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My heater blower puts out more air when not running, here's why

110K views 107 replies 56 participants last post by  93YJ4FUN 
#1 ·
I've read about guys with jeeps that bake them out after a couple minutes and was jealous because mine didn't. My heater blower wasn't putting out any air hardly at all while the YJ was running. However, if I just put the key in and turned it without starting it, it blows very hard.

I used the search feature and couldn't find anything that covered this.

After checking voltages and other things, I pulled my hood vent cover off. It was spotless and had zero debris inside. I noticed that the vent intake door was open. When I started the jeep up it closed with the heater control on defrost/heat/vent. When I shut it off the door re-opened. Both intake vent doors are controlled by the vacuum switch attached to the heater controls. It has three ports and two vacuum tubes connected to it.

It turns out my tubes had been plugged into the wrong ports! So when the jeep was off the intake doors were open and when running the vacuum closed the doors so no air was coming in from the hood vent.

As the proud owner of jeep that no longer requires a hooded sweatswirt to stay warm in, I hope this post might help somebody else out.
 
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#53 ·
tony673 said:
OMG, I think I have the same problem. I guess I know where I'm spending my day off tomorrow.....under the dash of the YJ!!

I've had a draft that just won't quit ever since I replaced the body tub. I've tried everything!; duct tape, masking tape, electrical tape, spray in foam insulation, cloth-you name it. Still, my legs feel a breeze.

Maybe I messed up the tubing placement on that vacuum thingy you speak of.
I can sympathize - my Jeep had, for some reason, a draft coming in around my ankles all winter. The heat comes in strong, so I really didn't have much to complain about - however my passengers were feeling the worst of it.
Turns out there was a nice big vent on the right side under the dash, around ankle height, that seemed to go straight to the outside air.
:confused:
I could see no reason for there to be a passive cold-air vent in an already chilly vehicle (I say 'passive' because there appeared to be no motors or airflow when idling, the air was forced in at highway speeds) and so I taped it up with some good ol' Duct Tape and paid close attention to the Jeep for a few weeks afterward. I noticed no change, so I guess there was a useless air vent just... chilling out...

I do not profess to be a car-guy, I'm seriously 85% retarded when it comes to vehicles. However, the thing appeared to be useless and served no purpose that was missed once I taped it up. And the Jeep is several times warmer!
:2thumbsup:
 
#56 ·
So, I have read through this post, can anyone explain to me this: I have the a/c in my 95. When I have the heat on, it only comes through the defrost and the floor vent, none of the settings enable the heat to come out of the vents under the radio, that is where the a/c comes out when turned on....is there a way to get the heat to come out of those vents? I regularlly drive with the doors off; however, lately I have been freezing my bottom off....
 
#58 ·
dlnagold -
Someone jump in if I'm wrong, but your AC system is a packaged unit under there that is totally independent of the heater/defroster system in terms of both controls and ducting. In other words, you could run your heater and AC at the same time. I've heard that the AC systems were dealer-installed options--whether that's true or not I don't know, but it is definitely stand-alone. Nothing wrong with your system based on what you described.
 
#61 ·
Very nice job! Wish i would've read this before I 'trail fixed' mine.
One of the doors was rusty so it broke the little plastic doo-hickeys (that's a technical term) and I have it set to blow a lil heat and a lil defrost all the time...but I bet my pass side door isn't opening...I'll look in the AM if wifey lets me play Jeep :)
 
#62 ·
This is an AWESOME thread!!! I have the same problem with the cold air coming down by my legs. I can't seem to track it down how it's getting into the cab. I'll look more into to it this weekend.

What if my blower is running nonstop (at all times no matter what the setting) ???

There was a 4.0L installed before I bought it, and I hope Mr. Handy didn't screw up the wiring! :(
Does anybody know what I should look for?
 
#63 ·
I'm gonna flog this dead horse..........

What happens if all the cables, vac lines, vent doors all operate as they should and you STILL have cold air coming in? Is it possible that the drivers side vent door is opening when I'm rolling down the road? That's where the air is coming from. In my driveway tests it is closed when it should be.
 
#64 ·
is it coming out of the vents? if not it could just be a gap in the soft top near where the door closes. Does cold air blow in even if the heat is turned off? If not and it's only cold when the blower is blowing then you might need a new water pump or maybe just a new fan belt becuase it could just not have the coolant moving, but you would already have an over heating issues i would think if that was the case.

As with my jeep i get cold air blowing in at idle with the heat on but once it reaches 1500 rpm i get heat, i'm hoping its not the water pump and maybe just the belt.
 
