HVAC vac. line ?

[Mr.Diesel]

Up by the RH hood hinge there is a little vacuum servo thingy on my F350 that is missing a line. Any ideas where it should go?

 

[icanfixall]

That line feeds from the wireing harness just below it. Somehow its supplied from the vacuum pump but on mt rig its all wraped up in the harness.... Kinda a dumb way for it to be routed...

 

[international]

On my 92 it was rotted off. I had to hack into the wiring harness and use a connector and new piece of line to reconnect to the black elbow on the servo.

 

[jim x 3]

Mr. D: The lines and routing for climate control vacuum are different for different model years. For my '88 the vacuum line to that actuator does NOT come directly from the vacuum pump but instead from the fresh air/recirculate lever switch on the dash. That actuator (near RH hood hinge) is in fresh air position w/o vacuum and recirculate with vacuum applied. Vacuum from the pump is supplied to the other side of that vacuum switch. Both vacuum lines route thru the ductwork and RH side under glove box, then to center of dash.
Regards,

 

[Dsl_Dog_Treat]

Up by the RH hood hinge there is a little vacuum servo thingy on my F350 that is missing a line. Any ideas where it should go?

Have no fear. I'll take care of it for ya since I have you truck.

 

[LCAM-01XA]

Jim, that particular line never gets vacuum from the pump directly, its the routing is always like you said from the vacuum switch on the dash. The difference is actually the switch itself, if I understand you correct your '88 has a separate switch for that door, whereas '89-up trucks have the switch built in with the vent-selector lever, as in it automatically closes the door when you choose "off" or "max A/C", and keeps the door open in all other lever positions. In my '90 truck I wired in a separate vacuum solenoid and installed a stand-alone switch for it so I can open and close the air door manually as I see fit, kinda like how you can with your factory setup

 

[nyteshades]

The 88 and the 89 are the same.

 

[LCAM-01XA]

So then it was in '90 that the control panel was changed? Your '89 as a separate switch for the fresh air door, like the '88 does?

 

[Agnem]

And for the record, the 87 had yet another AC panel. Seems they had a hard time deciding what to do in the late 80's.

 

[nyteshades]

So then it was in '90 that the control panel was changed? Your '89 as a separate switch for the fresh air door, like the '88 does?

On the control panel, inside the cab, no I don't have a separate switch for the fresh air door. I do have a vacuum controlled switch/actuator against the firewall under the passenger side hood hinge that controls the fresh air door.

My 88 xlt , both 89's (custom and xl), and my Dad's old 90 xlt didn't have a switch inside on the control panel either but they all had/have the vacuum switch (not 100% sure on the 90 having the vacuum switch). Come to think of it, my 93 xl didn't have an inside switch either. I can't remember if the door was controlled via an electric or vaccum switch.

 

[LCAM-01XA]

On the control panel, inside the cab, no I don't have a separate switch for the fresh air door. I do have a vacuum controlled switch/actuator against the firewall under the passenger side hood hinge that controls the fresh air door.

My 88 xlt , both 89's (custom and xl), and my Dad's old 90 xlt didn't have a switch inside on the control panel either but they all had/have the vacuum switch (not 100% sure on the 90 having the vacuum switch). Come to think of it, my 93 xl didn't have an inside switch either. I can't remember if the door was controlled via an electric or vaccum switch.

Oh, I see, what you call a vacuum switch is actually a vacuum servo, and it's there on every single '80-'96 truck with factory A/C, no exceptions. The real vacuum switch (as in the thing that switches vacuum to the different vacuum servos moving the different air doors) is behind the control panel on the dash.

And like Mel said '87 trucks use different control panel than the rest of the bricknoses, altho I've seen some '88s with that panel too - the main difference between those and the '89-'91 is the separate control of the fresh air door, the '87-'88 have that while on the '89-'91 the operation of the fresh air door servo is integrated withing the main vacuum switch behind the control panel on the dash. What I was going after with my add-on solenoid was the manual control the '87-'88 trucks have, basically I feed the factory servo full vacuum from the tree on the firewall and use the solenoid to interrupt that vacuum as I wish to open and close the air door, the factory vacuum line that used to feed the servo is capped as it's no longer used.

 

[nyteshades]

Ah I see. That's an interesting idea.

 

[LCAM-01XA]

Honestly if I knew at the time that the '87-'88 trucks had that feature from the factory I'd have just swapped in a control panel from one of those, instead of messing with the solenoid and the wiring for it, but oh well it works good so no reasons for me to redo it the factory way.

 

[Dsl_Dog_Treat]

Well no worries Ty, I found a light tan vacuum line coming out of the harness that the rubber grommet had rotted off. Pulled one out of my parts stash and all is good.

 

[Mr.Diesel]