Low air flow from heater fan
 

It seems like there's not much air coming out of the vents on my '01 Cherokee. The fan sounds like it's working well, it definitely speeds up as you go up through the positions. But with the fan on high it doesn't put out much more air than some of my other vehicles do on low. It doesn't seem to matter where I have the air coming out, floor, vents or defrost all seem to have pretty low flow.

I'm thinking that most likely there's some blockage in the air ducts before the diverter valve. This weekend I hope to dig into it a little, but I was wondering if anyone had any suggestions of where to start looking. Do Cherokees have a cabin air filter that might be plugged? Is there a screen somewhere that tends to block up? Or is the heater core the most likely place to get blocked?

Thanks

the best bet is that one of the blend doors is either broken or the motor to move it has broken. youll have to tear into the HVAC

Do you see this problem with the Mode Selector in the Recirculation setting (first setting up from OFF)? In Recirc you are bringing air in from the cabin instead of the outside.

You can see the Recirc door and a portion of the fan by rolling the glove box down (two rubber stoppers removed) and, using a flashlight, looking inward towards the HVAC unit. With vacuum available (engine running) move the Mode Selector knob to Recirc. You should see the door open. The door also defaults to open when the Mode Selector is positioned to OFF.

If there's any rat's nest materials or foam seal materials in there you should be able to see it. Operate the blower and see if the fan is rotating. It could be loose on the motor shaft. You can poke the fan through the recirc opening grill using a screw driver (fan turned OFF). See if it flops around. If everything seems okay, there may be crap downstream of this point.

Edit: If the airflow is normal when Recirc is selected there could be blockage upstream of the fan. The fan brings air in from the grill under the windshield wipers.

I'm thinking that the blend doors are working correctly because the air comes out where it's supposed to: floor, vents or defrost, whatever is selected. It's just not very much air.

Thanks, that gives me some more specific things to look for. I don't know right now if "recirc" makes a difference, but that will be easy enough to check.

By the way, just from the sound I believe the fan is working correctly. It certainly changes its sound as well as the amount of air in each of the 4 speed positions. The motor sounds like it's under some load, like it's trying to move air, not just freewheeling. And there are no unusual noises to indicate bad bearings or anything. So I'm thinking a blockage somewhere is likely.

Again, thanks for the specifics on where to look. Now I know what I'm doing on Saturday!

Here's a pic of the recirc air door, as will be viewed through the glove box opening. This pic does not represent what a glove box roll down looks like - it's a view of the glove box completely removed.

I wonder why this thing is still called a "Glove Box". I don't think anyone has put gloves in that box for decades. LOL

Attachment 319853

Found a mouse nest inside the fan cage when that happened to me. No air volume out of any of the vents, in spite of the fan obviously running well. Had to pull the fan out and clean out all the stuff the mouse had put in there. Haven't the slightest idea how a mouse could get in there, but they're tricky little devils.

You're not the first to find baby rat nesting materials in there.

I too am wondering how they get in there. They can slip through the eye of needle so I suppose they could sneak in through the the grill under the wipers, even though there's a screen to prevent that. Through the recirc opening? The recirc door defaults open when the system is shut down, but how do those buggers get in the Jeep to begin with?

I know...most floor boards are rusted so bad under the front wheel well liners that they climb through the rust holes in the floor.

I catch Chipmonks and Red Squirrels jumping up in my wheel wells all the time.

I think I've located the problem, but I don't think I like what I've found. The air flow is pretty much the same whether it's on recirc or not, so that must mean it's either in or downstream of the blower.

I can see the blower through the recirc door. It's clean and spins freely, so that must mean it's not the blower.

From what I can see in my service manual, it looks like the air flows from the blower, through the AC evaporator, to the blend door. Then, depending on the position of the blend door, none, some or all of the air goes through the heater core. From there it looks like the air, whether it went through the heater core or not, goes to the floor, panel, or defrost, depending on what is selected.

