First post here, long time lurker. I purchased my second XJ Jeep with the 4.0 and this one has a bunch of issues but the AC issue is problem number 1 due to a pregnant wife and Florida heat. I only get air out of the defrost in the cabin. I'm aware that's due to a vacuum leak. However, somebody before me has been futzing around in the engine and items are missing so I'm having problems trying to find part numbers and locations. I'll upload a couple pictures. My goal is to first get the vac leak fixed THEN find out why the AC is only blowing warm air. The red circles show the previous guy/gal's handy work. I would appreciate any help directing me to part numbers or names. There are two or three plugs that don't seem to fit anywhere on the passenger side by the fuse box under the hood as well. I did order Dorman 47170 check valve but I'm not sure that's the correct valve for the T on the passenger side circled in the pic. The picture with the writing in it has the parts I need but I can't seem to find them. Also, the line that comes off the T is missing so I'm not sure where the other end goes. Thank you all in advance.

 

Need to post what year Jeep XJ you are working on. You are correct that air blowing only out the defrost vent is a vacuum issue. There should be a black ball looking reservoir just under the front bumper on the passenger side. The vacuum connection comes off your intake to the firewall and runs over to where your heater lines run through the firewall. At that location there is a "T" with a small black vacuum line going through the firewall to your AC selector (not a direct run, to be fair). The vacuum line then runs to the passenger side fender where is you have cruise control there is another "T" that connects it to the vacuum system. From there the line runs to the reservoir I spoke of earlier.

You can also go to cruiser54.com and download a fsm for your year model and a parts manual as well, between those you can see the vacuum diagram for yourself.

Also do a search of the site, you will find threads that probably will address your problem many time over
Like this one: https://www.cherokeeforum.com/f2/wha...-break-258949/ That has some good pics in it.

 

Thanks for the info. It's a '98 by the way. I have the vac diagrams from other postings but I can't find any part numbers.

 

I got all my parts at a local U-Pull it parts place. On your XJ, from the engine bay, look to where the heater hoses go through the firewall. If you have a hard plastic tube sticking out......you have good luck! Just find enough tubing to connect to the "T" right above it and then follow it both directions from the T and make sure it is connected and doesn't end in a open hose. You have to have a sealed vacuum loop to get the AC control to work to change the air to where you want it. Should start/end on the intake on the drivers side and the other end terminates behind the bumper in a hard plastic sphere that is your vacuum reservoir.

 

Nothing coming out of the firewall. I know what should be there, but it's missing. From one of the diagrams I have there appears to be a missing servo? Next to the fuse box under the hood. Also, what is that other hose coming off the firewall. The lower one seems to be an ac drain, but the other one is a mystery to me.

 

Maybe I should approach your post in a more logical sense......
In your first pic, I am not sure what that is disconnected.
In your second pic, that line marked "vacuum to Hvac mode" is the one that goes through the firewall by the heater hoses. If it is sticking out from there into the engine bay, you are a lucky guy! Just find a line that will bridge the part from the "T" to it...the one plugged by the screw.
In your third/fourth pic, I am not sure where that one goes, but it is not part of the HVAC vacuum line.
In your fifth pic, the screw is blocking the port on the "T" that goes to the hard black plastic line that goes through the firewall by the heater hoses and makes your vent selector work. The open hose below that appears to be a cut off drain for the AC condenser, as it should turn downward.

If it will help you, after you locate what is missing I can take pics of mine...its a 99 but essentially the same.

 

The servo is for the cruise control. If you have controls on the steering wheel, then someone removed under hood parts for the cruise most likely. Does your horn work? Is your airbag light on?

 

Mine had a similar defrost-only condition and it turned out to be the plastic vacuum line going through the firewall had broken just inside the engine bay from age deterioration. I repaired it with a piece of rubber hose and got my HVAC control back.

 

The horn does not work but I don't have cruise control options on the wheel. Curious that you ask about the airbag light. It isn't on but two days ago all of the electrical in the dash went out except for the speedo and tach lights. AC controls didn't work, radio didn't work, and the airbag light was on. Then, later on, it all worked. There was a burned/melted fuse in the fuse box under the hood that I've since replaced so I'm not sure if that was the cause. The fuse is unlabeled but it was a small 20 amp. I'm still curious where that cut hose traveling across the firewall is supposed to go and if a vac diagram is available. A pic of somebody else's 4.0 around the same year would help me greatly.

 

That hose, if it's the (approximately) 1/2" diameter one with the open end deformed into a rough hex shape, is a fuel system vent hose that ends exactly where it is now but at one time had what I think was a check valve inserted into the end. Mine looks identical, also missing the check valve.

 

I was wondering about the horn,cruise and airbag light because they all go work through the clockspring in the steering column. I will try and take a pic of then engine compartment of my 99 tomorrow.

There might be a way to push a vacuum line through the firewall wire loom on the passenger side and then connect it to the black vacuum hose connector behind the glove box. On the engine side of the firewall it would need to connect to the "t" and the vacuum line would need to be connected to the intake (source) and the reservoir behind the bumper. Stay tuned....I have not done what I suggest, but my vacuum line is pretty brittle and I have been game planning what to do if it has to rerouted.

 

All of the above is spot on. In your first pic, that connector is for an optional ambient temperature sensor, which you wouldn't have unless you have an overhead console with the temp gauge in it. Also that larger hose coming up from underneath is a vent line coming from the transmission. It should have a check valve on it to prevent moisture from entering your transmission. It doesn't have anything to do with your vacuum system and current problem.

 

I was wondering about the horn,cruise and airbag light because they all go work through the clockspring in the steering column. I will try and take a pic of the engine compartment of my 99 tomorrow.

There might be a way to push a vacuum line through the firewall wire loom on the passenger side and then connect it to the black vacuum hose connector behind the glove box. On the engine side of the firewall it would need to connect to the "t" and the vacuum line would need to be connected to the intake (source) and the reservoir behind the bumper. Stay tuned....I have not done what I suggest, but my vacuum line is pretty brittle and I have been game planning what to do if it has to be rerouted.

 

Mine is also very brittle. At the moment the original tube exits the firewall into the engine bay by about 1/2 inch. I carefully slid a piece of rubber tubing onto it and slid the other end onto the end of the original tubing that broke away from it (source line). It's working fine so far. If it breaks again at the firewall I'll have to cook up a new scheme. I used to run wire harnesses in motor cycle frames. To do that I'd use a length of carpet sewing thread, compressed air and vacuum to coax the thread from where I inserted it to where I wanted it to exit. Then I'd tie the thread at the entrance hole to the harness and pull it through the frame, not unlike using a fishtape to pull wires through electrical conduit. I might try that with the original (brittle) vacuum line where it terminates onto the HVAC controller plug, coming from the engine bay, and see if I can pull some rubber vacuum hose through the firewall.

 

Just replace the hardline all the way from the T to the mode control **** on the heater control console. You can buy some at any good auto parts store and thread it thru from the firewall side. Connect it with short pieces of rubber hose on both ends to the original ones. The reservoir is necessary so the settings don't change under acceleration and to close the heater doors when you shut off the engine. Any reservoir will work, even if it's not from an XJ and it fits somewhere.