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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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#2 ·
Could you please post a picture or a diagram as to which tubes go to which port. All I know is that one is for the vacuum source on the intake manifold, one goes to the door, and the 3rd one is for A/C? Does that mean when you have A/C hooked up it is the one that _closes_ the door to recycle cool air?
Anyway, it would be cool to document this. It is not documented in the FSM or anywhere else as far as I can tell.
 
#3 ·
Yea someone how are these supposed to be hosed? Help a brother out!

Nitrox73 said:
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.
 
#5 ·
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.
 
#8 ·
ctm said:
Could you please post a picture or a diagram as to which tubes go to which port. All I know is that one is for the vacuum source on the intake manifold, one goes to the door, and the 3rd one is for A/C? Does that mean when you have A/C hooked up it is the one that _closes_ the door to recycle cool air?
Anyway, it would be cool to document this. It is not documented in the FSM or anywhere else as far as I can tell.
I agree, it would be helpful.:D
 
#9 ·
X7

Bump to the top

.... any ideas from anyone else where to find this???
 
#12 ·
doug_1994 said:
My heat allways roasts me out. If you want me to take a pic of mine I can.

Doug
I would like to see how it is attached. Mine have been disconnected amny time by accident and I have gone through the attach and check procedure. But no manual (to my knowledge) shows the correct attachments.

Please post a pict, Doug.
 
#16 ·
ill tell you what i did......

i went outside yesterday after whining on this post and took a look at my trap door in the hood vent. it too was open when the truck was off and on when the truck fired up.

I followed the top of the exhaust manfold to the end nearest the firewall and found a vacuum hose there. it had a one way thingy in it that only restricted the vacuum from the exhaust.

I had plenty of vacuum stuff lying around and put in a different restricter so that it let air flow go to the firewall....

ill be dang on if it closed the door when i pulled the vacuum hose off. and when i flipped it around and reinstalled it. the door popped open once i started my jeep.

PLENTY of free flowing heat. had to take off my hooded sweatshirt when stopped at a light. i had too much heat.

No photos i have no garage and its cold outside.. just look on the firewall where the vent side is and go less than a foot down and you will see a vacuum hose going to your manifold "behind carb" try it out if it doesnt work you can always flip it right back

post results so others who are less willing to try will when it works
 
#17 ·
jeepthg said:
ill tell you what i did......

i went outside yesterday after whining on this post and took a look at my trap door in the hood vent. it too was open when the truck was off and on when the truck fired up.

I followed the top of the exhaust manfold to the end nearest the firewall and found a vacuum hose there. it had a one way thingy in it that only restricted the vacuum from the exhaust.

I had plenty of vacuum stuff lying around and put in a different restricter so that it let air flow go to the firewall....

ill be dang on if it closed the door when i pulled the vacuum hose off. and when i flipped it around and reinstalled it. the door popped open once i started my jeep.

PLENTY of free flowing heat. had to take off my hooded sweatshirt when stopped at a light. i had too much heat.

No photos i have no garage and its cold outside.. just look on the firewall where the vent side is and go less than a foot down and you will see a vacuum hose going to your manifold "behind carb" try it out if it doesnt work you can always flip it right back

post results so others who are less willing to try will when it works
I did the same thing, but mines on tha intake manifold, not the exhaust manifold. it's got???

Firewall - vac hose - F/F rubber connection - Intake manifold

Are you saying flip the F/F rubber thing around?
 
#18 ·
ya ya intake manifold. i was drinking HEAVY.. lol

if the F/F rubber thing is a plastic trap like thing with one side dirty tan and the other side is blue or puprple i dont remember the color exactly.. the thing if pulled off blow into it. one side will free flow air and the other side stops it completely. you want the itake sending air to the firewall. not stopping it

yup all i did was flip the F/F rubber thingy around.. but i used a different one cause the size vacuum tubing didnt fit just right
 
#20 ·
jeepthg said:
ya ya intake manifold. i was drinking HEAVY.. lol

if the F/F rubber thing is a plastic trap like thing with one side dirty tan and the other side is blue or puprple i dont remember the color exactly.. the thing if pulled off blow into it. one side will free flow air and the other side stops it completely. you want the itake sending air to the firewall. not stopping it

yup all i did was flip the F/F rubber thingy around.. but i used a different one cause the size vacuum tubing didnt fit just right
Cool. Thanks, great find! I'll do this in a bit and takes some pics of it, it's routing and the other end to complete the write up on our little mystery here. This has been a fun thread.
 
#21 · (Edited)
OK, went out and experimented on mine.

In the cowl vent there are two flappers, one on pass, one on drivers side.

The drivers side one opens and closes via the /vent/heat/def setting. When off it's closed. The pass one seems stuck open, no matter what I do with vac or settings, it stays open. even bypassed the check valve and ran it without.

Also, had wifey feel for airflow by the vent as I manually closed the drivers side flap, she said the airflow stopped, makes sense since both flaps were closed.

I took out the check valve and even tried the strong port and man vac on the carb direct connected, made not difference.

The drivers side one definately seems to be cable controlled. The pass one vac controlled. Is that right?

So...(engine on or off made no difference in any setting)

Drivers side Flap
off=Closed
def/heat=Closed
vent=open

Pass side Flap
off=Open
def/vent=Open
vent=Open


A few questions..
1- Should both flaps open/close together? or are they independant?
2- How the hell do you get to the linkage/vac connections up there, I can't see squat.
3- What is the normal settings for these as I've outlined above, obviously something is not right on mine.
 
#23 ·
Hey no problem. I was wondering what that vacuum connection was for under there. Just a little advice on the pics. Go into your photobucket page and "edit" the pics to 640x480. That will help us old farts that can't see well and still 800x600 on our screens. By the way, I see you'll be hitting the big 55 in a couple of months.
 
#24 ·
Thanks for the pic. I've located mine, but I'm still a bit fuzzy by the term "flip around". Will the dark be in the middle and the green be on the end, or will the green stay in the middle and the dark will be on the opposite end. The opposite end currently being without.
 
#25 ·
Figured mine out... I'll edit with more detail in a bit..


Pass flap is vac actuated, Drivers is cable actuated.

My prob was the switch in the pic above has a plunger on the side of it. Int he off position, the lever bracket pushes this plunger in, releasing vac from the pass flap and closing it. When you move lever to Def, it releases the plunger and applies vac to the pass flap opening it.

That switch has a brutal amount of adjustment room, all held on with two little plasic nuts with 2 screws. It's easy to see how this could come out of adjustment simply with age, and hosing up the flap, either making the plunger stic in, closing the flap, or not contacting it enough to effectively keep pass flap open at all times, like mine was.
 
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