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96 Cherokee sport, AC works, fan on but no air out

1K views 24 replies 5 participants last post by  getterdun 
#1 ·
96 Cherokee sport, AC works, fan on but no air out

AC works, fan on but no air out, I can hear the fan, some air blowing out bottom after some time it will suddenly start blowing air out the front panels working normal

what is causing this delay?

some time it’s 20 to 30 min of driving in 109 deg before the air will flow out of front panels... AC gas pressure is good, compressor on ok. fan on but air blows out bottom not front until suddenly starts to flow out of all front panels...
 
#3 ·
Thanks for helping, very much appreciated.

the air flow does change, in normal AC pos, the air flow is out the windshield vent,(instead of normal front) ---
in by-level the windshield vent air goes off, the air is now going out the floor (bottom) vent, with some, very little, out the front panels, it will stay that way until it suddenly works normal, full air out front.... after 20/30 min of driving..

I can check, with gauge, the vacuum level soon. Not clear where the vacuum hoses are that control these vent outlets.... 103 deg now in shade...
 
#5 ·
My vacuum check... (corrected vacuum #'s)
AC OFF
at idle 14
with slight throttle bounce to 11.5 then to 16 then back to 14
throttle increase rpm up slightly to 16-17 holds steady

with AC ON MAX OR NORMAL
vac drops to 12
hold steady throttle vac goes to 13.8 holds ...

so.........
WITH AC OFF idle at 14 increase rpm vac AT 16

AC ON idle vac drops to 11.5 with increase rpm vac AT 13.8 steady

still think its a vacuum problem????
ok i’ll look for the hose
 
#8 ·
I would find the vacuum line coming off the intake manifold and trace it to hopefully find a connection that is loose, or a hose that is allowing vacuum to escape. Not sure if your Cherokee has the vacuum cannister behind right front bumper, but if so that's something else to check. I don't think doing a vacuum test straight off the intake manifold would tell you if a vacuum line is leaking.
 
#9 ·
96 cherokee sport ac problem

Thanks getterdum
I also tested the main ac vacuum line by installing a 3 way connector to my vac gauge and I did get good vac psi at 13 (corrected) and went up slightly as I rev engine.

My first test was to check the whole vac line at the junction where the line goes into the fire wall to the cluster switches...( I disconnected that line ) the vac was good and remained high after engine was shut off.

When I included the line into the firewall to the gauges the vac was also good but it did drop slowly after the engine was shut off.

I had to take a few kittens to vet and the ac did work ..
very temperamental.. works ok then stops only air out the bottom then it will work normal with strong air out front...

Can this be a slight leak at the sw/ manifold??
Not sure what that is or how it works...
Maybe time to remove front dash panel and get to the switches??
Any help out there on best way to remove front panels and work on the ac vac line and switches??
** 96 Cherokee sport **
 
#11 ·
Corrected vac gauge readings

CORRECTED VAC GAUGE READINGS
vacuum 12 to 14

You are correct.. I was reading the gauge incorrectly.. the actual vacuum is 12
Measured at the junction of the vacuum lines (to heater- a/c controls -- your vacuum supply diag)
rev engine slightly goes up to 14 plus.

Engine off, slowly returns to zero.

Intake manifold vac is same at 12

Is this within the normal range for correct vacuum???
 
#12 ·
Corrected vac gauge readings

CORRECTED VAC GAUGE READINGS
vacuum 12 to 14

You are correct.. I was reading the gauge incorrectly.. the actual vacuum is 12
Measured at the junction of the vacuum lines (to heater- a/c controls -- your vacuum supply diag)

rev engine slightly goes up to 14 plus.

Engine off, slowly returns to zero.

Intake manifold is same at 12

Is this within the normal range for correct vacuum???
 
#13 ·
CORRECTED VAC GAUGE READINGS
vacuum 12 to 14

You are correct.. I was reading the gauge incorrectly.. the actual vacuum is 12
Measured at the junction of the vacuum lines (to heater- a/c controls -- your vacuum supply diag)

rev engine slightly goes up to 14 plus.

Engine off, slowly returns to zero.

Intake manifold is same at 12

Is this within the normal range for correct vacuum???
Pretty much.

I wonder if your exhaust is restricted. How does it run? Strong?
 