So I tried it with the heat turned all the way up and all the way down. There's good flow with the heat down, but it slows way down when I turn the heat up. So what it looks like is that the air flow through the heater core is restricted.

It sounds like a lot of work to get the heater core out of a Cherokee (evacuate the refrigerant, disconnect the refrigerant lines, drain the radiator, disconnect the heater hoses, remove the dash, remove the HVAC assembly).

So my questions: Am I right in what it takes to get at the heater core, or is there any short-cut? Is it normal for the heater core to significantly restrict air flow, or does it sound like there is a blockage?

If that's really what it takes I'm not going to go any farther with it myself. And I don't want to spend the money on someone else doing it if this is just normal.

I think your analysis is correct.

HVAC Unit R&R is a hard job. If you can get by with airflow with a blend of heat and cold maybe you should leave it be for now.

OK, thanks. I wish the answer was something better, but it's nice to know what reality is. It usually works out better that way. I think I'll check with my shop and see what they think it will cost. Not sure I'm going to pay it, but Minnesota winters are a lot less fun without effective heaters!

Here's something you may want to experiment with:

Locate the AC Accumulator in the engine bay. Remove the electrical connector from the Low Pressure cycling switch on top of the Accumulator and tape the harness connector and switch over with electrical tape to protect them. This will prevent the AC Compressor Clutch from engaging.

Now, you can use any selection on the Mode selector and the AC cold air won't be involved in the Blend-Air door position, only outside air. Except that if you select Recirc the cabin air will be recirculated without having your heat diluted with cold outside air.

Any selection on the Mode selector can be used for heat. Adjust your temp selector to get optimum air flow and heat.

The only draw back with this is you won't have AC air to help defogging the windows.

Edit: You can always plug it back in if you are having defog issues (above 30*F).

If I'm understanding you correctly, the only real advantage this would have is allowing me to use the recirc position without running the AC. This would let me get warmer air because recirc doesn't bring in cold outside air, but it normally uses the AC to cool the inside air, and with the low pressure cycling switch disconnected it wouldn't run the AC.

But it wouldn't have any effect on the output with the mode selector in the "floor" or "panel" positions that don't run the AC.

Am I getting that right?

You are correct.

I'm fixing to do this to my Heep shortly because winter is coming. Last year it got down to 13 below zero so I do enjoy having Recirc and the panel/floor selection with heat only.

OK, got it. Thanks for the suggestion.

By the way, I sort of did something like that on a CJ5 a long time ago. I was replacing the rusted out tub with a fiberglass one and I never bothered to cut the air opening in the cowl, so the heater just pulled air from under the dash. I figured a heater in a rag top needed all the help it could get.

I did something similar on my '90 to have the floor/dash panel combo or recirc with heat only, but to accomplish it, I cut the wire from the selector switch that signals the A/C system and installed an inline switch on the dash board to disable the A/C whenever I want.

i have a similar problem with air flow. all actuators work as i cycle through the positions.
if i remove the blower motor resistor the air flow will knock you over. i found out the blend door regulator wasn't working so i removed it and operated it manually. no change. it seems as though no air gets past the evaporator. previous owner said that he had the evaporator and blower motor replaced. guy told him he knocked off a vent when he did it. that doesn't make sense to me. i am new to this and have the dash tore out and access to the evap box. is there another door other than blend inside it? by the way 2000 cherokee sport

Well if the blend-air door actuator is not working what's the mystery?

'99 thru '01 Blend-Air Door circuit:


Attachment 312257

the problem is, that i removed the regulator and was able to move the blend door by hand. there was no change in the air flow. is there any other door inside the evaporator? with the blower motor resistor removed, i can see the evaporator, if i look from the other side i can see the heater core. i don't want to tear out the whole assembly if there is any way to avoid it.

Disregard any previous posts, what is your problem exactly?


