100 Series Button Repair How-To - A/C, Defrost, Recirc etc (1 Viewer)

[metty]

April 2020 edit - after 18 months, everything is still working great!

Edit - Its been about 5 weeks of daily driving since i did this and all the buttons are still working great!

Hi All,

I have taken tons of valuable info from this site and now it is my turn to contribute something.

This write up covers the repair of the buttons shown below for the recirculation, A/C, defrost and rear controls:

On my cruiser, all of these buttons were getting to be really intermittent and over the past month it had gotten to where i could not reliably turn off the A/C or the rear controls.

I took apart the panel to see what the issue was - the blue button shown below is the heart of the issue, these are some kind of conductive silicone switch that over time will build up corrosion on the contacts and either not work at all or work very intermittently:

Switch guts, the small black dot on the right is conductive silicone and the two contacts shown on the left are the switch contacts; when the switch is depressed, the silicone is supposed to complete the circuit

Now, the repair procedure

• Disconnect the battery
• Remove the switch panel/radio surround by carefully prying it out of the dash. There are maybe 8 or so clips around the outside that have to release
• Unplug the 4 large multipin connectors from the back of the panel and take it to the bench
• Remove the knobs from the front by gently prying them up

• Remove the nuts and washers from the rotary switches with an 11mm socket (in the image above they have already been removed)
• Flip the assembly over and remove the screws that hold the black plastic panel on the back
• Once you have removed the visible screws, carefully pull the black plastic cover to the side and remove the other screws that hold the PCBs down

continued on next post

 

[metty]

• Remove this screw as well

• Once you have removed these screws, carefully separate the circuit boards and the black plastic cover assembly from the front panel and lay the assembly out on the bench. You can unplug the small harness with the red wires to make this easier on yourself and separate the two main parts of the assembly

• Remove the small black plastic switch covers from each switch

• Now, this is where it gets tricky and it helps to have a desolder station
• Carefully scrape off the conformal coat (clear goo) from the switch contacts to be desoldered

• Using solder wick or a solder sucker, carefully desolder the switch from the board and remove it

 

[metty]

• With the old switch removed, use your solder removal device and clean up the thru holes in the board
• Insert the new switch in the board

• Be careful to ensure that the switch is fully seated against the PCB, if the spacing is wrong you run the risk of the button being depressed all the time when the panel is reassembled
• Carefully solder the new switch in place
• Rinse and repeat for the remaining switches

For the A/C and Recirc switches, there are a few extra steps

• Remove the screws as shown below

• These two screws hold the white plastic surround (shown below) to the PCB

• Once the screws are out, you can carefully pull the white plastic surround off
• Note, now is a good time to replace any backlight bulbs that are burned out, i think these are all T4 size
• With the plastic surround removed, repeat the same switch replacement procedure as before on the A/C and recirc switches
• Plug the harness with the red wires back in and carefully reassemble the whole panel
• I dont have a good picture of it, but the small PCB that has the hazard and CDL switches can be a pain, the buttons on the front of the panel have to "snap" on to the switches or you wont be able to actuate them when it is all reassembled
• Put the panel back in and test out your new buttons!

 

[metty]

I probably should have listed this first, but here is some info on replacement switches:

• The existing switches are ~5.2mm tall with lead spacing of ~5mm. This lead spacing works out to a very common size for thru hole components which is 0.200", there are many options on digikey, newark etc
• The height is very critical for the buttons to work correctly, i found that a switch with a height of 5mm works perfectly such as the one below
• I like the feel of a tactile switch that actually clicks when you push it which is why i went with this over the original switches
• Note that the switches you need are normally open momentary switches, i.e. when you push the switch down it makes contact until you release it, at which point it opens the switch again. The latching logic is handled in the microcontroller on the PCB
• These switches were $0.16 each the last time i looked on Newark FYI

https://www.newark.com/alcoswitch-t...t/switch-tactile-spst-50ma-through/dp/14H0928

• Comparison of old and new switches

 

[metty]

one last photo showing height of stock switch

 

[YardPig]

Excellent writeup. Someone should offer this service, I too have run into this issue before...​

 

[TLCJC]

My 1999 LX side mirror Defog and rear AC switches are starting to go.