#14 ·
Runs very well. Excellent dependable vehicle so far..
This is baffling to me..
AC is cold.
Blower fan strong except it blows out the bottom...
Then it will decide to flip into normal and blow out the front vents..
Once it begins to work normal it will continue to do so..
its just when you start up it takes a long time to switch from blowing out the bottom to normal operation... It has always started blowing out the front vents when ac was initially turned on.

I just checked the R134 refrigerant pressure and it is at 30 on my gauge ..a little low ..
At 103 deg outside temp I should be getting around 50 psi
I am getting nice cold air 44 deg except all the air is blowing down thru floor vents

idle vacuum I read 14 in hg . 17 at 1500 rpm looks ok to me????
Too low?
What controls the fan air ducts?
Is this the default state?
Is there a way to manually control the duct to make it blow air out the front?
 
#15 ·
If when you first start up your vehicle and the vents are blowing out the defrost and only after a bit of idling do they switch to the front vents indicates a very slight vacuum leak. More than likely its your Vacuum check valve leaking, it should be connected to the vacuum hose that runs to your intake.

Default no vacuum the vents it usually blow out of the defrost.

You said that once you turn the engine off that it looses vacuum, how fast does that happen? For reference my Jeep had been parked for 30 minutes when I disconnected my glass spaghetti jar vacuum canister to install a new proper vacuum canister and it had substantial vacuum left.

You in the sunny (currently humid) City of Tucson AZ? Welcome!!!

Edit:

Circled in red is your one way check valve. Either test it by pulling a vacuum on it, or replace it.
Electrical wiring Cable Automotive tire Gas Auto part
 
#16 ·
One way valve tests good

The Air has only blown out the bottom vents. Never out the defrost vent.

Where you circled on the one way check valve is where I tested the vacuum.
I pulled the hose going to the firewall off of the one way valve and placed a three way connecter so that the vac line was still connected to the system vacuum and tested vacuum.
The vacuum did fall to zero slowly, it want to zero in about 30 seconds.

Again..
to be clear.
When I tested the Vac WITHOUT the vac line going to the firewall it held rock solid.

The decay of vac was only noted when I connected my vac gauge to the one way valve AND to the vac hose that goes thru the fire wall.
I hope that's clear.

I tested the one way valve and it tested very good.

I drove yesterday very humid, hot day transporting 3 kittens and puppy to vet for foster homes.
Three hours of driving and the air only blows out the BOTTOM VENTS now.
 
#17 ·
So you only have a vacuum leak when you include the vacuum lines that go through the firewall.

At that point I would check your vacuum connection to the controls and if that looks good I would test the AC controls (make sure they hold vacuum).
 
#19 ·
"fan on but no air out, I can hear the fan, some air blowing out bottom after some time it will suddenly start blowing air out the front panels working normal"

Suddenly is the word that got my attention on re-reading your post. It seems likely that the blend door is obstructed, and slowly the vacuum keeps pulling it until finally it snaps into the right position. I would try to figure out how to access the blend door to check for obstructions. I wonder if blowing compressed air through the vents might work?
 
#20 ·
gutterdum

The last few days the air blows out the floor vent all the time now...
Blend door obstructed.... sounds like a good solution.
Is there a way to get to the blend door without removing dash panel?
Can I get to the blend door control wire? from the AC control module locating?

I did find instructions on getting to the AC Control panel.
JEEP CHEROKEE XJ HEATER CORE REMOVAL PART 2
 
#21 ·
Wish I had experience with your particular situation, but I don't. I have pulled the dash on one vehicle; and I don't want to ever do it again. Took way too long to do, and had too many issues. Me, at this point, I'd just live with it and hope that eventually the door will work its way free again.
 
#24 ·
Yeah, I saw a lot of stuff for 97 and up but not for the 96. Does what you see look anything like the videos on utube? I'm going to do some more looking for you. A picture of what you see when you look up at the motor control might trigger some additional help.
 
#25 ·
Well I looked but could find nothing helpful regarding your 1996 Cherokee Sport. I couldn't even find a part for it on the OEM sites. If it really bothered me I would take my leaf blower and blow through all the vents hoping to dislodge any obstruction. Not the best way, but that's what I'd try.
 
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