A/C problem vacuum leak, help finding please.

[tx_ag_97]

Vehicle: 2004 Expedition, small V8 (can't remember size, 4.9L maybe).
Problem: When A/C is on it will blow to defrost when RPM +1k, then will switch back to blowing normal when under 1k RPM.
Reason: Leak in my vacuum lines somewhere (or so I've read).

Questions:
#1) Which lines are my vacuum lines? Pics or web links much appreciated.
#2) Where would this leak most likely happen? Joint? middle of hose?

I am by no means a mechanic, but I am comfortable changing all fluids, alternator, brakes, etc, minor stuff. So you'll have to pardon my ignorance as to which lines to examine.

Thanks for any help.

[tx_ag_97]

/bump
no one knows of a website that has schematics so I can figure this out?

[buxter]

I doubt it's the vacuum lines they have to do with the engine in general, not the AC blowing warmer air.

I would check and make sure that you have enough refrigerant in the system and go from there. I would invest in one of those HANES manuals.

[Bart Peluso]

Haynes manuals are almost useless . I bought one and its pretty bad when it comes to diagnosis of problems

[phantom_smack]

The vacuum hose is probable cracked or broken in the engine compartment by the battery.It is a black hrd plastic line.Have you changed the battery lately?The acid from the battery usually gets to the plastic hose and when you change the battery and move the line it can crack.

[tx_ag_97]

Thanks Phantom, I'll check that area tonight.

[drob]

I finnally stopped mine from switching. I added a vacuum tank, NAPA part No BK7301605.

I had read about phantom_smack solving his problem the same way. ( Vents switching under engine load and losing vacuum because of a failed check valve.)

Tank cost about $13 and is about 6 inches in diameter, plastic with two nozzles and an internal check valve.( If you draw on the nozzle, without the hood, you will be able to draw air---but you will not be able blow through. This is the nozzle to connect to the engine side.

I removed the inspection cover on top of the dash to watch the valves move. There is a1/8 inch black rubber vaccum line, on the left side of the engine coming out of a block with other lines. There is a connector in the line. First, with the engine idling, I operated the slide control to turn on the air conditioning, and watch the valves move in the dash. Then I pulled the vacuum line loose and operated the slide control again, and when the valve did not move---it was the correct line.

I used another piece of 1/8 inch tubing, about 6" long to connect the tank to the line from the block . Drilled a small hole through the tank mounting bracket and tied the tank under the hood with a piece of wire. Connected the line going to the dash on the other tank nozzle.

[tx_ag_97]

I forgot to update this.
I found the cracked vacuum line, it runs from under the battery into the firewall. (My cracked battery had oozed acid onto it.) I took the line off (unrepairable, too many cracks) and took it to dealer but their is no exact replacement. Instead they gave me a rubber (not plastic) hose slightly larger, but slipped over the ends of line where I cut it.

**One word of advice, do not try to find where the line connects at the firewall. Instead cut the line outside the firewall and make your splice there. Problem I had was I tried to find where the joint was inside at the firewall, and well the T-joint fell down inside the firewall when I disconnected it. Luckly, I was able to fish it out after about 30mins with a set dental forceps and a lot of verbal encouragement. But trying to hold the T-joint and connect the new line was a royal pain too. Don't do it, what was a 5min fix ended up taking about an hour. Just cut the line and leave enough so the new hose can slip over it.