HVAC stuck (mostly) on defrost

[TxGator]

Before I begin let me say that I did search and didn't find my exact issue and wanted some clarification on fixes/diagnosis anyway.

(2006 Jeep Liberty Sport)

So here's the problem.....

My HVAC fan works on all speeds (1-4) but the directional options (face, face/feet, defrost, etc) doesn't work -- most of the time. That is to say that in some instances some of the settings will work, partly. Like on the way home yesterday I could get the "face" vents to blow a LITTLE air out, but not the correct amount. The rest sounds like it's blowing in the dash, behind the glove box.

When I got home I opened the glove box and looked behind it to see if something had come loose. Nope. I also checked under the hood for any obvious problems. None. I then shut the hood and tried the face vents again. They were working about 80% of the normal volume. So I turned everything off and tried again. At this point it was stuck in defrost again.

So, I've searched and searched and haven't found a DEFINITIVE solution. But I did see a couple of posts in these forums which mention the vacuum line. This sounds like an easier fix as the other "fixes" indicate full dash removal

So my questions are:

1. Is my problem a vacuum line leak? If you think so, with what certainty.
2. If this is a vacuum line leak is this something I can test for? Fix?
3. Would any of the handheld diag computers (like they use at AutoZone) be able to tell me where the failure is?

If there is any additional info that I can provide you with that will assist in troubleshooting/solving my problem please let me know.

Thanks.

Oh and BTW...I am no mechanic by any stretch of the imagination but I am comfortable with changing my own oil, filters, and brake pads (that type of thing).

 

[kb0nly]

I helped troubleshoot the vacuum controlled switch on a minivan last year, it was a pain in the ass. But if you have some time and some tools its possible. The main things we had that were helpful were a vacuum gauge which we used to check the supply line to the control for vacuum, and a small vacuum pump that we could use to apply vacuum to the control independent of the engine.

We connected the vacuum pump to the control and turned on the key but didnt start the engine, turned the blower on high, and found we could cycle through all the settings and the control moved fine, so knowing that was ok we put the gauge on the supply line from the engine and checked for vacuum and there was none... From that point on it took an entire day of tracking the line out through the firewall and checking every vacuum line underhood until we found a break in a line.

Its notable though that this engine did also have a stumbling idle, though it never turned on the CEL. It was thought it needed plugs and wires, but after fixing the vacuum leak that was affecting the heater control then the engine smoothed out. Are you having and problems with rough idle or any other indication of a vacuum leak?

Also, on here not too long ago there was a post about a broken blender door arm, if you pull down the drivers side of the dash below the steering column you can see the vacuum actuator on the side of the airbox, with it running and moving the control between settings you should see that move, is it? If the actuator arm is moving you might also want to check that its not actually broken, i will find that post and link it in a few.

 

[kb0nly]

http://jeepkj.com/forum/showthread.php?t=43252

Here you go... You know reading Tony's post again it sounds like you have the exact same problem since its mostly stuck on defrost.

 

[TxGator]

Ok -- update. I read and reread that post and without removing the dash cover and door I looked at the "actuators" (plunger looking devices that open and close to open/close vents) and can see that, on the driver's side at least, there are 2. And both have the posts in tact.

So, I turned the HVAC on high and since it's all coming out of the defrost turned the setting to match. I then pressed, by hand, the lower plunger in. This directed all of the air to the floor. I repeated this a couple of times and finally decided to "match" the control setting to floor while I was holding the plunger in.

From this point on if I SLOWLY turned the control dial the plungers would operate properly but VERY slowly.

This tells me that the computer side and mechanic side is fully functional -- YES?

Maybe they're just stuck and need some lubrication?

Could this be a sign of a vacuum leak, where under certain conditions there is enough pressure to open/close the plungers?

At least it appears I can heat the car today...since it's in the 30's today.

Any suggestions on a permanent fix?

 

[kb0nly]

Sounds to me like you don't have enough vacuum then if they are moving slowly. The fact that you can move the arm and make the airflow change means the blend door arm isn't broken then. It could be a bad vacuum actuator too but i haven't seen any reports of one of them failing.

I would pull the dash bezel off, the heater controls will come off with it, check the connection on the back of the control to make sure its not a simple loose connection and a leak.

You should be able to hear if the control is leaking also when you have it apart, should hear air movement. You can also do something as simple as light a match and blow it out by the back of the control and see if the smoke gets sucked in anywhere, indicating a leaky connection.

