HVAC: Air Mix Control

Jose Diagnostician Indiana Posted   Latest   Edited  
Unsolved
HVAC
2009 Acura RDX 2.3L (K23A1) 5-spd (BWEA) — 5J8TB18549A008253
Climate Control Unit Goes Offline When Air Mix Control Motor Is Plugged

Assumed that the module was shorting the 5v ref voltage since the module was going offline as soon as I plugged the motor. I ordered a dorman part from Autozone and I noticed it was the same part number. I plugged it and same thing happened. I scoped the S5V wire “brown pin 5” & AMD-P - Grey Wire Pin 3 and both have 5v unplugged. S-COM Orange Pin 7 has no com activity unplugged, not sure what to expect here as far as com waveform signature. As soon as I plug the motor, the HVAC system goes offline with no activity and both 5v ref voltages drop to 0v for Brown & Grey wires.

What is convincing me now that this aftermarket control motor is defective by design is that the OEM testing says that pin terminals 5 & 7 should have a resistance of 4.2 to 7.8 kOhms at the motor → Please someone confirm if this is meant at the motor side terminal or harness side but from the motor, it is 0.8 Ohms which is a direct short. I measured the old control motor and it has exactly the same resistance. Perhaps someone more familiar with the signature waveform may help on this. Thank you!

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Justin Mechanic
Tennessee
Justin
   

Looking at your wiring diagram, I’m wondering if S-COM Orange doesn’t stand for “communication“ but instead for ”common” ground. If you notice, that wire is linked to other units and leads to a box that reads “see ground for climate control sensors circuit”. Go back further in this story to help me. What lead you to the air mix motor initially? Did the car come in with the climate control unit…

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Jose Diagnostician
Indiana
Jose
 

Yes, it is a ground, i forgot about that. I did test it with a test light. The climate control was unplugged for this car when I first got it. When I plugged it back, the whole climate unit would shut off completely as if it was shut off. When I unplug it, it works again.

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Justin Mechanic
Tennessee
Justin
 

I think I would check the mix motor on the other side to compare, but it sounds to me like you have a defective new part.

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Michael Technician
Indiana
Michael
 

Jose, So, you have one side that functions, as long as you don't plug this one in. GREAT, lets use that to figure out how they are making this thing work. This is my guess of what these pins are. If you can access the other side you will be able to confirm exactly how this thing is supposed to work, My guess is that the pins are wrong, and you end up finding that you have to get one for the…

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Jose Diagnostician
Indiana
Jose
 

Mike, this confirms my theory and the reason there must be some sort of high resistance between pin 5 & 7 based on the position of the sensor, since the resistance in my case is basically nothing, the ground and ref signal are shorted as soon as it is unplugged so the 5v is lost from the module and shuts off all controls that depend on the ref signal. Unfortunately I can't source the part…

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