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My heater nor a/c does not work. I can apply 12VDC to the…

Customer Question
Hello, my heater nor...

Hello, my heater nor a/c does not work. I can apply 12VDC to the red wire coming from the fan relay going to the fan and the fan will work. I have replaced the rear fuse box, body control module and test or replace all fuses and relays. It all started when my sister ran over some debris in the yard. The vehicle is a 2004 Chevy Trailblazer.

Mechanic's Assistant: How many miles are on the car? Has the car been starting normally?

Around 120,000 miles. The car starts fine

Mechanic's Assistant: What is the model/year of your Chevy?

2004

Mechanic's Assistant: Are you fixing your vehicle yourself? What have you tried so far?

Hello, my heater nor a/c does not work. I can apply 12VDC to the red wire coming from the fan relay going to the fan and the fan will work. I have replaced the rear fuse box, body control module and test or replace all fuses and relays. It all started when my sister ran over some debris in the yard. The vehicle is a 2004 Chevy

Submitted: 4 months ago.Category: Chevy
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Answered in 15 minutes by:
3/12/2018
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 4 months ago
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 30,400
Experience: GM Grand Master Technician 2007. 14 years experience.
Verified

Hello there, I am Cam.

I am Licensed technician at a GM dealership with more than 16 years experience. 
Like you, I am a user of this website and as such, any billing questions should be sent to customer service.

I ask that you please provide details and communicate with me so we can make your experience here worth 5 stars! I am around most days but not every minute of every day. If you reply while I am offline, I will respond when I am next online. 

I am reviewing your request and will post in a moment.

Does your front system seem to even change temperature ? Does it change modes?

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Customer reply replied 4 months ago
Nothing at all. The compressor engages but the fan won't blow at all
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 4 months ago

Ok, the compressor engaging is good, it does mean the head is getting power.

Is this a digital display or manual sliders?

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Customer reply replied 4 months ago
manual sliders
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 4 months ago

Did you happen to take the connector off for the resistor beside the blower motor and check the condition of the wiring and terminals in that?

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Customer reply replied 4 months ago
I checked the connectors and changed the module with a new one. I have voltage at the red terminal of the module coming from the fan motor but no voltage coming out the seven pin connector on the module. I can also apply voltage to the red wire coming from the fan motor and the fan works without grounding the black wire. Most of the gages on the dashboard doesn't work, but the fan was working fine until my sister ran over some debris. I have cleaned the multi ground connector under the carpet. I have replaced the rear fuse box and had the body control module replaced and programed.
Customer reply replied 4 months ago
Also replaced the temperature control unit
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 4 months ago
Ok so there is more than one fuse for this. I’m on my mobile and won’t be at the computer for an hour but check for a second fuse.
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Customer reply replied 4 months ago
Where's it located.
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 4 months ago

One is fuse 35, a 40 amp in the underhood fuse block, the rest are fuse #'s 36, 39 and 44 in the rear fuse block.

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Customer reply replied 3 months ago
Sorry for not responding sooner.All of the fuses check out.
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 3 months ago

Question, you mentioned a red wire from the fan to the resistor, the 2 wires to the fan from the resistor should be black and purple. Did you splice into a purple one?

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Customer reply replied 3 months ago
The resistor I have has a black and red wire. I bought it from Orileys Auto Parts Store
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 3 months ago

Can you test the wires into the resistor pack and see if they have power and when, meaning what position the dash dial is in for the fan speed.

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Customer reply replied 3 months ago
I've tested the voltage coming from the wiring harness with the seven pin connector. I have voltage at the harness, but no voltage at the red wire coming from the resistor no matter what position the fan speed control knob is on
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 3 months ago
If you have voltage into the resistor and none out then it’s a faulty resistor.
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Customer reply replied 3 months ago
I've replaced it 3 times
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 3 months ago

Do you have a test light that you can use to check for a bright light vs a voltage?

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Customer reply replied 3 months ago
Will try when I get home
Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 3 months ago

Ok.

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