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03 Suburban rear HVAC not working

Celerity
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Celerity Enthusiast

Celerity

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Hey all !

 

Just signed up, but I'm coming over from gmc4x4.com. That forum has pretty much died out, and I need some pretty urgent help.

 

Rear heat !  Fan doesn't spin. Doesn't get voltage at the fan.  I have done the following, but I am willing to double check things too:

 

  • That red wire under the dash. Complete, charged and seems to be ok. I really don't understand this fix, so I'd be willing to talk about it some more.
  • Replaced rear resistor with the new updated one. Millivolts on those wires - nothing else.
  • Fuses checked and appear to be ok.
  • I have the auto-thermostat model with rear and fore temperature settings and "Auto" fan speeds. When I move the front HVAC control, it will disable the rear (Unless it's in AUX and the rear comes to life)
  • The vent flapper doesn't appear to move either.  It's like the entire rear unit has just gone to sleep.
  • Voltage applied directly to the motor will spin it. Motor and windings appear ok and test out ok.

 

Does anyone have any ideas ?

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carnau
carnau

I have run into a lot of Control Processors causing this issue. If it doesn't work nothing will. Here is the Schematic. Check the Power coming into the Processor on circuit 1740 and the Ground on 1450

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SpartanAutoworx Enthusiast

SpartanAutoworx

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Check for voltage on the left rear pillar should have one connector with 4 wires. Two of them should be orange in that connector of a pretty good gauge wire. I bet you have voltage to only one of the orange wires.

carnau Enthusiast

carnau

Posted
Posted

I have run into a lot of Control Processors causing this issue. If it doesn't work nothing will. Here is the Schematic. Check the Power coming into the Processor on circuit 1740 and the Ground on 1450. If you got power and ground check the Power and ground from it to the blower motor. If you have power coming to the Processor and nothing coming out. That's the problem.

 

Part Number - 15-73506

http://amzn.to/2i2vhCb

 

Don't forget to hit the Like button if this helps!

879570.gif

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Celerity Enthusiast

Celerity

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55 minutes ago, SpartanAutoworx said:

Check for voltage on the left rear pillar should have one connector with 4 wires. Two of them should be orange in that connector of a pretty good gauge wire. I bet you have voltage to only one of the orange wires.

Wait, which left ?  On the side of the HVAC unit ?  I only know of one Orange wire, and that surely has very little voltage on it. like 300 mv.  But I'm not aware of the other one you're talking about. 

 

So yeah, you're already correct. One of them doesn't have voltage. Now what ?

Celerity Enthusiast

Celerity

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26 minutes ago, carnau said:

I have run into a lot of Control Processors causing this issue. If it doesn't work nothing will. Here is the Schematic. Check the Power coming into the Processor on circuit 1740 and the Ground on 1450. If you got power and ground check the Power and ground from it to the blower motor. If you have power coming to the Processor and nothing coming out. That's the problem.

 

Part Number - 15-73506

http://amzn.to/2i2vhCb

 

Don't forget to hit the Like button if this helps!

 

Now this is pretty good stuff.. that schematic though.  Where did you find that, the Necromonicon or the Darkhold ?  That thing is so hard to understand !  I'll look for the unit itself and just measure some voltage.   Tonight, however, is some kind of record breaking McMurdo station cold out there.  I'll give this a run in the morning. Thanks for the amazon link too !

SpartanAutoworx Enthusiast

SpartanAutoworx

Posted
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2 hours ago, Celerity said:

Wait, which left ?  On the side of the HVAC unit ?  I only know of one Orange wire, and that surely has very little voltage on it. like 300 mv.  But I'm not aware of the other one you're talking about. 

 

So yeah, you're already correct. One of them doesn't have voltage. Now what ?

 Right side of vehicle   Passenger side  

 

 I'm used to customers always thinking it's  looking through the window. 

 

 So passenger-side the right side  four pin connector with two orange wires. 

Celerity Enthusiast

Celerity

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On 11/10/2017 at 9:17 PM, SpartanAutoworx said:

 Right side of vehicle   Passenger side  

 

 I'm used to customers always thinking it's  looking through the window. 

 

 So passenger-side the right side  four pin connector with two orange wires. 

Alright, so it appears the large orange wire isn't getting voltage. The other one is - Which is kinda what I was saying. That large orange wire is the supply for the resistor.

 

The smaller orange wire - What is it ?  Where does it go ?  What's next ?

Celerity Enthusiast

Celerity

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On 11/10/2017 at 6:08 PM, carnau said:

I have run into a lot of Control Processors causing this issue. If it doesn't work nothing will. Here is the Schematic. Check the Power coming into the Processor on circuit 1740 and the Ground on 1450. If you got power and ground check the Power and ground from it to the blower motor. If you have power coming to the Processor and nothing coming out. That's the problem.

 

Part Number - 15-73506

http://amzn.to/2i2vhCb

 

Don't forget to hit the Like button if this helps!

 

Ok, I have power going in, but the orange wire on the output (grey) connector is giving me 2.67 volts regardless of knob position.

 

sound about right ?

Celerity Enthusiast

Celerity

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Looks like the input voltages on the input side are there, but the output side is running ~3 volts. But on the orange cable to the fan resistor I get 0. 

 

Still not sure how this box works. The rear panel stops operating (Says "OFF) when I disconnect the module. The voltages don't change with the knob (But I don't think it should)

 

 

carnau Enthusiast

carnau

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It should only be a 3 wire connector. Black , Purple, Orange. The orange wire should have Battery voltage. Does it have battery voltage? Not on the resistor. On the processor.  

Celerity Enthusiast

Celerity

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6 minutes ago, carnau said:

It should only be a 3 wire connector. Black , Purple, Orange. The orange wire should have Battery voltage. Does it have battery voltage? Not on the resistor. On the processor.  

Yeah that one there is dead.  I get millivolts on the purple and orange, the black is ground and is continuous to ground.   This is the problem.  It's dead.

carnau Enthusiast

carnau

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Posted (edited)

Well the Next step would be to check the RR HVAC Fuse Under the hood. It is a 30amp fuse. See if it is good.

Edited by carnau
Celerity Enthusiast

Celerity

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Done and Done. Fuses are all ok. I'm getting power to the hots on the control module, and I am getting voltage on the orange under the dash.

 

Next is why I'm not getting voltage on the wire - which if I'm to understand that Darkhold schematic, that should be hot all the time .. like it's the same wire. 

 

But I get power to the control module, and then I get nothing but 3-4 volts FROM the control module at all times.  So I am getting on the side that the control module is bad.  But I'm still not sure. I think after this there is nothing left to replace.

 

If that orange truly is dead, then the control module shouldn't work either.... Right ?

SpartanAutoworx Enthusiast

SpartanAutoworx

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4 hours ago, Celerity said:

Alright, so it appears the large orange wire isn't getting voltage. The other one is - Which is kinda what I was saying. That large orange wire is the supply for the resistor.

 

The smaller orange wire - What is it ?  Where does it go ?  What's next ?

Look up the connector for c397

The two orange wires should have 12volt battery positive voltage

If that other wire is dead I would say you need to trace it back for a break in the wire. 

I bet you put 12volts to the wire you will be back in business.

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