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Air controls now only blowing super hot air 2008 LE

15052 Views 29 Replies 3 Participants Last post by  fibber2
No matter what setting I put on the controls it will only blow out air that is as if it is on the highest heat setting. The air conditioner light comes on and you can even put your hand on the compressor lines on a warm day and feel that they are cold and tell that the compressor is comming on. Also if you set the temperature to a mid position on a very cold day the heater only blows super hot air. All of the outlet positions work such as floor, defrost etc. but only the temperature seems stuck on hot. I pulled the control unit away from the dash and it all seems to be one piece. I don't know if there is a way to test to see if it is faulty or wheather it might be some where else that the air is not geting diverted. Any suggestions would be appreciated. Also Does anyone have a clue as to what this module is called and how much it might cost and where the best place to get it would be if I needed to replace it?Thanks,
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Re: Air controls now only blowing super hot air

By the way I forgot to mention it is a 2008 LE
Re: Air controls now only blowing super hot air

Where do you live? You probably need to see if the A/C is low on R134a. This can only be properly checked with an AC Gauge set.

Regards, JC.
Even if the air conditioner is low on freon and the outside air temperature is 35F the air comming in should not be max heater when the temperature dial is set on the coolest or a mid level setting. Something is stuck on the highest heat setting no matter where you put the temperature setting on.
Stuck on heat all the time is probably not a bad thing for today, but you probably will want that fixed before Spring gets here (assuming it ever will!).

The dash assembly is in two parts, with the knob control panel in front, and the AC Amplifier behind that. The dash assembly sends a signal to the airmix damper servo controller. That servo motor moves the damper that directs air to go thru or around the heater core (little radiator) in the HVAC box behind the center cluster. The LE model only has one temperature control servo & damper, and that motor unit is located on the right side of the HVAC box (at the left hand edge of the glove box). When these motors fail some people have report hearing a 'clicking' sound as the unit searches for the right position.

I can post some drawings to help you find that motor. Step one would be to see if it is receiving a signal from the dash controller. If you are lucky, it's just a dead/stuck motor. The dash modules can cost you something like $500, while the motor is maybe $100.

How about the rear AC? Is it responding to your change in temperature request?
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I checked the rear AC and it is blowing cold. I would appreciate any help in locating the servo motor or damper. I don't hear any clicking sound. As far as Spring goes. Here in Houston we have been having a much colder than average Winter but it just warmed up last week. It is now 78 F. so I need to get this heater off soon.
Want to trade? I am so sick and tired of snow & cold.....

I would tend to think that if the rear is working properly, then the basic microprocessor logic of the HVAC head unit is probably OK. It could still be a connection or wiring problem, but I wouldn't go and spend money to replace the control panel just yet. More likely it's just a motor problem on the HVAC box.

So lets start with this. These pictures are from the drivers footwell. Dual front (XLE/Limited) vs. single temperature (LE/CE). Unfortunately I don't have one from the passengers side. Next time I change the cabin air filter, I'll have to snap a few. But from the drivers side you can see what the servomotor looks like. It will be in the exact opposite position on the passengers side. If you remove the glove box door (like for changing the cabin air filter) you should see it on the left. Don't confuse it with the other damper motor that determines fresh air vs. recirculate air (air inlet). If in doubt, change the dash control and see what the fresh/recirc. does.

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This is the drawing from the split temp control system, so it shows both the drivers and passengers air mix (you will only have the passengers side and it will control one large flap within the box). There is a single electrical connector on the servo motor. Another night I'll see what I can find on the pinout. Start with simply monitoring for any motion of the attached cams when you change the temp control. It's always possible that the motor is fine but the cam levers are not engaged, or the flap and shaft within the box are not connected.

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Thank you very much for the info and the pictures. Today is the first day that I have been able to take the time out to take the lower glove box out and look for the things to identify. I am still looking to get my orientation on where everything is loacated.
I found the air mix control servo motor but it is hard to get to. I can see that the cams are not moving or trying to move. I need to get better access to it and find out why it is not activating.
There is a piece of ductwork that brings floor heat to the passengers side footwell. Removing it might give you more room to access the servo motor. 87212D. Looks like a single screw or clip holds it in.

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Here's a better image:

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Once I get to the servo motor. I am not sure how to tell if it IS the actual problem. I whish I could tell if it was getting the signal to activate but I am not sure as to what pins or signals to look look at or wheather they are just a pulse or a steady current. Any ideas? I whish I had a factory manual but I only have a Haynes manual and it does not give anything like that.
Here's the basic test for server motor functionality:

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Great! I just got the motor off and ran the car with the motor still attached to the harnness. When I ran thru the temp range there was no motion. Also the flap in the ducting is not stuck and the ac is blowing cold and the heater is blowing hot with an easy flip of the lever by hand. I will run the test on the motor.
I tested the motor and unfortunately the motor worked just fine in the test. When I plugged it back in the car harness and turned the ac back on it moved back to the heat position so fo now I will leave it off of the car or try to move the leaver to the AC position and disconnect it since the diverter seems to default to the AC mode and it looks like Spring has spring here for the most part of the time. I haven't checked how much the control unit in the dash is or even what it is called but I would imagine it is not cheap. If I need to replace it I wonder what the best source would be?
Excellent progress! Hopefully the motor is just dead and you'll have to replace it. But if it works we'll have to dive into the schematics and see if we can test the output of the 5 pin connector. I'm hoping it won't come to that as tearing into the control panel will get really expensive.
I to the control unit out and looked at the part #. I think it reads 84010-08130. Which brings up simular controls when Googled.
Ouch - I didn't see that you had an entry with bad news when I posted my comment at 3:57 PM. Let me think about this a bit and review the schematics to see if I can get any insight about how to troubleshoot this further.
OK, I've got some thoughts on this. Let me see if I can articulate it.

The flap is controlled by a servo motor. A servo motor is part of a closed loop system in that it provides feedback on it's position. The master control takes that feedback and adjusts it's 'request' signal to the motor to move or stop moving. Lets imagine that the temperature control on the dash has 20 clicks from COLD (at 0) to HOT (at 20). Move the dash knob from full cold (0) to midway (10), and it sends a signal to the motor to move from full cold towards hot. How far will the motor travel? Until the position monitor on the motor tells the dash controller that it has reached half way. How does it do that? It sends a signal to the variable resistor (terminals 1,2 & 3), and watches for it to reach the 50% mark. Once the dash unit gets the signal that the correct position has been attained, it cuts the power. What if it never gets told that it's successfully left the cold position and moved to the midpoint (ie. the position monitor is broken)? Chances are it might continue to push towards heat until doomsday because it's never told to quit!

So either the dash module has lost it's hearing and isn't obeying the servo motors positional signal, or the positional sensor circuit is broken on the motor, and the signal is never sent.

In the basic motor test you followed, you applied positive and negative voltage to terminals 4 & 5. The motor turned full one way, then the other. Terminals 1, 2 & 3 are a simple variable resistor circuit that's used by a sensing voltage to determine the position of the motor arm.
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