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Heater blowing warm (not hot) air

186K views 73 replies 37 participants last post by  pvansch1 
#1 ·
Bought a 2002 TJ Wrangler over the summer and love it. Issue is that it is blowing warm (not hot) air from the heater. I read hundreds of posts on this and think I have done/checked everything. Coolant level is fine. Temperature is running at 210 degrees. Both hoses going into the firewall are very hot to the touch. I removed both hoses and flushed the heater core both ways. Does not seem to be any obstructions as water flows freely both ways. Blend door actuator motor is working properly. Removed the actuator motor and manually turned the blend door. I can hear hear it move in both directions so that seems fine as well. Air Cond works fine. Its getting cold here in NJ so trying to fix this issue asap. Any advice? This is driving me crazy. Thanks.
 
#2 ·
Seems like you covered everything. Mine does not blow so hot either. If you figure it out please let us know.
 
#6 ·
Have you tried CLR?

I flushed my heater core and some gunk came out, and the heater is warmer now, but it still doesn't get as hot as I'd like.

I've been thinking about putting a little CLR in the heater core for a while then flush it out real good and see if it helps. I've heard some folks have had good results doing this.
 
#9 ·
Mine's the same way. Runs at 210, flushed the heater core and it flows freely and no junk comes out. Used CLR. Cooling system is clean. Blend door is not stuck. It just doesn't put out much heat. I'm thinking I'll have to replace the core eventually. For some reason it's not transferring heat from the coolant.
 
#10 ·
Something I found on ours when I had to replace it, the bottom half of the core was all plugged up on the outside. Dirt/debris had built up, coming in through the fresh air intake. When it got wet it turned to more or less mud and the blower had pushed it into the core fins, blocking any airflow on the bottom half.

Might be worth a shot to pull your blower motor and taking a look inside the housing.
 
#11 ·
Something I found on ours when I had to replace it, the bottom half of the core was all plugged up on the outside. Dirt/debris had built up, coming in through the fresh air intake. When it got wet it turned to more or less mud and the blower had pushed it into the core fins, blocking any airflow on the bottom half.

Might be worth a shot to pull your blower motor and taking a look inside the housing.

with all he has done , this sounds like it could be the problem.
i am saving this post.
 
#15 · (Edited)
A easy check to see if your heater core is stopped up with dirt on the outside and not letting the air flow thru it freely to transfer the heat to the ducts of the Jeep is to set it on defrost and temp on cold and feel how much air is flowing . Now switch it to Hot and see if it loses a lot of air flow( it will be a little less just because it has to blow thru the core but it should not be a lot less ) if so your core is clogged with dust and dirt and need cleaned .
The best way is to remove it but if you pull the blower motor and you have a air compressor and a nice long air gun you can sometimes blow it out.
Be careful and not bend the honeycomb closed.
 
#20 ·
I'll try the defroster test today but one bit of information I forgot to add in my original post was that I noticed if I have the fan set on the lowest setting there is decent hot air coming out of the vent. But the higher I turn the fan the cooler the air gets. Is that also symptomatic of a blocked/dirty core? Or an issue relating back to a clogged fresh air intake?

I'll break out the air compressor today and see if that makes any difference. I will repost later with results.

Love this forum. You guys are great.
 
#24 ·
Well, here's what I found when I pulled the blower motor:



Here's after I blew it out best I could:



I haven't put it back together yet and there are some other things I need to do before I can run the heater to see if it's improved, but I'm betting there's an improvement because a good 25% of the core wasn't allowing airflow through it. I'll post results later.
 
#26 ·
It now gets uncomfortable to hold your hand over the defrost vents. I wish I had a thermometer to check the air temp at the floor vents as per the FSM. I did grab one of the wife's candy thermometers and put it on top of the defrost vent and got 125 degrees. The ambient temp is 70 degrees. The specs are for the air temp at the floor vents with the engine at operating temperature to be 147 degrees. Without a proper thermometer, I won't be able to tell if it's within specs, but it's blowing pretty damned hot, so I'm happy. Now to see how it does in the cold :thumb:
 
#27 ·
s14sh3r...What year is your Jeep?

I was just wondering if you had to remove your blower motor from under the hood (behind the battery) or from inside the Jeep? I think they changed where you access the blower motor sometime around 01 or 02.

I think I may need to clean my heater core like you did and it looks like you had decent access to the heater core.
 
#31 ·
Mine's an early 97. It was easy to get out. I had to remove the battery and PCM and remove 3 bolts from the blower.

humpaco, I'd just have to look and see how the later model TJ's are set up. As it was, I could see part of the core. A small inspection mirror and a flashlight let me see all of it.
 
#28 · (Edited)
This preston flush kit works very well and cost only around 15 dollars.
And the preston radiator flush and cleaner chemical will remove an unbelievable
extra amount of rust and corrosion that a water back flush can not remove and it only cost 6 dollars.
I install these flush kits on all my Jeeps and do a back flush every 3 years.
The whole labor time to install kit and do a flush is 20 minutes.
If you do this and pull the blower motor and clean the outside of your heater core with compressed air you will have heat like when it was new.
 
#30 ·
scott howard said:
A easy check to see if your heater core is stopped up with dirt on the outside and not letting the air flow thru it freely to transfer the heat to the ducts of the Jeep is to set it on defrost and temp on cold and feel how much air is flowing . Now switch it to Hot and see if it loses a lot of air flow( it will be a little less just because it has to blow thru the core but it should not be a lot less ) if so your core is clogged with dust and dirt and need cleaned .
The best way is to remove it but if you pull the blower motor and you have a air compressor and a nice long air gun you can sometimes blow it out.
Be careful and not bend the honeycomb closed.
Scott, I get the same airflow through the top vent on hot and cold so it doesn't sound like a clogged/blocked core. (right?)

Also, I removed the blower motor to see if i could gain any kind of access to the core to blow it out with compressed air. I have a 2002 so it is removed from under the dash rather than under the hood behind the battery. Couldn't see or feel the core so couldn't really do too much.

I'm out of ideas at this point. Any other suggestions?
 
#32 ·
s14sh3r, I'll bet with all of that dust and gunk you got off your core that solves your problem. Great pics.

Still trying to figure out why my air gets cooler the higher I turn up the fan. With the fan off I get good hot air out of the vents.

I'll try the CLR this week. I think i covered all the other bases.
 
#36 ·
Heat at last, heat at last.

My issue was not that the core was blocked but rather that the blend door was leaking and not seating properly. To refresh my symptoms: I was getting hot air out of the vent with the fan off and on low but the higher I turned the blower motor, the cooler the air would get.

I bought the aftermarket door from Heater Treater. I didn't have the time to do it so I took it a local radiator shop recommended by the HT website. I am glad I did because it didn't fit perfectly and he had to modify a part a bit to make it fit. He showed me pictures and I would have struggled to do that. He also flushed the core with a combination of water and air. I think the air make a difference because the 3 times I flushed it with just water, I got nothing but clean, clear water out. He said before the flush he was getting 110 degrees out of the vents. After flush with air and water; 135 degrees.

Flush made a difference but my real issue was a not-properly seated blend door.
 
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