A/c only blowing out of top vent

It's too dam hot for this. 103 degrees and my A/c will only blow out of the "vent" position. The air isn't hot (prob needs a charge), but what I'm really worried about is the fact that it only blows out of "vent" and no other position.

The slide that you use to change the air works well and the system doesn't make any strange noises, but I get NO air out of any other vent except the top one. It doesn't matter what I select, it only blows out of the top. It does this with the heat as well.

I keep joking with my wife saying that I'm going to open it and find a rats nest because it sat for 7 years...wonder if that's the cause

Vacuum leak. Start up front near the right headlight. Look for the black vacuum ball. Work your way back.

Thanks, I'll check it out today. I know nothing about auto a/c lmao

Always post up year, engine, etc.

The airboxes changed over the years.

Yes, you can start with the vacuum diagnostics, but USUALLY when you lose vacuum the system defaults to the defrost vents. When you say "top vents" do you mean the defrost vents?

As said, if your XJ hasn't been modified, the vacuum reservoir is on the passenger side, back of the front bumper. A common weak spot is where the vacuum lines run under the battery box.

Good luck.

I too have the same problem. The AC blows out through the vents but also comes out my defroster vents. I traced all my lines (from the black canister) and no tears or rips anywhere, including the canister. My jeep is a 2001 xj 4.0L with a AFN cold air intake if that matters. Any other ideas on where to check?

mako my day said:

Vacuum leak. Start up front near the right headlight. Look for the black vacuum ball. Work your way back.

Click to expand...

Does the cruise control work (if installed)? Could have a leaking motor actuator.
The black vacuum accumulator is located behind the front bumper on the passenger side. The plastic vacuum line goes under the battery tray over the fender well where it can tie into the cruise control motor (if installed) then goes toward the firewall and a small line taps off and goes thru the firewall near the A/C filter drier the main line continues along the firewall and connects to the intake manifold.
The most common location for the leak is the line under the battery tray.

Same/similiar problem on my 99 4.0. I don't have any vacuum leaks (just had it tested while replacing other engine components) and my system is fully charged. Air is nice & cold, but only directed at the windshield. In the morning before it gets too hot (mid 80s) it takes it a few minutes but usually switches over to the vents by the time I get to work (<15 min) with an audible "thunk" almost every time. If it doesn't "thunk" then it blows out both the defrost and the dash, slowly moving to the dash only. In the afternoon (temps of 100+ lately) I get nothing but defrost vents 9 times out of 10. The few times that is DOES switch over, the fan is on high (4) and it starts "whistling" so to speak, like there's something blocking the airflow, and then "THUNK" and I have A/C all of a sudden. I've also noticed, and this may or may not be all in my head, that coasting seems to help everything switch over. Under load, accelerating, going up a hill, etc. seems to delay/prevent the switch-over and/or, if there hasn't been a decisive "thunk", divert what little air may be coming out the vents back to the defrost.

Anything? Thanks!

-alopeks

alopeks said:

Same/similiar problem on my 99 4.0. I don't have any vacuum leaks (just had it tested while replacing other engine components) and my system is fully charged. Air is nice & cold, but only directed at the windshield. In the morning before it gets too hot (mid 80s) it takes it a few minutes but usually switches over to the vents by the time I get to work (<15 min) with an audible "thunk" almost every time. If it doesn't "thunk" then it blows out both the defrost and the dash, slowly moving to the dash only. In the afternoon (temps of 100+ lately) I get nothing but defrost vents 9 times out of 10. The few times that is DOES switch over, the fan is on high (4) and it starts "whistling" so to speak, like there's something blocking the airflow, and then "THUNK" and I have A/C all of a sudden. I've also noticed, and this may or may not be all in my head, that coasting seems to help everything switch over. Under load, accelerating, going up a hill, etc. seems to delay/prevent the switch-over and/or, if there hasn't been a decisive "thunk", divert what little air may be coming out the vents back to the defrost.

Anything? Thanks!

-alopeks

Click to expand...

In the line that goes thru the firewall there should be an inline check valve that keeps vacuum onthe motor actuator so that what you described doesn't happen. This was an updat that was done on 97-99 XJs. The later Jeeps had it include from the factory.

Is there a fix/replacement part for this? What would you call that part, and where exactly should it be located?

Sorry, once we're past the basic maintainence/modification/engine work, I get really ignorant really fast... Thanks!

-alopeks

It's called a check valve as far as I know,

Quick google search and it's a $5 universal part at Autozone...

Looks like I'm headed there on my lunch break! Thanks! (Fingers crossed)

-alopeks

Right now I have the dash pulled out of my XJ chasing a similar problem except that on my XJ everything work fine until accelerating or using the cruise control and going up an overpass or hill then the ac blows only from the defrost vents. All the vacuum lines check good from the canister behind the bumper all the way to the control in the dash. That is as far as I can check without proper test equipment. If I were to single out a single item it would be the control with all those tiny hoses coming off it. On a 17 year old XJ, we have to be prepared to replace many questionable or defective parts.