#66 ·
mine started doing the same thing when i did what this thread said and turned the way the vacume valve was pointing. I didnt bother me because it would just leave the heat on low all the time. As for the fix i would say it probably is one of the air intake vents staying open all the time. Try puting a fan over the cowl and see if you can feel the air comming through the vents.
 
#67 ·
My heater blows air that's just slightly warmer than the air outside and doesn't "roast" me out at all :(

I have no idea what could be wrong with it, I've checked almost everything.

As for the air vent being open, it is and it won't close all the way. I can't figure out how to tighten the wire either for the life of me. I guess I'll just duct tape it up during winter and re-open it in the spring.:D
 
#68 ·
Anyone have any suggestions for this situation? My heater has always worked well - until last week. It seems that my heater would not shut off no matter what position I had the controls in. At one point I thought I had at least figured out how to get it to cooperate - not that it was working as it should but at least stopping the heat. Then yesterday I was cruising along and I thought my feet were on fire. I noticed that my heater decided to starting blowing again, no matter what I tried. Finally as I continued down the road it shut off and stayed off for the remainder of my trip. Does this sound like a vacuum hose problem or something else you guys can suggest?

Thanks
 
#69 ·
ok... my heat has never "roasted" me out of anything.. it really isn't that cold but my girlfriend always put a blanket on her lap everytime she's in it. day or night in the winter.. we even have a designated jeep blanket just for her... all my flaps work. had a bad heater core a few weeks ago and replaced it and took the time to check all flapper doors and cable operations.. all my vac lines are solid and have been checked... and my heat is still horrid.. it has decent air flow but never gets above just warm air..

my temp gauge is always steady at about 200 to 210 so you think my little YJ would have plenty of hot air..

any idea..

maybe Chrysler just dropped the ball on it..
 
#107 ·
ok... my heat has never "roasted" me out of anything.. it really isn't that cold but my girlfriend always put a blanket on her lap everytime she's in it. day or night in the winter.. we even have a designated jeep blanket just for her... all my flaps work. had a bad heater core a few weeks ago and replaced it and took the time to check all flapper doors and cable operations.. all my vac lines are solid and have been checked... and my heat is still horrid.. it has decent air flow but never gets above just warm air..

my temp gauge is always steady at about 200 to 210 so you think my little YJ would have plenty of hot air..

any idea..

maybe Chrysler just dropped the ball on it..
Without going into too much detail, what’s involved in replacing the heater core ?
 
#70 ·
I cant see anyone's pics?

So what would happen is no vacuum were connected at all? Cause now that I think about it, I didnt connect my vacuum line to the heater, and havent had a problem. It stays some what nice and warm.
 
#72 ·
#76 ·
read all of this and more. but here is my question. What closes the pas.side vent door? when I move the lever from vent back to heat/defrost it just lays there, open..... mocking me.
It moves easy enough. But I have to reach in there and hook the arm with my finger and close it. Idont think that that is how the factory made it.
any help is appreciated.
 
#78 ·
Hey guys, hoping someone can tell me if this is feasible or not. My Jeep has been cold and I found this thread. Anyway, I found the vacuum source on the back of the manifold near the firewall on my engine. after tracing the vacuum hoses, I found mine is running under the Jeep. The vacuum motor switch on the heater control was also hanging. I have it hooked up and adjusted(only the green vacuum hose is connected), but I need to pick up a check valve, some vacuum hose, and fittings to fit it this weekend. I am thinking about using the ported vacuum on my CTO valve to apply the vacuum since the only thing hooked up on the CTO is the large ported vacuum and EGR. My question, will this provide enough vacuum to actuate the air door or not? Or should I use the manifold vacuum and T into it? I think the manifold vacuum may have been used to run the 4WD vacuum on the front axle, not totally sure. The pic below with has the port I am thinking about hooking up circled in red. Thanks in advance!

 
#80 ·
Hey guys, hoping someone can tell me if this is feasible or not. My Jeep has been cold and I found this thread. Anyway, I found the vacuum source on the back of the manifold near the firewall on my engine. after tracing the vacuum hoses, I found mine is running under the Jeep. The vacuum motor switch on the heater control was also hanging. I have it hooked up and adjusted(only the green vacuum hose is connected), but I need to pick up a check valve, some vacuum hose, and fittings to fit it this weekend. I am thinking about using the ported vacuum on my CTO valve to apply the vacuum since the only thing hooked up on the CTO is the large ported vacuum and EGR. My question, will this provide enough vacuum to actuate the air door or not? Or should I use the manifold vacuum and T into it? I think the manifold vacuum may have been used to run the 4WD vacuum on the front axle, not totally sure. The pic below with has the port I am thinking about hooking up circled in red. Thanks in advance!

 
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