Vacuum Line Mystery

[avid]

Hi everyone. I'm attempting to fix an AC problem and discovered this gray vacuum line in my truck isn't connected to anything. I saw a Youtube video where the guy connects it to a valve that my truck appears to be missing, or maybe it's located somewhere where I haven't found it yet. For reference, my truck is a '98 4.0 OHV xlt 4wd auto.

What I'm wondering is if some previous owner just capped off this line and if so, where and to what is it supposed to connect? Below is a photo of the line in my truck- notice the bolt screwed into the end of the L-connector to cap it. This gray line, along with a black line, run to the passenger side firewall underneath the blower box. Since I've owned the truck (4 years) this gray vacuum line has been just sorta flopped over the AC lines right about where I'm holding it. Thanks.

 

[RonD]

It connects to the heater hose by-pass valve which has been removed from your engine bay

It would be where the heater hoses have been spliced together, seen in your photo


I was only used in MAX AC setting to cutoff hot coolant from flowing thru the heater core
But it should be plugged, and looks like it is, or the recirculated air vent won't work in MAX AC setting

Bypass valve looks like this: https://www.oilburners.net/articles/pictures/valve2.jpg

The vacuum line would plug into the black cylinder on the top, and close the valve to cutoff flow thru cab heater core when inside switch was in MAX AC only

These often cracked and leaked, so were removed, outside of MAX AC cooling maybe losing a few degrees it doesn't effect operation of the vehicle at all


And just as a heads up, you should Reverse heater hoses, at the firewall, every few years to reverse the flow thru the heater core
It will keep it cleaner by back flushing it while driving, and its FREE to do, lol


Whats the AC problem?

 

[Dirtman]

Vacuum lines suck.

 

[avid]

These often cracked and leaked, so were removed, outside of MAX AC cooling maybe losing a few degrees it doesn't effect operation of the vehicle at all

Whats the AC problem?

Thanks Ron. That's good news about the gray line. I figured I would deal with it either when I noticed a problem or had to deal with the vacuum system, and it hadn't been an issue until today.

The AC problem is the AC stops blowing through the vents and seems to blow through the defrost vents when the engine is under load (accelerating, etc.,). It didn't blow through the vents today hardly at all while driving on the interstate, and that seems to be worse than even last week. From what I've read and searched this is likely a vacuum reservoir or check-valve issue. I've never had to do anything with vacuum lines before, and I haven't as yet been able to locate a new vacuum reservoir online.

But this is an issue I need fixed this week as I'm driving to Georgia next week with my wife and we're taking the Ranger. Needless to say my wife will kill me if the AC isn't working well.

 

[avid]

And just as a heads up, you should Reverse heater hoses, at the firewall, every few years to reverse the flow thru the heater core
It will keep it cleaner by back flushing it while driving, and its FREE to do, lol

That's a good tip, thanks.

 

[RonD]

So your AC problem is vacuum related but look at the BLACK line next to the grey line at the firewall

The black lines runs to the front of the engine bay to the Vacuum Reservoir, inside the cab this line is the Main Vacuum source, so with little or no vacuum all air flow goes to Defrost Vents, they are the default vents
When idling vacuum is higher, when you accelerate vacuum drops close to 0

Vacuum reservoir "stores vacuum" so vents in the cab stay on panel or floor when driving, or defrost if YOU want defrost, lol
(same as power brake booster stores vacuum)

That black line can crack or melt near exhaust, easy to repair with regular rubber vacuum hose of the correct size
The plastic vacuum line is just cheaper for car makers to use and color code if needed

The vacuum reservoir looks like a black ball, usually easier to see looking up and under in front of passenger side wheel well

These can crack and leak, the check valve is built into them in most cases, so there is a IN and OUT port

 

[avid]

So your AC problem is vacuum related but look at the BLACK line next to the grey line at the firewall

The black lines runs to the front of the engine bay to the Vacuum Reservoir, inside the cab this line is the Main Vacuum source, so with little or no vacuum all air flow goes to Defrost Vents, they are the default vents
When idling vacuum is higher, when you accelerate vacuum drops close to 0

Vacuum reservoir "stores vacuum" so vents in the cab stay on panel or floor when driving, or defrost if YOU want defrost, lol
(same as power brake booster stores vacuum)

That black line can crack or melt near exhaust, easy to repair with regular rubber vacuum hose of the correct size
The plastic vacuum line is just cheaper for car makers to use and color code if needed

The vacuum reservoir looks like a black ball, usually easier to see looking up and under in front of passenger side wheel well

These can crack and leak, the check valve is built into them in most cases, so there is a IN and OUT port

Thanks again. I will check the black line tomorrow morning when I remove the wheel well.

Regarding the vacuum reservoir, do you know if these are generally available to purchase new (maybe under a different name?)? I haven't been able to locate one at any of the regular parts stores with that name and my truck specs. I'm hoping when I remove the wheel well panel to get to it there will be a part number that might help me locate one. I'm not averse to visiting the local U-Pull-It, but I wonder if an old replacement would be much better in the long run than what I have now.

 

[RonD]

Use this Ford part number: F87Z-19A566-AA
Or try Dorman 47076

About $35-$45 at a Ford Dealer
Dorman about $25-$35

Fairly generic part not Ranger specific, so should be many at a U-pull, but it is in the front of vehicle, so............front end collisions aren't good vehicles to check, lol

Also a check valve if needed, but as said most have the check valve build in to one port

But just FYI, its usually the Black line between reservoir and firewall thats the problem

 

[avid]

Use this Ford part number: F87Z-19A566-AA
Or try Dorman 47076

About $35-$45 at a Ford Dealer
Dorman about $25-$35

Fairly generic part not Ranger specific, so should be many at a U-pull, but it is in the front of vehicle, so............front end collisions aren't good vehicles to check, lol

Also a check valve if needed, but as said most have the check valve build in to one port

But just FYI, its usually the Black line between reservoir and firewall thats the problem

Cool. Thanks again, Ron.

 

[avid]

Just to update: I went ahead and ordered the Dorman Vacuum Reservoir from Amazon (for I think around $12) just in case I needed it and waited until it arrived to open up the wheel well. So Friday evening I removed the wheel well and found the Vacuum Reservoir dangling in the cavity by one vacuum hose. The bracket that is part of the reservoir had broken off so it had just been bouncing around in that cavity for I don't know how long. The vacuum line to the firewall had broken off at the boot attached to the reservoir.

To get to the bolts that are supposed to hold the reservoir to the truck body I had to pull out my air box. The process itself wasn't too difficult- just a little bit of a PIA due to the location. Got the reservoir attached, used a 7/16" inside diameter rubber hose section to re-splice a break in the disconnected line, and reattached it to the reservoir. The most difficult part of the whole process was removing and reattaching the wheel well piece since my truck has those flares around the wheel wells.

Tested it out and it worked great: I never lost AC at any point while driving. And on the 1200-ish drive to Georgia it worked well the whole trip. Also, truck made it with no problems. This is the second long-distance trip I've taken the ranger since replacing the engine and many of the engine components a couple years ago.

 

[RonD]

Good work

Thanks for the update