[mdmartin]

Disclaimer
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A 355nation How To presented by
mdmartin

Project Name
How to keep re-circulation mode on all the time, regardless of vent setting, to avoid unfiltered outside air inside the cabin

Project Description
Modifying the HVAC control panel to avoid it disabling the re-circulation mode in the windshield defrost settings. Allows the re-circulation mode to be used in any vent position setting, whenever the recirc button is selected

Skill Level
Moderate

Project Vehicle
Make: Chevrolet
Model: Colorado
Year: 2009
Engine: 2.9L
Power windows: Yes
Sun Roof: No

Tools Needed
7mm socket; dremel cut off tool; superglue

Project Time
1 -2 hours

Project Cost
Effort


Many have expressed frustration that the Colorado does not incorporate a cabin air filter in the HVAC system. This leads to dirty and dusty air from the outside being blown inside, especially when the vent selection knob is in either of the defrost settings, because it will automatically disable the re-circulation mode, even if it is selected with the button. It does this with a micro switch located inside the HVAC control panel, in the travel of the vent position selection knob. This is how I 'tricked' it to always see that knob in a position that allows for the re-circulation mode to be used regardless of what selection is actually made.

1. First, remove the center trim panel, exposing the screws on the sides of the HVAC control. Remove the screws, and remove the control panel. There will be electrical connectors on the back, as well as the control cables for the temperature and vent control. This is explained in more detail in the "How-To Change the color of your HVAC controls"
   
   Now the control panel is removed. In the "How-To change the color of your HVAC controls" write up, @rshadd indicates that the vent position and temp select knobs can be pulled off with pliers. I tried this, and despite very considerable force, could not get either to come off. Regardless, the rest of the procedure does not require any further opening of the control panel.
   
   
2. On the back side of the control panel, you will see the back of the vent selection knob rotates a black bracket on a gear assembly:
   
   
   
3. You will want to remove this black bracket by rotating it to the center position, and pulling back on the top of it to pop it off. There is a key on the gear it turns on, so it will be easy to put it back in the correct position. You should now have the black bracket by itself:
   
   
   
4. Now, you can see that this bracket has a thin tab that sticks into the back of the control panel. This tab hits a micro switch when it is in the "Dash and Feet" vent position, which allows the re-circulation mode to activate if the button is selected. We want that switch to always be made, regardless of where the actual knob is. So put the black bracket in a vise, and use a Dremel tool with a cut-off wheel to cut that tab off the bracket, but MAKE SURE to leave some of the wide part with tab, and some with the bracket. This will give an area to attach the tab in the next step, and retain the needed lip for the bracket to rotate as it should
   
   
   
5. Next, you want to use some super glue and slide the tab into the slot in the back of the control panel as it would normally be, and slide it all the way towards the right (when viewed from behind) of the slot (as if the knob were being positioned to the left side for 'dash and feet' selection). There is another micro switch on the other side of the bracket's travel, however I am not exactly sure what that does.
   
   
   
   
   
6. You can now put the black bracket back on. Put the bottom part back on first, then tilt it on. You will see there is a key in the gear that will have to line up with the teeth on the bracket. You should be able to easily line it up, and then when it is back on, just rotate it back and forth full travel to verify.
   
   
7. Reinstall the control panel in the dash, making sure to reconnect the cables and electrical connectors they way you removed them. and now you should be able to turn on the blower, and with the re-circulation button selected, it will stay in recirc mode in any and all vent position selections. You can verify this by opening your glove box, dropping it down so you can see the HVAC air box behind it. look up a bit and you should see a grate or opening. With power on, when you turn on and off re-circulation mode, you can see a flapper door move inside. When it is covering that grate you can see, it is pulling in outside air. You will now see it will stay extended, that is, covering up the outside air opening, always pulling in air from behind the glove box and recirculating it.
   

 

[rshadd]

Nice write-up. Thanks for sharing.

 

[mdmartin]

Afterwards, I realized that the micro switch on the other side of the slot that this tab would hit when the knob was rotated to either defrost position, is used to turn on the A/C compressor (although it does not light the little light on the A/C button that it is on). So this mod also prevents the A/C compressor from being turned on when in either of the defrost vent positions, but it could still be turned on if desired with the A/C button.