
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Re: What is this vac line??

On my 89 YJ, the vacuum line through the firewall connects to a switch that controls which fan turns on. When the switch is activated the AC fan works, when deactivated the fan for the heater/vent works.

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