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New Member - 98 with defrost only

Scott26

NAXJA Forum User
Location
Columbus Indiana
Just got my first XJ 98 with 135K miles. I have been using the search to research why I only have defrost only. I DO have functioning cruise control and have visually inspected the line that runs under the battery box and do not see any cracks etc. Since the cruise works is this an indicator that helps narrow the diagnosis? Any advise would be appreciated.

I hope to get some pictures posted. With the help of a friend and forum member I am replacing many parts to get my almost stock(factory wheels rusted out) XJ ready for several more years of fun.

Thinking of replacing the check valve then maybe running new vacuum lines?
 
Some XJ's have an HVAC check valve, others just have a tee (see pics).

Check for a broken HVAC vacuum tube going in to the firewall. See pics.

jpgHVACCheckValve.jpg


Broken tube and fix:

HVACTubeBroken.jpg


HVACTubeFix.jpg
 
Thank you for the pictures. Mine has the T at the firewall and the line appears good going through the firewall. The only check valve I see is back at the elbow that connects to the intake, but I am assuming if the cruise works I am not loosing vacuum there?
 
there's a vacuum harness behind the HVAC control unit.

if someone was rough pulling it out they may be broken.
 
OP,

Do you feel any airflow from any other vents when they are selected - even a tiny bit?

Here's a chart that shows the vacuum routing for the various mode selections. Note that when Defrost is selected all vacuum is removed from the actuator. If Defrost is not selected and the Defrost door is driven open (spring loaded actuator) the actuator may be bad, the Defrost door bell crank may be broken and the door remained open when it broke, or the vacuum control tube to the actuator is broken. Note also there is a MIX setting where the floor door is open and the Defrost door is driven part way. If you select MIX (selection #6) and you feel air coming out of the floor vents, as well as the defrost vents, then the actuator is working (partially anyway).

jpgModeSelectFunctions.jpg


Here's a pic showing the Defrost actuator and the bell crank. The Yellow tube is full Defrost and the Blue tube is Mix (mid position).

IMG_20110418_094751.jpg


You can see the Defrost door actuator bell crank by removing the trim panel and knee blocker from under the steering column and looking up past connector C201. Select Defrost and Mix with the mode selector and watch the movement of the actuator and bell crank. See pic.

Defrost%20Door%20Troubleshooting.jpg

.
 
Thank you very much for the detailed information. There is not air coming out of any of the vents except defrost but I will check them all again to be certain.

I appreciate this very much and will likely dig into this weekend and see what I can find out.

Regards
Scott
 
Today after checking the HVAC unit everything looked good and I went over the vacuum lines and found a small break in the line that I have overlooked previously. Repaired that section of the line and everything worked great. THANKS TO EVERYONE FOR THE ADVISE AND PICTURES.

New radiator, thermostat, water pump, and hoses are next job. Water pump is making little noise and there is a very small radiator leak. Brakes, shocks, rear springs, motor and transmission mount are done.
 
Sidewinder:
THIS IS GREAT! Just what I need to work on son's 01.
After engine swap there's no HEAT but blower works fine. I mean, mixture door actuator
or ____ isn't working like It used to. (01 cherokee 4x4/auto)

BUT, how 'easy' is it to get to while dash is IN?
I'm kinda busted up @ 54 and it's hard to get under there, and then see with my 'readers' on.

Did you ever think to make a STICKY about this?
In my searching, it looks like there are quite a few vids on Youtube about flapper door 'fixes' and such.

Thank you for offering this to everybody.
Errol
 
Sidewinder CC:

Thanks for the great write up and pictures. One of my 2000's only had defrost and instrument panel, nothing to the floor. The blend door was previously stuck due to a pinhole in the heater core leaking antifreeze, I expected the floor door to be stuck for the same reason. After disassembling the lower dash I was able to operate the floor door manually and feel the back of the actuator - no vacuum hose connected. I was able to find and reconnect the hose and am back in business.

Thanks again!
 
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