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Join Date: Jan 2009
Posts: 6

Jeep heater problem

01/03/2009 3:12 PM

have a heater that show no problem with temp on the auto gauge. But heat from cord is low. Temp when on inside air works beat, and if using outside air you freeze.

Any ideas as to what to look for would help.

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Join Date: Oct 2008
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#1

Re: Jeep heater problem

01/03/2009 3:54 PM

sounds like your heater core is clogged....I's a real big job the dash has to come out. here is a neat trick take the hoses off the core and reverse them and drive it for a day or two...if you are still getting heat the core is only partially clogged and that should take care of the problem after driving ....If you get your heat back flush the system and put the hoses back or leave them it doesn't matter just flush the system or the core will just clog up again.

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#4
In reply to #1

Re: Jeep heater problem

01/04/2009 3:54 AM

Mr.wrenches Most heater cores have different size inlet & outlet tubes for a good reason, this prevents all but the most persistent from making the mistake of plumbing incorrectly. It does make a big difference. If the core needs to be flushed it would be best to do it with a garden hose so as to have a visual of what's going on. There is a good posibility the vehicle is equiped with a diveter valve that prevents hot water from flowing through the core during the warmer parts of the year when the presents of the heat in the core would not be desireable. These valves when they fail can greatly reduce or even prevent the flow of water through the core. I would suggest checking the heated water diverter valve for correct operation first and then checking the flow through the core with the garden hose and then check the internal flaps or doors that redirect the airflow for correct operation. These are normally operated by vacuum and the material used to make these tend to crumble away after a number of years causing the heater controls to partially or completly stop working. J.Conway

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#10
In reply to #4

Re: Jeep heater problem

01/04/2009 11:13 AM

Thank you for your information I have looked at the cord and do not see a diverter valve in the circuit. The core looks much like the core to my CJ5 if there is a valve it would have to be internal and unseen. Would that be the case if you have had more experiences with heater cords than I.

Thank you for your help.

KC

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#14
In reply to #10

Re: Jeep heater problem

01/04/2009 3:18 PM

KC, Thanks for your speedy replies to all of the post. Way to many people ask for help with a problem and fail to follow up with additional info or replies to post. There should be a GP award for Good Post when someone follows up as well as you have. I wish you well in finding a soulution to your problem. J.Conway

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#17
In reply to #4

Re: Jeep heater problem

01/05/2009 8:36 AM

Mr.Conway you are correct most cores have different size lines and a valve however 90% of jeeps do not and i would not recommend anyone to flush out their cooling system in their driveway with a garden hose the EPA would not find that very nice(I have had a few nasty neighbors) although that's what i would do anyway.funny though only one of us said to check the coolant level and that's what i would do first without even thinking.

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#8
In reply to #1

Re: Jeep heater problem

01/04/2009 10:21 AM

Thank you for your help I have now some new ideas in ways to fix this problem or look for other areas I did not think of. thanks again. KC

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#2

Re: Jeep heater problem

01/03/2009 11:45 PM

alot of possibilities here. But lets take a shot that it is a Jeep that is no more than 7 years old. You have a vacume line off or leaking and the swing damper that isolates the inside and outside air is not going full stroke.

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#9
In reply to #2

Re: Jeep heater problem

01/04/2009 11:05 AM

Thank you I did consider this, but found that we can get better heat from the change from outside heat to inside heat. This does not mean that the damper door is opening or closing all the way.

This may still be the case so I will look for this too.

again thank you for your advice.

KC

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#18
In reply to #9

Re: Jeep heater problem

01/05/2009 5:01 PM

KC gave you the best answer, in my opinion,

Thery...heater can raise pass through air 25 degrees.........

recirculated air starts at SAY 40 degrees...................results 90 degrees.

Outside air 10 degrees .... pass through adds 50 = 60 degrees.

Outside air will not get warmer until next spring.

Assumes all systems flow as intended and engine warms up normal

AND YOU ARE IN THE NORTHERN HEMISPHERE

MR. GUY

Thank you I did consider this, but found that we can get better heat from the change from outside heat to inside heat. This does not mean that the damper door is opening or closing all the way.

This may still be the case so I will look for this too.

again thank you for your advice.

