Climate control panel (HVAC) is not working why?

Hey Bruce Yarnell,

Do you have automatic climate control ag. can you set the temperature?
Or do you have manual A/C, no specific temperature control?

You have nothing from the controls at all?

The first check would be to check fuses.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Please check all fuses in the under hood fuse box.

From the diagrams fuses 17,39,48,55,60,70 are for the HVAC

Most likely the power to the control unit is fuse 39, this would cause the panel to completely no function.

Hope this helps.

Regards, Joe

Hey Bruce Yarnell,

I have attached the wiring diagram below.

This is different from the diagram I was originally looking at.

The fuses are in the fuse panel on the left end of the dash.

Fuses 22 and 26.

22 is live with ignition on
26 is always live/constant feed

If fuses have power and are intact then you will nee to access the HVAC control module to check If you have power and ground there.

The HVAC control module is situated behind the glove box, it is remote from the dash controls.

If you do have power and ground but the unit is still not working you will need to replace the HVAC module.

Regards, Joe

Hey Bruce Yarnell,

If you need to check the power/ground at the HVAC control module.

When you remove the upper glove box you should see the HVAC module behind.

It has 4 connectors.

The Power/ground is in the 2nd connector.
Pin 8 black/white is the ground
Pin 1 red/violet is permanent 12V
Pin 9 violet/grey is ignition 12V

With the unit plugged in back probe using pin 8 as your ground, ignition on, check what you have on pins 8 and 9. You should have 12V, If you do then the A/C control module should be communicating. I would advise replacing the module.

You will need to reprogram the new module to the vehicle order, you will need a scanner with this function.

If you do not have 12V move your black lead from pin 8 and put it on a known good ground.

If you now have 12V then you have a ground issue.

If you don't have 12V power supply wiring issue.

Hope that helps.

Regards, Joe

Hello,

This sounds like the HVAC control head has stopped working but to confirm the failure letting make sure it is getting power and ground.

Here is a guide and some diagrams to help you run some easy tests:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Here are some wiring and fuse panel diagrams along with the blend door actuator locations in case you need them. Check to see if the panel is getting power after checking the HVAC fuse. There are four fuses that run the system as you can see from the wiring diagram.

Check out the diagrams (below).

Let us know what happens and please upload pictures or videos of the problem.

Cheers, Ken

Good afternoon,

I attached the wiring diagram and the connector diagram for you of the unit.

There are 3 powers to the control that must be verified. There are 2 fuses that feed power to the unit.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Let me know when you are ready to do some testing.

Roy

Okay, that sounds more like an internal solder joint issue. Not uncommon after most companies switched away from lead based solder. The high tin stuff loves to fail. Do you notice it being better or worse if the temperature changes and causes the board to flex?
You could pull the init out and check the connections to it, It's very easy but don't do it when it is very cold, the entire trim panel just pulls off and if it's cold it can be more easily broken.
You tilt the steering wheel down as far as it will go, then gently start at one side and pull the panel off, there are multiple clips that hold it to the dash. Once it is off the control head comes off with 2 screws and clips.
One thing to do if you disconnect it would be that it needs to be calibrated. For this you simply re-install the parts, then remove the HVAC/ECAS fuse for 20 - 30 seconds. Re-install the fuse and start the truck. Don't touch the controls, the unit will re-calibrate in about a minute. You do this same thing if you put a replacement control unit in, just be sure the replacement matches the options your truck has.
It is possible to test the system further but it requires a scan tool to do much of it.

Good morning,

I attached a wiring diagram for you of the fuses as well as the control for power.

https://www.2carpros.com/articles/how-to-check-wiring

Check the fuses for power on both sides. This is not a visual test, it is a power test.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Check the pins I circled at the control unit. If you have power then the control unit is the failure.

Roy

1. Remove the instrument panel accessory trim plate.
2. Remove the screws from the HVAC control module.
3. Depress the control assembly retaining tabs and remove the HVAC control module from the instrument panel.
4. Disconnect the electrical connectors from the HVAC control module.

Hi,

That is great that you checked these fuses. However, the HVAC/ECAS is the one that gives power to the controls. The HVAC 1 is your ignition feed which needs to operate as well so that is good that these fuses are intact, but we need to make sure we actually have power going through them.

If we have power on the load side of the fuse but we do not have power at the component, then you have a wiring issue. I would go to the back of the HVAC control module in the dash and see what voltage you have coming in on the orange wire. By what you are saying it sounds like you don't have power. If this is the case, I would just run a new wire from the fuse to the module. I would just cut the wire about 3 inches from each end and splice in a new wire and then retest it.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

You are welcome. Please let me know what you find. Thanks for using 2CarPros.

Hi,

By any chance, did you have the battery disconnected recently? Take a look at this TSB.

1991 Chevy Truck K 1500 Truck 4WD V8-350 5.7L
HVAC Control Head - Inoperative, No Display
Vehicle Heating and Air Conditioning Control Assembly Technical Service Bulletins HVAC Control Head - Inoperative, No Display
HVAC CONTROL HEAD - INOPERATIVE, NO DISPLAY
Number: 93-44-1A
Section: 1A
Date: NOV. 1992
Corporate Bulletin No.: 261210
ASE No.: A7

Subject:
HEATER VENTILATION AIR CONDITIONING (HVAC) CONTROL HEAD INOPERATIVE - NO DISPLAY

Model and Year:
1990-93 C/K TRUCKS

The HVAC control head on some 1990-93 model year C/K trucks may not illuminate when the vehicle is first started. This condition is much more likely to occur after a battery disconnect or control head replacement but may occur after any ignition cycle.

The condition is not permanent, it stems from the control head not receiving a correct signal when the ignition is turned on.

Recycling the ignition switch may bring the control head back to normal operation. If cycling the ignition does not work, disconnect and reconnect the battery making sure that a good electrical connection is maintained when reconnecting (avoid "chattering" the battery line).
_________________________

If that isn't the case, I need you to check for power to the control head. See pic 3 for the power supply. Also, pics 1 and 2 are relevant to the power supply (fuse). Reconfirm the fuse is good. If it is, confirm there is power in and out of the fuse.

______________________

Here are a few links you may find helpful:

https://www.2carpros.com/articles/how-a-car-fuse-works

https://www.2carpros.com/articles/how-to-check-a-car-fuse

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

_______________________

Let me know what you find.
Joe