LEDs for the HVAC controls

[divestoclimb]

I know others have done this mod, but I thought I'd share my approach and some lessons learned.

Background
Behind the HVAC controls sit six bulbs in proprietary twist-lock bases: three 5mm bulbs to illuminate the dials and three 3mm bulbs for the lower three buttons (Recirc, A/C, rear defrost).

Remove the HVAC controls from the center console by removing the four screws holding them in place, then remove the four screws on the back side and pop the tabs out to remove the back of their plastic housing. Once you have done this you can rotate the PCB out, though it will remain attached to the rest of the unit via ribbon cables. I was unable to figure out how to disassemble the unit any further--it looks like there are screws on the front PCB's that are soldered in place.

For the upper bulbs I used #74 tri-star LED modules from superlumination.

1. Remove the existing bulbs from the upper twist-lock bases.
2. Cut the bases short.
3. Straighten the metal leads on each module, then solder really thin wires to the ends (or cut off and use the leads from the existing bulbs)
4. Since the tri-star modules won't fit through the hole in the PCB, you have to assemble the LED module to the base with the base already in the hole (see the pic below)
5. Secure the modules to the bases with hot glue.

I suggest using white for the middle dial since it has multiple colors on the face. I chose red for the left and right ones, but I do perceive a difference in brightness--the white one definitely is brighter, especially on the blue side of the temp. dial.

One more note--LED's, even these tri-stars with a decent projection angle, will not illuminate the little red dots on the edge of each dial. When it's completely dark it's difficult to see what each dial is set to.

[divestoclimb]

For the lower bulbs, I first tried the same T-1 LED's I used to replace my cruise control and power mirror bulbs, but they were too dim for this application. Unlike those other buttons, the HVAC control buttons are not sitting directly in front of the bulbs--instead, there is a white plastic piece that reflects the bulb's light onto the back of the buttons. Aluminum foil covering this plastic piece might do the trick, but I was unable to disassemble the controls any further than I described above.

My next attempt was T-1 super bright (2000mcd) red LED's from Action Electronics. The problem was that these LED's are not 12V-ready, so I had to add limit resistors. Since these bulbs with a 2.5V max forward drop and 25mA max current, I selected 470 Ohm 1/4 Watt resistors (I can explain the math upon request). I soldered the resistors to the LED leads after inserting them through the twist-lock bases, as pictured below. After I got it looking as pictured, I coated that rat's nest of wire with hot glue to keep it from shorting. Once assembled, these modules can then be inserted normally into the HVAC control box.

[ramblerdan]

Nice work, Dives. Thanks for the writeup.

[nathan5871]

Originally Posted by divestoclimb

For the lower bulbs, I first tried the same T-1 LED's I used to replace my cruise control and power mirror bulbs, but they were too dim for this application. Unlike those other buttons, the HVAC control buttons are not sitting directly in front of the bulbs--instead, there is a white plastic piece that reflects the bulb's light onto the back of the buttons. Aluminum foil covering this plastic piece might do the trick, but I was unable to disassemble the controls any further than I described above.

My next attempt was T-1 super bright (2000mcd) red LED's from Action Electronics. The problem was that these LED's are not 12V-ready, so I had to add limit resistors. Since these bulbs with a 2.5V max forward drop and 25mA max current, I selected 470 Ohm 1/4 Watt resistors (I can explain the math upon request). I soldered the resistors to the LED leads after inserting them through the twist-lock bases, as pictured below. After I got it looking as pictured, I coated that rat's nest of wire with hot glue to keep it from shorting. Once assembled, these modules can then be inserted normally into the HVAC control box.

I did my HVAC LED's the same exact way and had no problem. Great minds think alike I guess.

[divestoclimb]

I found a semi-reliable way to get the little red dot lit up again. To do it, I disassembled the dials (here's how) and removed the little clear plastic piece acting as a diffuser for the original bulb. In its place I hot-glued a 3mm red LED (it doesn't have to be high-power or anything).

I then took a section of some old Cat5 ethernet cable, cut off the outer sheath, and separated out the four twisted pairs. I soldered a pair onto each dial's LED leads and wrapped them around the gauges three times. I didn't do any experimentation with the ideal number of wraps, three just seemed to look right but it's possible more or fewer wraps would work better. Once I had the length right, I hot-glued the end to the dial base.

The tricky part is packing this cable reel into the HVAC control housing. If you don't do it right the wire can snag on all the little plastic pieces in there or wrap back on itself and jam. It's also possible for everything to work fine except the dial is difficult to turn. With patience and coaxing, it's possible to get the reel in there without having any effect on how the dial rotates. Once packed, I soldered the cable reel leads to the exposed leads on the dial face LED's for power.

I have also removed the plastic color filters from the buttons and left and right dial faces, it makes the gauges light up really well.

[JourneymanAcuraMech]

Dives,

Are you Sure?

Originally Posted by divestoclimb

it's possible to get the reel in there without having any effect on how the dial rotates

I've been playing with this for hours. It doesn't work.