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Climate control panel (HVAC) is not working why?

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Okay. If you have now power on the orange wire, that is you B+ which gives the module power. You clearly need power there when it is turned on. Before you run power, just make sure you have power on both metal contacts on top of the fuse for that wire. If you have power on both sides, then I would clip the wire about 3 inches from that connector and run a new wire to about 3 inches from the other connector. Clearly, you want to make sure you have power on the wire from where you are clipping it on the fuse end, otherwise this would indicate the connector coming from the fuse box is the issue.

I drew on the diagram to give you an idea about what I am talking about.
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
CHASE6142001
  • MEMBER
  • 6 POSTS
Well, the battery hasn't been disconnected since I got it and it would work then go blank then work and just do that over and over until it finally stopped. So I changed the control head thinking that was the issue but it wasn't.
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
TAWAS23
  • MEMBER
  • 35 POSTS
Okay great. I did exactly what you said and ran a power wire from the havac/ecas fuse under the hood to a add a tap fuse wire and wired it into the orange B+ and have constant power now everything is now working like it should thank you very much for the help I really appreciate you taking time to lead me in the right direction. Thanks again it is nice having a honest go to place for issues we all need help with from time to time.
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Are you getting power to the wire I indicated? Also, if there is power, check for continuity to ground in pin 8 (see schematic above). It's the last wire on the picture.

Let me know.
Joe
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
MONTEB
  • MEMBER
  • 6 POSTS
  • 1991 CHEVROLET SILVERADO
  • 5.7L
  • V8
  • 4WD
  • MANUAL
  • 220,000 MILES
Electronic air conditioner/heater control module quit working. I have checked all relays and fuses and circuit breakers. I have traced out all wires and cannot find anything wrong. Do you have any ideas on the subject?
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
CARADIODOC
  • MECHANIC
  • 33,870 POSTS
Failed HVAC Computer. Very common problem. If you do a search, you should find a number of places that repair and rebuild them. If you know what to look for, you might pop the covers off and look for broken solder connections.
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Awesome! Good work.

Thanks for the update. That info will help others as well if they have a similar issue.

Glad to help. Please come back when you have more questions.
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
CHASE6142001
  • MEMBER
  • 6 POSTS
I used my test light only power it was getting was from the brown wires.
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
MONTEB
  • MEMBER
  • 6 POSTS
Where is HVAC computer located and what does it look like on my truck?
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Do you know the pin numbers the brown wires go to? Also, have you checked for ground?
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
CARADIODOC
  • MECHANIC
  • 33,870 POSTS
It is about a 5" x 5" black plastic box. The front of it is the control panel.
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
CHASE6142001
  • MEMBER
  • 6 POSTS
I don't remember the number and I couldn't find any grounds at the time when I was looking. It's been too cold and rainy to check recently.
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Okay. You create your own ground with a test light, so power could be present. However, if the system ground doesn't work, it won't work. I need you to check specifically pin 8 for ground. If you have ground and you have power to the unit, chances are you got a bad part. Was it new or from a salvage yard?

Joe
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
CYNDA R
  • MEMBER
  • 3 POSTS
  • 1991 CHEVROLET SILVERADO
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 118,000 MILES
Panel control went off the next time the truck was started, it worked but when I pushed the fan button to increase, it went black again. We checked the fuse and it looks okay. There is still heat coming out below. We had another control panel and put it in, but it doesn't work either. Any suggestions what to try next?
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
HARRY P
  • MECHANIC
  • 2,292 POSTS
If you raise the hood and look towards the back of the engine compartment, high up, near the firewall, there should be a fairly large bundle of wires. This harness has the power for that control unit. Start with simply jiggling it around a little bit while the key is turned on (engine not running) and the heat/AC is turned on. Have someone observe it to see if the power flickers on and off. If so, then you have a loose wire in that harness, which is somewhat common on older trucks. I'll get you a wiring diagram later on if necessary and we'll go from there. Go ahead and check like I said and report back here. I'll be online again later this evening. Good luck!
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
CHASE6142001
  • MEMBER
  • 6 POSTS
I have a parts truck I got it out of but the one that was in it. Never had an issue it would stop working I could wiggle wires behind the ash tray it would work again. I've heard that plug melts and it did but that isn't why it stopped because I fixed that after it fully quit and nothing.
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
CYNDA R
  • MEMBER
  • 3 POSTS
We did try what you suggested worked perfect. Thank you
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
I have seen that issue before. They are also known to have the printed circuit boards internally have solder joints crack and cause a failure. If you get a chance, check power and ground. If you have both, it should work. If it doesn't, I suspect it's bad.

Let me know if I can help in any way.

Joe
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
CHASE6142001
  • MEMBER
  • 6 POSTS
Okay, thank you.
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Friday, April 30th, 2021 AT 4:13 PM (Merged)
Tiny
GRAYDOG
  • MEMBER
  • 2 POSTS
  • 1991 CHEVROLET SILVERADO
  • 6.2L
  • V8
  • 4WD
  • AUTOMATIC
  • 265,000 MILES
My truck is a K1500 diesel. I recently acquired this truck, so I don't know the true history on it. I have replaced the AC control unit on the dash with a new unit from AC Delco. I have replaced all three actuators. Currently the AC almost works. The fan will blow on all three speeds as it should, MAX works, defrost will blow out the top of dash, AC will blow out the dash vents and heat blows out the floor vents. I have two problems with the control unit. The cold to hot button does not work. Instead of showing a single arrow, arrows are lit all the way across the display and will flash for about ten seconds. There is no way to adjust the temperature. Second problem, the button that allows a blended airflow between dash and floor vents doesn't work properly. If all air flow is coming through the dash, the position indicator has the arrow all the way at the top of the display. Press the button one time and the arrow steps all the way down to the bottom of the display. So it's all dash airflow or all floor air flow. It seems like there is some type of resistor or temperature sensor that's fried, but I have no clue what to check next. Any help would be appreciated. Thanks!
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Friday, April 30th, 2021 AT 4:13 PM (Merged)

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