You could try some dry lubricant on those arms but i wouldn't think they would be getting stuck as there is enough play in them, they aren't really tightly fitted pieces if that makes sense. It would appear Defrost is the default setting on the KJ, that is vacuum pressure is required to move the actuator off of Defrost to any of the other settings.

 

[TxGator]

Update Part 2

So....after manually opening and closing both "plungers" the system seemed to function properly for a short time. Then the system was turned off and left that way overnight. Cut to this morning, early, about 35 degrees out. Started the vehicle and headed out on about a 30 minute ride. The system was again functioning properly. Arrived at the destination, turned the car off for about 10 minutes and when I started it again, the problem was back.

So, leaving the car running and the HVAC system in FLOOR mode I crawled underneath the dash again and tried to manually "free" the plungers. I was able to move them by hand but no matter what setting I placed the system in it seemed that that always wanted to return to where they were (defrost).

So, I figured I would listen/look for a vacuum line leak. I popped the hood and began looking around...

Nothing...

Nothing...

...and then...

I SEE THIS

You must be registered for see images

What in the HECK? I mean really, it's cold out but it isn't that cold. And the engine is more than hot. So why the 1/4 layer of frost on whatever component this is? (Compressor?) And if this IS the compressor, why is it running when the HVAC system is set to MAX HOT and the A/C button is OFF?

Can anyone help me out here? I REALLLLLY need to see if this is something I can fix so I can save money and if it isn't something I can fix I need to be educated enough so that I don't get screwed when I take it to the shop.

HELP!!!!!!

 

[JeepJeepster]

What year is the Jeep? On 05+ kj's the A/C runs when the floor position is selected. Hence the reason the accumulator is covered in frost.

 

[TxGator]

2006. So I guess that answers that part.

Any idea why the plungers/dampers that control the air flow direction would stick/not work at all?

Any idea if this problem would show up on a handheld diag computer?

 

[kb0nly]

Yep normal, when in defrost the AC compressor is run, so the accumulator/dryer gets frosted up like if you were running the AC in the summertime.

I'm starting to think its a bad actuator... But without trying to swap parts the best i can say is bring it to a dealer.

 

[moparman]

I think the AC compressor runs in every mode except face vents. Anybody but you been under the hood? Seems like a vacuum hose is pinched off.

 

[TxGator]

This is driving me nuts.....

No one but me has been under then hood in over 18 months.

The problem continues, sporadically

How can I test for a vacuum line leak or pinched vacuum line?

I've order the Haynes manual for the 06 KJ.....

In the meantime....any suggestions?

 

[kb0nly]

One thing i have done to find vacuum leaks is to take a propane torch and turn it on, DONT LIGHT IT, you just want gas coming out... Then you run the tip of the torch along the lines and around the vacuum line fittings and such. When you find the leak the engine will suck in the propane and you will hear the engine speed increase.

Pretty old school technique but it works. If you got a smoke generator that works too, thats the way they do it now days.

 

[pontipine]

Any resolution on this?
I have the same issue. It doesnt happen very often in my case. Usually after driving more than 30mins, or pulling a trailer.
The actuators are very slow in my case as well. They take several seconds to transition.
I have added a vacuum gauge tee'ed to the incoming line under the glove box to see whats going on.
Vacuum is 15 to 20 inches when its behaving well.

 

[pontipine]

Update. Vacuum gage drops to 10 when misbehaving and moves around quite a bit when changing the air flow selector. Putting it on circulate for a few seconds seems to restore functionality.
The check valve behind the glove box is ok. Maybe a leaky actuator or selector knob.

 

[07 liberty]

I had a similar problem with my 07. Air would only come out the defroster vents. Opened hood and found a vacuum line closer to drivers side running horizontally along the fire wall that had sagged a bit and melted a small hole in it. I spliced it and put a plastic tube inside each spliced end and all was well. Would attach a pic but I no longer have that jeep. Good luck.


Sent from my iPhone using Tapatalk

 

[pontipine]

Thanks for the tip.
Switching to recirculate no longer works. Drove home last night with no defrost or any other. Fans can be heard working at all speeds, but only a tiny amount of air leaks out anywhere. Very annoying this time of the year.
Last time I caught it doing this there was a noticeable vacuum drop, but not a complete loss, and the actuators were dead slow.
I will look for a damaged line in the engine, but I would expect this would cause problems all the time, not just 20minutes after starting. It always works fine when started cold. It only seems to fail after running for a while.
Anybody ever have to change the selector switch/valve?
Would there be any need to add some pneumatic took type oil to the system to keeps the seals happy?

 

[Porkchop]

If I understand what your saying and the fan isn't running I would check the blower motor resistor.