Little/no air flow

[HoosierJeeper]

Having an issue mostly similar to this. No air comes out of the vents, can hear the blower running. Although mine doesn't blow anything from the defroster (like the below thread). I can change the positions and it changes the flow except nothing really comes out (but face only for example, the trickle comes out of the proper vents) It was working perfectly fine and has been (except for one instance I'll explain below). Tried recirc and it didn't change it, although I didn't run it in recirc for long at all.

http://www.jeepkj.com/forum/f196/hvac-stuck-mostly-defrost-43513/index2.html

About a year ago it happened on a road trip (like today). Then after a couple of hours of running it blew a piece of paper out of the floor vent. Not sure if this is the same thing, I will check to see if there is a blockage at the recirc screen. I haven't heard any vacuum leaks.

Thanks for the help...

 

[nullptr]

Pull down the glove compartment and check that the air intake behind it isn't clogged.

 

[HoosierJeeper]

Just drove it again and it worked perfectly. The change between positions is instant so I don't think vacuum is an issue. Checked the screen behind the glove box and didn't see any obstructions. I'm wondering if longer drives do something that causes it to act up?

 

[M38 Bob]

I'd bet on an intermittent vac leak.

Bob

 

[HoosierJeeper]

How could a vac leak be intermittent? Not challenging it but if there's a split in a hose wouldn't it always be the same? I was thinking some blend door got stuck....maybe due to low vacuum I suppose.

 

[M38 Bob]

One of these ain't all that expensive. Hook it up to the vac line going through firewall, watch the gauge and see if it shows a leak.

http://www.mityvac.com/hq_images/MV8000.jpg

The cats ass for one man brake bleeding also.

Bob

 

[CzarKJ]

I had a vacuum leak when the engine was under load and would come and go every hill I hit. Was different though since it went to default (which is defrost).

 

[HoosierJeeper]

Is it normal to hear a slight hiss sound whenever different positions are selected? It changes positions relatively quick, within a few seconds.

 

[TwoBobsKJ]

Is it normal to hear a slight hiss sound whenever different positions are selected? It changes positions relatively quick, within a few seconds.

Mine hisses a bit when I switch the vent positions. Was hoping the sound was unique to mine :icon_lol:

Bob

 

[Birdman330]

I've heard this is an electrical issue, what you described actually happened to me a couple times. Once when I started having issues with the ETB and the ABS Sensors, when it was dying on me at random times for a few days. Also happened when the ABS went bonkers on me in Atlanta and I had to run without A/C for a while because I thought somehow I froze up the entire system running the A/C. Problem didn't actually straighten itself out until I fixed the ABS Sensor hook up under the hood, it came loose and got too close to the engine. Once I hooked it back up all my problems went away.

 

[ltd02]

Is it normal to hear a slight hiss sound whenever different positions are selected? It changes positions relatively quick, within a few seconds.

Mine hisses briefly until it gets there, so to speak. arty52:

 

[HoosierJeeper]

That's how I'd describe mine I suppose...

 

[M38 Bob]

Yall ol boys sure ya ain't got a snake denned up up in thar?:icon_lol:

Bob

 

[Tin Man]

I've run into the same problem and I'm getting desperate. Fan is working ok but no air is coming out. This happens only when engine is warm, takes about half an hour before the air flow gradually drops down to nothing (no sudden changes). Changing the position from window to vents and to feet changes nothing. The recirculate actuator is still working and the latch is always moving as it should. Blend door as well but that's electrical, not vacuum operated (3.7L -05).

So far tested vacuum leaks from the line under the hood going through the wall and there's no leaks, at least when cold. I don't yet have a gauge but when testing with finger from the test valve behind glove compartment I can't tell any difference when the problem is active compared to when air is flowing normally.

Only thing I can think of is one membrane out of the three vacuum operated actuators that close and open the feet/window/vent duct latches starts to leak when heater core warms up and all three loose vacuum. I've tried to avoid tearing down the dashboard but I guess there's nothing else to do.

Before that I'd like to hear confirmation from anyone who has had this same issue. I'm sure I'm not the only one. I suppose these actuators available as spare parts so I don't have to replace complete HVAC?

 

[Billwill]

The Blend door adjusts the ratio of hot air to cold air and is electrical....uses a stepper motor. The control of which vents the air should come out is vacuum driven....a pipe from the intake manifold on the gassers and a pipe from the vacuum pump on the CRD.
If this vacuum pipe falls off or has a leak then the output flow of air into the cabin defaults to demister only. I had this problem when the Dealers knocked off this vacuum hose on my CRD during a service.

Does your Blower Motor blow well on all speeds?
Weird how this fails when engine gets hot.

You can observe the Blend door action by removing the glove box.

While you are there...there is a metal grid on the firewall which you can see to the right of the glove box. This is for the re-circulate feature and is supposed to allow air to escape outwards from the cabin.
This vent gets clogged up with dirt and dust...a good brushing and use of a vacuum cleaner helps to clean the grid.....worth giving it a try as it may help your problem!

 

[Tin Man]

Blend door is working perfectly and there's nothing blocking the air flow (even took the grid out and washed it). Actually blend door can't even block the air flow since it's one motor that changes the air flow from heater core to a/c and back and either of the doors is always open. The blend door motor is a common failure as well but usually the symptom is only hot or cold air.

It's the vacuum operated mode doors which cause this problem. Fan is operating normally and the fan speed changes when changing the position from 1 to 4. You can hear it even when there's no air coming out. I found out, that it may be possible to check the vacuum system by removing center bezel only. That's pretty doable compared to taking the whole dash out. I'll try that next.

 

[Tin Man]

Quick question which may or may not be related to this issue. What the heck is the vacuum line going into air intake case, just below air filter? It comes from intake manifold, there's a T-joint that splits line to HVAC and air filter box. It must have some function but what? See attached picture.

 

[ltd02]

Just a crankcase breather tube. Not vacuum.

 

[Tin Man]

I think I have finally cracked this puzzle. I believe the root cause is A/C low pressure switch which is not working. It keeps the compressor churning all the time and eventually it freezes the evaporator and no air gets through it. At least the symptoms fit: it takes a while before any loss of air flow can be observed. Then the air flow gradually vanishes as more and more ice build up on the evaporator until it is completely blocked. Turning the motor off for 15-30 minutes is then enough for ice to melt before air flows again.

I'll verify this and if I'm right I'll post a confirmation, but I'm 99% certain I got it now. Nothing to do with vacuum system after all.

 

[JeepJeepster]

The 05+ Libertys do use the A/C on the floor position, which IMHO is insane, so that could very well be happening.