Funny, I remembered replacing that same part some 5+ years with one from a bone yard to solve the same problem. This time I need a new part (what ever the correct name is).

By-the-way, the vacuum drop to zero shortly after the engine is shut down. That is a dead give away that there is a leak some where in the system.

The most common cause of the vents being stuck in the defrost position is a cracked vacuum line through the firewall. Its such a tiny brittle line ons a 97-99 that it will break at some point. Its happened 3 times on my xj. I finally ran a slightly larger new line all the way from the vacuum connector to the vacuum switch

altrocker1 said:

The most common cause of the vents being stuck in the defrost position is a cracked vacuum line through the firewall. Its such a tiny brittle line ons a 97-99 that it will break at some point. Its happened 3 times on my xj. I finally ran a slightly larger new line all the way from the vacuum connector to the vacuum switch

Click to expand...

I will look at that line.

My advice is to get yourself a vacuum gauge. Start at the Manifold. Take a reading, at idle, to see what you are working with. From there, chase out the lines taking a reading at every available junction point. The leak point will become obvious.

A side note here:
When I fitted the Cruise Control into my Heep, I found the idle vacuum to be on the low side. It eventually traced to the vacuum reservoir (ball under the front bumper). After giving it a "reseal" job, picked up a good 2"Hg of vacuum.

It was resealed by giving it a light coating of fiberglass resin while it was under vacuum. The vacuum was generated with my brake bleeding tool. Even though the cracks were not visible, it was leaking.

Another prime leak point is the rubber fitting at the reservoir itself. If the reservoir has been relocated, it is not unheard of for the fitting to leak. With age, the rubber hardens and when the connection is broken to move the reservoir, the old fitting does not seal again. A very small tab of silicon gasket maker will seal it up nicely.

Check Valve had a small leak, and I replaced it, but now I NEVER get A/C except through the defrost vents. Checked the line thru the firewall and it appears to hold vacuum, as does the reservoir, which was relocated years ago. This issue is only a few months old, so I don't think it's that, either. Engine isn't surging, and the cruise control works just fine. Mechanic friend says it sounds like a bad control switch, which of course is a crapload of money because it's one solid-state unit. Any ideas on how to fix that instead of replace? Anything y'all think I'm missing? It's been above 100 degrees every day for over a week; this is getting old...

-alopeks

alopeks said:

Check Valve had a small leak, and I replaced it, but now I NEVER get A/C except through the defrost vents. Checked the line thru the firewall and it appears to hold vacuum, as does the reservoir, which was relocated years ago. This issue is only a few months old, so I don't think it's that, either. Engine isn't surging, and the cruise control works just fine. Mechanic friend says it sounds like a bad control switch, which of course is a crapload of money because it's one solid-state unit. Any ideas on how to fix that instead of replace? Anything y'all think I'm missing? It's been above 100 degrees every day for over a week; this is getting old...

-alopeks

Click to expand...

If you had occasional A/C previously and now after replacing the leaking check valve; you have none....
Don't take this the wrong way, but are you sure you installed the check valve in the correct direction?

Actually, yes. And when it didn't work, I switched the direction. Still didn't work, I switched it back and got online to verify it. It's in right, and holds vacuum perfectly.

I'm afraid it's a case of broken vac line(s) behind the dash, which I REALLY don't want to spend time hunting down... Wondering if there's another possible fix I'm just missing somewhere... Thanks!

-alopeks

To try and pin the problem down you may try this:

See pic.

On the Heat/AC panel, select Off (O) on the mode selector. Hook up a brake bleeder vacuum pump (cheap at Harbor Freight) to the HVAC vacuum coupling at the intake manifold and pump the system down to about 15-17 in.Hg. and see if it holds for several minutes. If it does the system is tight, including the vacuum supply line from the firewall tee/check valve to the mode selector. If not you have to chase the leak. If all the lines and components in the engine bay appear to be okay, check the operation of each HVAC Unit door.

Do this in a quiet environment...

With the system pumped down (keep it pumped down for tese tests), move the mode selector from Off to Max (#11 in pic), then to each mode in rotation (#10 thru #5 in pic). If when selecting a different mode you do not hear a door actuator move, that door actuator is inop, or the mode selector is defective. Or, if at any mode selection you cannot pump the system down again, the vacuum line for that door actuator is leaking.

Any fix under the dash will be a PITA.

Mode selector:



Hook up at intake manifold (engine removed - no manifold. LOL):

Okay...

Went back through with a passive (only one in stock) vacuum gauge from HF. Good vacuum at all lines, but only AFTER I replaced the BRAND NEW rubber connector for the check valve. The new one split right down the middle. Afterward still nothing, so I disconnected the vac lines to the control switch, and each one had a decent amount of pull. Reattached everything and kept on driving. Now the vents work pretty consistently, but only after a few minutes at least. Seems to open the vents faster if I've driven more recently, but that could be in my head... I'm not sure what I did to fix it... There's some kind of oil/sealant/residue on the inside of the control switch. Maybe disconnecting and reconnecting moved enough of it around to recreate the seal? Who knows... Thanks guys!

-alopeks