Adjust Stepper Motor Limits for Blend Door?

I was hoping for some help with my 2000 Jeep Cherokee (XJ) heat and AC issues.

This past winter I noticed I didn't quite have the hottest heat when the days were cold enough to use it. I live in Cincinnati so we had some days in the 20's and even 10's where this was a big issue for me. I had the heat all the way hot and it was just barely warm, but when i turned it to cool, it would get cold and there were different temperatures in between, so the blend door was moving and stopping in the right places. I heard that the blend door broke sometimes and similar issues were experienced, but it got warmer outside and I let it slide.

Now its summer and I am HOT!. I can run the AC but its not quite cold enough. I finally got up the nerve to pull the stepper motor off today, and I feel a hard stop at both points. Also when I have it in the heat position, I get the hot air like I'm supposed to. More importantly, when I move it to cold I get ICE COLD AC. My conclusion regarding the blend door is that it is not broken.

I believe that my stepper motor is not moving all the way to its stop points. When I look at it with it still plugged in and vent or AC running, it doesn't move all the way to the stop points on the motor. Is there a way to reprogram the stop points manually so that the motor will actually have a wider swing? I know that this is the opposite of what is normally the issue, but I'm almost positive this is the fix, as I've already tested it by moving the door by hand while running the heat and AC (btw, had my AC system checked, I have a full charge with 38lbs suction. Both fans, mechanical and electric for the condenser and the radiator are functioning properly. My radiator and heater core have been flushed and filled with the correct amount of antifreeze. My temperature typically runs 190-195 and just above 200 in sitting traffic 90 degrees outside. I flushed the heater core myself and it flows just fine, with no leaks.)

In conclusion (lol) I really just want to know how to adjust the stepper motor limits so that I can get it to make the blend door to make a seal. I also understand that if I adjust the points too far I could then break the blend door--- in which case I'll have to send heatertreater both an email and money .

Any help you could supply would be just splendid, so i don't have to drive around with my finger on it... kidding...

If you can't help, I understand and I'll probably just copy and paste this to a jeep forum so I can get made fun of for writing too much... (I did.)

Thanks

Mike

Ok, I have a little information back from Heater treater. He said there is a resistance strip tied to the gear in the stepper motor. I opened mine up and I don't have said strip, but I do have a potentiometer tied to the main gear.

When I put my Fluke on it, I get 6.5k ohm before the pot goes open. the pot does not have a hard stop in it. I'm wondering if maybe this pot is supposed to go to 7k or 8k before it goes open... That's assuming that when the pot goes open is the point that make the stepper motor stop turning. In the pic, the blue gear is what drives the potentiometer.

pics

I don't think it's a stepper motor... but I could be wrong. The only stepper motor I am aware of in the XJ is the idle air controller, which controls engine idle speed.

Mike, Kastein is right it's not really a stepper motor. I took mine apart last summer out of curiosity and the gears fell out before I got a good look at them. I know stupid. Anyway It went back together and it still works fine. I had to line up the grease smears on the gears to get a good idea where it should go back together. Then holding it carefully while apart reconnect the electrical connector and test the cold to hot range with the dash switch. Had to make a few adjustments to get it back spot on but it is possible to do. IIRC there is a range mark on the outer housing that should align with a mark on the metal drive hub. Be patient you will get it.

Thanks for the replies! I think I'm learning more than I want to about this thing, but oh well. Its a growing experience.

Greenz said:

Mike, Kastein is right it's not really a stepper motor. I took mine apart last summer out of curiosity and the gears fell out before I got a good look at them. I know stupid. Anyway It went back together and it still works fine. I had to line up the grease smears on the gears to get a good idea where it should go back together. Then holding it carefully while apart reconnect the electrical connector and test the cold to hot range with the dash switch. Had to make a few adjustments to get it back spot on but it is possible to do. IIRC there is a range mark on the outer housing that should align with a mark on the metal drive hub. Be patient you will get it.

Click to expand...

I have since realized that it is not actually a stepper motor, but it is controlled by a pulse. The easy way to align it up again is to use what you mentioned about the rang mark, there is also one on the potentiometer that should point straight toward the motor when the range mark is aligned.

However, having taken it apart and put it back together does not solve the issue that it does not move far enough. I can move the pot gear over a few teeth to make it work for AC, but then I can't go far enough for heat and will have to change it the other way for winter. Is there a way to make it swing further?

Unfortunately the pot may be worn out. IIRC when the blue gear was left out, the motor would free spin in either direction. When the pot was at a zero point(centered) physically and dash temp switch was at center between hot/cold point, that is when you put the blue gear back in, centered. I do remember it was a lot of trial and error to get it right. at least you have a picture to go by.

Not to be funny, but have you spent enough time screwing with it that buying another one from a salvage yard might be the next appropriate step? While repairing it yourself is laudable, there will always come a time when a change in course is prudent.

Your earning potential is $75 p/hour, you have worked on something for two hours without success, a replacement part is $15 and takes 10 minutes to install. What do you do? What do you do?

OK, new information. TO start, I don't think there's anything wrong with the motor. I believe it is the head unit in my dash. When i have the motor plugged in in my hand and i turn the knob, it doesn't go all the way to the extents (already knew this). I decided to set the knob in the middle, with the motor's position in the middle as well, and go through each click on the knob until the motor stops moving. I found that the first click on cooling and the last click for the highest heat do absolutely nothing. It doesn't even send the signal to the motor.

I've concluded that I will need to buy a new head, which seem to run from $25 used to about $60 new. I'll buy new.

If anyone else has this problem and doesn't want to spend the money on a head right away (like me), you can set it up to work for cooling and a little bit of heat, which is fine for summer, and then switch it to more heat for winter.

I hope the head unit is the issue...

joe_peters said:

Not to be funny, but have you spent enough time screwing with it that buying another one from a salvage yard might be the next appropriate step? While repairing it yourself is laudable, there will always come a time when a change in course is prudent.

Your earning potential is $75 p/hour, you have worked on something for two hours without success, a replacement part is $15 and takes 10 minutes to install. What do you do? What do you do?

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lol Joe I get where you're coming from. I'm the biggest fan of changin parts out but as soon as I opened it up it reminded me of my younger days pullin apart RC cars. Needless to say, I got caught up in the moment, and it was just flat out interesting that it probably took a team of four or five people to come up with something like this, that had easily been managed by a simple CABLE for like... 80 years? You have to wonder why they didn't ask themselves what you asked me? (Bossman) "Hmm Jim, what do you think if we spend 80 hours @$75/hr to develop a motor for climate control?" (Jim) "I dunno boss... wouldn't it be more cost effective to buy a cable for $1? I mean, it is a Jeep, right?" (Bossman) "you think you know better than me? The people will love me for this! You're fired!"

Too much?

Yeah, but the parts counter can only charge 5 bucks for a cable (400% markup) while they can charge $200 for each half of the motor assembly (probably costs around 10-20 to build each one.)

I have one stuck open I believe and it sucks with this 90 degree weather

So after much research and even checking the FSM I haven't found any procedure for this so called alignment. Is it only needed if you disassemble your blend door motor, or do I need to do something special when I install the good used motor I pulled from my parts Jeep?

scoobyxj said:

So after much research and even checking the FSM I haven't found any procedure for this so called alignment. Is it only needed if you disassemble your blend door motor, or do I need to do something special when I install the good used motor I pulled from my parts Jeep?

Click to expand...

After playing with the motor I figured out it self adjusts. Doesn't matter where you put the dial the motor will move to that position as soon as you plug it in.