No heat, No AC? What?

heat works, air works, just very little air flow. i am unsure since i haven't pulled the heater box yet. i am new to this so my understanding is limited. i thought that the blend door was to control the mixture of hot and cold air that was pushed through the vents. to me, it would seem that the blend door is the only thing separating the to sides, hot and cold. if i am able to put a light into one side or the other, i should be able to see that light if the blend door is somewhere in the middle. i get no air past the a/c side.

Is that very little airflow from any outlet?


Does the blower fan speed change with any of the four settings selected?


Does the airflow change when MAX AIR (recirculation) is selected on the mode selector?


The Blend-Air Door is the device to 'blend' cold and hot air. All other doors in the HVAC Unit divert the air to the selected outlets.


Some pics of inside the HVAC Unit - Bottom half:


Attachment 312246


Attachment 312247


Attachment 312248

thank you for the pics. fan works all speeds. i have the dash out and can see all vent doors working. i move the blend door manually and no change in air flow. recirc door works as well. i must have blockage. i am going to buy an inspection camera and see whats going on. it will be worth the investment if i don't need to tear out the hvac box. thank you. i will post with the results.

You can remove the blower resistor block and see if you see crap in the blower chamber (nesting materials from critters).


Attachment 312244


If so. you may be able to suck some of it out using a shop vac. otherwise you'd have to remove the blower to remove it.


Attachment 312245


With the Recirc air door open you can also see the blower fan. With the fan off, reach in with a screwdriver and gently touch the fan and see if it is secure. Also, see if it turns freely.


With the Recirc door open, key to RUN/ON, turn the fan speed to 1 and see if the fan is turning.

got my scope and couldn't see anything. so i hooked everything back and nothing. fan wouldn't spin. i got to checking the wiring, when they replaced blower motor they wired it backwards. i am a genius for not realizing which way the motor was turning. but now i am troubleshooting the whole circuit. i am only getting 4 volts to the motor. when i hooked it up to a 12 volt source it spun like crazy. my guess is the resistor went bad after all of my in and outs. thanks for all the pics and diagrams. i am sure i will have it rolling soon.

FINALLY! got to moving stuff around and everything works. i don't understand, probably should care, but, i got it all put back together and it works. the only real issue was the blower was reversed. i felt air through the resistor hole and thought it was okay. learned a lot and truly appreciated the support. now for the tcm code i got...

What TCM code?

1698, cel was on when i got everything back together. i looked it up, said no communication between ecm and tcm. also saw one that said the battery was disconnected too long. hoping the latter but, that doesn't makes sense to me. haven't had time to do anything else.

I finally got around to (or more accurately, decided to pay for) figuring out the problem on my '01. As a reminder, I had good airflow with the blend door in the cold position, but the flow dropped off as the door was moved to hot.

The solution started as CCKen said to golftoad. Taking out the blower resister block showed a mouse house on the evap coil. After removing the heater box we could see that the evap coil was about half obstructed. But that would reduce air flow at any temp setting, so that couldn't be it (although it certainly needed to be cleaned out).

There was a little bit of debris (that had snuck past the evap coil) on the air inlet side of the heater core, but not enough to make a difference. But holding the core up to the light you realized that you couldn't see light through it! A bunch of fine debris had come past the evap coil and worked its way deep into the heater core fins. I decided to replace the heater core and the (leaking) evap coil with new while everything was apart. Now there's good air flow at any temp setting!

Just thought I'd close this out for anyone who stumbles on it later.

Attachment 311679

I replaced the blower motor resistor/ controller several years ago but have had very poor air flow since. Now after reading several forums, I checked the blend door problems but they appeared fine. I could find no obstructions. The fan engaged into high.After reading on jeep garage.org... of some having the blower fan running the the wrong direction I checked and sure enough my fan was turning the wrong way. I give fault to the resistor/controller being wired wrong as when it is installed the wire clips can only go together one way. I had to cut the lead wires (green and brown I think) to the blower motor and reverse the wires. The blower now turns the correct way and air flow is restored. bygeorge