KC

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#3

Re: Jeep heater problem

01/04/2009 1:19 AM

check in and out hoses from heater.

if both are hot, you have an airflow problem

if the out (return) hose is cold, it is a water flow problem.

then remove both hoses to heater core, and run water from a garden hose through the core, alternating the flow direction.

if the core was restricted, change the antifreeze, when you have it flowing properly.

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#11
In reply to #3

Re: Jeep heater problem

01/04/2009 11:21 AM

Thank you for the response to this problem. I took the time to check temps on the hoses this morning and found that they seem to be the same, though the pressure on the input seems stronger that the output. This I checked by the tightness of the hoses. This leaves me with the idea that there maybe a restriction in the core.

Thank you for your information.

KC

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Anonymous Poster
#19
In reply to #3

Re: Jeep heater problem

10/30/2010 7:22 PM

You are right on. If one hose is hot and the other is cold you have a plugged core, back flush should do it.

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#5

Re: Jeep heater problem

01/04/2009 6:25 AM

As you didn't give year the heater either has a vacuum operated blend door or an electrical operated blend door. Check vacuum supply to the blend door operator or electrical power.

Make sure both heater hoses are hot when the thermostat is open on the car. As a plugged heater core will also cause this problem.

Older vehicles had a valve in the heater hose to control flow look for this also.

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#12
In reply to #5

Re: Jeep heater problem

01/04/2009 11:35 AM

Thank you for your advice, I have thought that this might be the case. Your input helps me know that I am on the right track. I do believe it is vacuum, for it is a 2002, Grand Cherokee Laredo 6 cylinder. With out temperatures in the 20Ty's the fan rarely comes on, and the engine temp is just below 210 degrees F. I am falling more to a plugged heater core as I continue to check it out.

Thank you for your help.

KC

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#6

Re: Jeep heater problem

01/04/2009 9:06 AM

Greetings.

Possible air flow addition.

Had 1970 GMC pickup with low heater output when I needed heat.

Usually this happens in late fall when the weather starts turning cold.

Critter had crawled into heater inlet and made a nest of leaves and twigs. I had to take major part of heater in engine compartment apart to find this.

Have a Saturn that had engine inlet problem. Seems mice love to use fiberglass insulation and packed the area right below the air filter which then plugged air filter.

If this is your problem make screen of small grid hardware cloth over inlets and the critters (usually mice, chipmunks, or small squirrels) can't get in.

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Anonymous Poster
#7

Re: Jeep heater problem

01/04/2009 10:11 AM

I have a 98 Jeep Wrangler Sport. I have had a similar problem in the summer with heat coming out instead of AC. I did some investigating and found the AC system to be fully charged and functioning as it should. The problem I found was the little plastic doors inside the AC / heat plenum were not functioning correctly. It turns out that the heater core has full flow from the engine at all times. There is not a control valve in the heater system that restricts flow but rather plastic doors that change the flow of air into and out of the cabin. Being as these doors are such a pain to access I thought I would bypass the heater core all together by disconnecting the hoses and running the engine coolant right back into the engine. It worked well until I found myself in city stop and go traffic with the AC on. The engine started to overheat! I shut off the AC but it still ran way too hot. It turns out that the heat dissapation through the heater core in summer is needed to cool the engine correctly. I had to fix the little plastic doors after all. Hope this helps.

Bill B

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Anonymous Poster
#13

Re: Jeep heater problem

01/04/2009 11:50 AM

check to see if you have some air in the heater core that was my problum every time cooling system was work on the same problum came back had to drain air every time

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Anonymous Poster
#15

Re: Jeep heater problem

01/05/2009 4:19 AM

Most common cause of low heat output is low coolant level in radiator. This is the first check.

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#16

Re: Jeep heater problem

01/05/2009 8:04 AM

Check this one too....I had a 82 CJ7 that had a similar issue. It ended up that the heater hose coming from the pump was clogged at the pump, just barely some coolant getting through. I was able to pull the hose off, ream out the pump outlet tube, flush the system and WOW!! HEAT!! Its worth a shot anyway!! Happy New Year.

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Users who posted comments:

Anonymous Poster (4); Jerrell Conway (2); KC Comstock (5); mastrsmth (1); miketheboilerguy (1); Mr. Guy (1); mr.wrenches (2); OlympiaWA (1); rhandwor (1); Yosemit3 (1)

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