No heat

[03kjjeep]

Hey guys im really struggling to find out why my jeep wont blow hot air.


Its a 2003 jeep liberty with the 3.7 and it had a new heater core installed last year and just had head gaskets and water pump, thermostat, rad cap, and radiator hoses and clamps done this week. The cooling system was completely flushed and topped up with the correct fluid. The system has been burped repeatedly so I don't think its an air bubble. It pressurizes once at operating temp and does not over heat.



While driving or at operating temp it will blow hot then gradually cool off until it blows just cold air. If I turn off the blower and wait a couple minutes then turn it back on it'll blow hot again for a short amount of time.



Ive checked the temp of the heater core lines coming out of the fire wall and there is only a 10 degree difference maximum.


I have no idea what to look for and no clue why its doing this. I've replaced the resistor for the different blower power levels and those are now all functioning.




Thank you guys in advance!

 

[JBDive]

I think you are in the same boat I am although everyone keeps saying heater core. I think the flapper or whatever you want to call it for selecting how much outside air is being allowed inside is not setting correctly even thought I can hear things move in the dash. Mine has always allowed to much outside air in as even in AC/recirculating you can smell outside smells.

I've thought about taking the venting off inside the hood and just manually restricting the amount of outside air that can come into the cab by cutting a piece of plastic or rubber to restrict the vent size.

Things to check:

Clean the vent behind the glove box, it's there, use a vacuum.
Pull the heater houses and back flush into a bucket so you can see if anything comes out.

 

[tommudd]

Heater core, no amount of flushing will get everything out if partially plugged
The way the heater core is made it will take a short cut and not flush out everything no matter what you do

You can try every trick there is, but...........

 

[LibertyTC]

With a new heater core it sounds like it may be...The flapper door, also better known as the blend door.
It is electronically controlled and can seize in a fixed position, if not electronically working correctly. Or maybe it needs some PB blaster to make it work again ha ha..
The modes, re-circulation, vent. floor etc are vacuum controlled.
One member apparently manged to get the door moving again by somehow fishing though one of the vents, to make it work again.
In worst case scenarios, you to remove the dash to repair the blend door, which is a big job !
I used the word "heat" in the KJ section search engine and there is good threads here:
Jeep Liberty Forum - JeepKJ Country - Search Results
It is also a good idea to read applicable FSM sections. Index of /manuals/Jeep/KJ
Hope this helps in some way..

 

[LibertyTC]

If I turn off the blower and wait a couple minutes then turn it back on it'll blow hot again for a short amount of time.

Now that I think about this ^.. you could have a vacuum leak.

 

[03kjjeep]

Awesome ill do some investigating and update you guys with what i find. I appreciate it!

 

[Jeff Ferguson]

My two cents on the "flushing won't work" theory...

My '04 Liberty had following symptom:
Barely preceptible heat when dial in red zone (min or max)

Other factors:
A/C works fine
Blower motor works all 4 speeds
Defrost to Floor vents all work fine
Temp gauge in middle, rock solid

What I did:
Inspected for loose vacuum lines, loose electrical plug-ins (found nothing)
Flushed heater core only by filling with Prestone flush (30 minutes)
Flushed and backed flushed with garden hose spray nozzle both inlet and outlet
What came out was not impressive, transparent pink/rust in color for 15 seconds than ran clear for next 5 minutes

Somehow, someway it fixed the problem, could cook marshmallows in the cabin now. What gives? Was sure it was blend door actuator or dial controller.
Grateful for this forum as i would not have given this idea the time of day but am thrilled it works!

 

[Big Al]

I'm going to try and back flush my heater core as see if it heats the cab better. Heats come out hot for a few minutes and then changes to cool.
If I leave it on setting one, I get more heat than if it's on setting 4