Another 99XJ with lukewarm heat.

Hi all,
I picked up a clean 99 XJ for my Daughter last winter and all was well until recently when it started blowing Luke warm heat only.
I will try to be very specific to rule out any unnecessary speculation.
Her temp gauge was registering fine at the 200deg area.
The heater core hoses both felt pretty warm when engine warmed up.
I replaced her thermostst with the 195 deg "better one" the auto parts store guy recommended which was the (fail safe) one.
After I did that nothing changed with her heat other than the temp gauge sits a bit cooler religiously at 195deg.
I decided to back flush the heater core with a garden hose and I got some nasty brown water out of it and it pretty much cleared up right away and flow was good.
I decided to flush the radiator as well and refilled the whole thing with prestone 50/50 mix.
I ran the system, burped the air.....took a while as the lower hose collapsed on itself during the process but corrected itself once I burped the air out.
I let it warm up and cool several times until I was satisfied that the resevoir no longer needed topped off.
My daughter has since taken several trips on the highway to and from college with it with still Luke warm heat only.
Both heater core hoses are hot when engine is hot so my best guess is something in the dash, possibly a blend door.
I know the later models like mine do not have a heater control valve but I have heard about blend door problems.
I don't know what I'm looking at but I do have a Hanes manual I need to look through to try to locate my blend door and get a grasp on my hvac system.
Just to note that the air volume and movement seems to be working fine and routing through all the proper vents on command, just Luke warm heat.

The only thing that struck me kind of weird is that a couple times when I initially warmed up the vehicle I noticed the vents seemed to blow pretty warm air, almost hot until the vehicle warmed up further then it backed off to Luke warm after a short test drive and would not change from that point forward, even while idling several minutes.

I'm thinking I have some sort of crappy vaccum actuated flap I need to locate and check.

Any thoughts for this 99 XJ, 4.0 auto, 4WD are greatly appreciated.

Check the to make sure it is staying in the vent/floor position and not defaulting to the defroster. If the line to the vac ball behind the front passenger bumper cap is broken it will have great heat from the vents at idle but will default to defroster under a load.

Vents all blow lukewarm and change with the settings like they should.

It just felt a bit hotter once before engine got really hot from test drive then blew lukewarm again.during drive and idling afterwards.

Seems like it wants to blow heat but fizzles out.

I have the SAME problem. I just replaced my heater core.

I suspect the problem is that I have some air in the coolant system. That... or a clogged radiator.

I got the same thing going on. The only thing that I can figure is, if there is any type of foam seal around the blend door that could be deteriorated ? All positioning of blend door is operating and you can hear it move when operating the heater control. This is also on a 99 XJ Sport.

I had the same thing. There is a mod to the thermostat housing you can do to help bleed the trapped air to get the hot your after.

I just did the flush kit and burped it that way. Took all of 15 min start to finish and had great heat after.

http://www.lunghd.com/Tech_Articles/Cooling/BurpAirMod.htm

Or... just use a Mopar Thermostat, which has a burping mechanism built into it. Then just burp it yourself.

thatxjguy said:

Or... just use a Mopar Thermostat, which has a burping mechanism built into it. Then just burp it yourself.

Click to expand...

What is the procedure to 'burp it yourself'? I just bought a mopar t-stat.

Taggdog said:

I got the same thing going on. The only thing that I can figure is, if there is any type of foam seal around the blend door that could be deteriorated ? All positioning of blend door is operating and you can hear it move when operating the heater control. This is also on a 99 XJ Sport.

Click to expand...

I'm thinking this too.
Looks like I need to cut my plenum and look at my blend door flap.

has anyone here used to heater greater blend door flap upgrade kit?

It's worth the money to me so my daughter can have heat and a clear windshield in the winter.......she has lukewarm heat so it does help defrost but by the way the heater hoses both feel hot this thing should be blasting super heat like my XJ does.

http://www.rockauto.com/info/RB/902-326_IS.PDF

This is all the I fo I need.
Excellent pics to walk me through this.

Man, will someone please call heater treater and tell,those guys to make a better video?.....good night....what a train wreck that video is.

Please let me know what the result is. Thanks.

I will definitely post any updates.
My daughter said it was fairly warm tonight on her way home but not hot.

I remember when I first turned her vents on to check the blower function after we bought the jeep for her this black, sorta rough textured foam chunks blew out of her vents.

She also had a terrible vibration when her blower was running on high so I removed it and found a dead rodent that got buzzed by the fan and was like a hairy potato chip and I didnt want her breathing air from that fan as it did have a nasty smell.


I replaced her blower motor since I had already bought one but I had to trim the tips of the fan blades because they rubbed ever so slightly as they were slightly different than the original.

Anyways....I'm wondering if those black foam particles were from her deteriorated blend door seal.......hmmm but hopefully I will have time this weekend to at least check it out.

Sounds like heater core is failing. My heat blows really hot. Can't keep my hand over the vent.

Below is a schematic of the '99 - '01 Blend-Air Door circuit.

You can check the actuator operatiopn by positioning yourself in the passenger footwell and looking up to the left corner of the bottom of the HVAC Unit.

Turn the ignition switch to RUN and move the Temp Selector knob from stop to stop. You should be able to see the actuator turn slowly from stop to stop (about 90 degrees travel). If it doesn't move, remove the motor/actuator and leave the electrical connector plugged in. Try it again. If it won't move the motor is probably shot, if it does move see if you can turn the Blend-Air Door extension with your fingers, if not, try with pliers. If it won't move the door is stuck.

Yep, I checked that all out this morning.

I set the temp control to middle setting then removed the blend door motor from under the dash.
I used the plastic intermediate piece that connect the motor and the flap to turn the flap by hand and it felt like it moved freely full range with no binding.

Then with the motor still plugged in I moved the temp dial cold to hot a few times and watched the motor turn stop to stop.
I then set the temp dial full warm, turned the flap full closed as it would be in full hot mode then reattached the motor.
For some reason I may have resynched the motor because it was blowing pretty warm but not really hot so it took it for a test drive and it started blowing pretty darn hot while driving but still not as hot as my 99 XJ but much, much better than it was before.
Oh I also took the motor apart to inspect it and everything looked solid.

One thing I noticed is that it seemed to not blow as warm after switching from defrost to dash vents when I returned from my test drive and checked it while idling hot.
Both of my heater hoses were piping hot as well as my upper and lower rad hoses.

I ran out of time to mess with it but it seems to blow warmer if i leave it on dash vents than it does defrost unless it's just my mind playing tricks on me.

Anyways it seems to be blowing pretty warm to me so I will continue to get progress reports from my daughter.