On my son's '97 Ranger a few moments ago, one of the vacuum lines simply came loose from the vacuum bowl (or vacuum canister) directly down underneath the air cleaner. popped it back in and viola.

 

I am having this issue with 2000 3.0 Ranger. If I am going up an overpass and have low engine vacuum, the air defaults to the defrost. I have disconnected the hose going to the AC controls through the fire wall and tested from that connector, through the vacuum reservoir and to the check valve on the engine. It all held great.

I am worried its the hose where it disappears under the blower and airbox assembly to go through the firewall. I have lightly tugged on it, and it didn't pull apart, so it is attached to something under there, but there is no room to look at the condition of the hose.

Does anyone have a picture of what the firewall connection looks like from the under hood side?

I am also wondering if it might be my control assembly under the radio finally wearing out.

I didn't think to check the heater bypass valve for a leak. I will do that as well since I just noticed the other night it wasn't responding.

 

Okay, my heater valve is working correctly. I disconnected the vacuum hose harness that's behind the glove box on the left side. With the truck running, I found the port with vacuum coming from the engine bay and put a gauge on it. Steady 15". I shut the truck off and it held a steady 15" with no loss over a few minutes. So, my leak is more than likely in my AC controls. I just have to find the motivation to pull the stereo out and then pull the control console and do the checks on it.

 

Pulled the A/C controls out. Ports on back of the switch are labeled 1 thru 6 with #1 being the vacuum from the engine. Hooked the gauge up to port #1 on the harness for the switch and started the truck, 15" of vacuum that held after shutting the engine off again. Ports 2-6 on the truck's harness, with one of them not being used all were able to be pulled to 20" of vacuum and held like a rock. So my guess is my switch is bad. Using the factory part number on the switch, I tracked it down to a Motorcraft #YH1487. $25 on Amazon. It will be here in 2 days.

If you need this switch and its a different part number, go to rock auto and search under your year and model in "Electrical-Switch & Relay" and then under "blower switch" and you can find the original OEM part number in the brackets for the description of each switch available.

For a 2000 Ranger, it is #F87H19D961AA

 

I must have missed one port in my trouble shooting......

It turns out the hose that holds the incoming air door over to recirculate also goes to the heater core shut off valve.

After swapping the switch on the dash, it was still doing all the same issues, so out of desperation, I pulled the passenger inner fender. Looking all over, I found the hose going to heater core valve had a chalky looking spot. When I wiped it, that area of the hose fell apart, so it was one half of the hose, about 1/2" long gone.

I put 3 layers of heat shrink on the whole length of hose after inspecting its entire length and couldn't find any other bad spots. I now know that you can pull the bulkhead fitting through the fire wall into the passenger compartment easily after looking at it from the engine bay. Its just a grommet.

There's plenty of slack on the hose going to the vacuum canister and you can pull the hose off of the heater valve and pull it completely off, into the passenger compartment and replace if need be, without pulling the inner fender. If you need the change the hose going to the vacuum canister on a 2000 ranger, then the inner fender has to come out.

After plenty of uphill and heavy throttle driving, no more A/C issues and now, both the recirculate door and the heater valve stay in the correct positions even after the engine is off, so the system is now holding vacuum correctly.

 

My 2004 Expedition seem to be doing this as well. We get Air thru defrost but not on anything else. Changed switch on control panel and still the same. Can someone explain to me why the compressor comes on for defrost but not for ac or could it be the vaccum lines l see alot referring to in thread. Changed vac lines under hood but not under dash yet.

 

Good gravy there's a ton of info missing here..............

Which switch did you change---and why?

Which under-hood vacuum lines were changed---and why?

Defrost mode is somewhat of a safety feature so the A/C compressor engages to dehumidify incoming air---windshields no longer fog over like they did many many years ago before A/C was so common on vehicles. Since comfort A/C isn't a safety concern if the air flow cannot be diverted to the dash vents the compressor won't engage. This MIGHT be due the electro-vacuum switch being defective (slight chance) or there is no vacuum signal to that switch (bigger chance).

Vacuum signal to the air flow ducting system comes off the throttle body in a small hard plastic line that is highly subject to breaking. Age alone can cause this, fumbling around in the engine bay can be a cause also. (I've done that.)

So first step is determining if you have a vacuum signal to the duct control system. I'm not familiar with the Expedition but here's a diagram of an E-Series that might be helpful in your situation:


If I'm mistaken about anything here someone will correct me. I'd also post this as a new thread in the Expedition sub-forum here on FTE.

 

Im not a mechanic so l can only refer to what little info l know. Theres some gray tiny plastic wires no more than three far as l can see under the hood near battery l was told were vaccum lines that air/heat goes thru were broken to were u can hear the air coming out. We cut the part that was broken and changed them. On my 04 model expedition l have the manual ac/heating control panel with the 3 **** switches and the third switch towards right would be the one that allows u to turn it (from left to right) max ac, floor, etc, off, defrost floor, defrost..so that would be the switch lm referring to that we changed be it the compressor would come on ONLY when the switch is on defrost but soon as we turn it back towards the left to all other components compressor politely clicks off just giving us fan air if u will.

 

Your issue is most likely centered on the Function Control, the one that is supposed to switch between A/C, Defrost, Vent, Off etc etc.

That particular switch has an electrical portion and a vacuum routing portion too, they work together to effect and direct air flow and compressor engagement as commanded.

 

Thanks alot. We will definitely be checking into that

 

I found the same thing and also fixed the problem. THANKS!

 

Did you solve it yet?

 

Well, he's had almost three years to figure it out...

 

Can someone tell me where the other end of the broken line, with the yellow circle, plugs into (when it's not broken?) I was replacing that line and disconnected it.

I've searched the firewall but don't see an obvious location...a picture would be great...i have a 20014 Ford Expedition.

thanks a bunch!

ANSWER: this line plugs into a much thinner black line which comes out of a firewall grommet (behind the battery)...there is another line in a corrugated plastic protector that also enters the same firewall grommet.





Cracked vacuum line behind battery on 2000 f150 4.6L[/QUOTE]