How long does this procedure take for each switch?

This seems a bunch of rings too high for novice level...

Thanks for the detailed HI TECH write up!

 

[mmaakk]

Seems it could be a chronic issue, my 99 is having the same symptoms. Defrosts and rear AC. Pain in the ass! Have to hit the switches 3-5 times for them to activate at times. Wonder if it’s the same issue for the center lock...?

 

[metty]

My 1999 LX side mirror Defog and rear AC switches are starting to go.

How long does this procedure take for each switch?

This seems a bunch of rings too high for novice level...

Thanks for the detailed HI TECH write up!

Yeah, if you have not done electronics repair before its probably 2-3 bananas

Once you have it out on the bench it takes no more than 5 minutes per switch. Overall time from start to finish including removing/installing/testing was about an hour for me but i have a pretty nice desolder station to work with

Seems it could be a chronic issue, my 99 is having the same symptoms. Defrosts and rear AC. Pain in the ass! Have to hit the switches 3-5 times for them to activate at times. Wonder if it’s the same issue for the center lock...?

The CDL switch is a different type of switch entirely (latching pushbutton) and i dont think it suffers from the same failure mode

 

[neckbone]

Great writeup, and very detailed pictures. My '99 LX is having the same issues. Have to press a few times and having to press harder each time. Unfortunately, I never knew the term desolder, so I think this is a bit out of my wheelhouse (3rd time I've used that word in two days, YAY!!)

If you're bored over Christmas, swing on down to Columbia, SC and I'll feed you some Natty's and do a little circus dance for payment on fixing mine. HAHAHA!!

 

[cruzerDave]

one last photo showing height of stock switch
View attachment 1856758

You are awesome! THANK YOU for showing me how to fix one of my biggest minor annoyances with my truck (the rear heater switch). Please PM me with your address and a Chum Bucket will be on its way...

 

[gee314]

This is AWESOME! My recirculation and A/C are so frustrating. I've been trying to figure out how to fix this!
Thanks!!

 

[thetoyotaman]

Thanks for posting this! Just replaced some dash bulbs in my 03 LX and those look like the same buttons. My rear fan button is starting to get stubborn. There are also bulb assemblies that look like that size that I was able to change the bulb in but would be nice to have a source.

 

[gee314]

I replaced the buttons behind my climate control a few weeks ago using this thread. I didn't actually have to remove the knobs to do it.

Also, I forgot to plug back in the circuit board that manages the center diff and hazards. I found this out when I used low range. The center diff locked, but would not unlock. I assume this is because upon shifting out of low range the computer "checks" in with the center diff switch. Since it was not plugged in, the computer decided it should not be unlocked. I took everything back apart and found forgotten plug. Now it works fine.

 

[TLCJC]

Yeah, if you have not done electronics repair before its probably 2-3 bananas

Once you have it out on the bench it takes no more than 5 minutes per switch. Overall time from start to finish including removing/installing/testing was about an hour for me but i have a pretty nice desolder station to work with



The CDL switch is a different type of switch entirely (latching pushbutton) and i dont think it suffers from the same failure mode

Do you have some photos of your desolder station to share?

 

[gee314]

Do you have some photos of your desolder station to share?

I used something like this: Aven Desoldering Pump with ESD Safe Plastic-17536 - The Home Depot

 

[metty]

This is what i have at work but it is way out of reach of the home shop:

JBC Rework Station

Something like gee314 posted will work well for this type of repair

 

[Ayune]

Solder wick is the best cheap way of removing excess solder from a joint. Place the wick on the cold joint, then the iron on top of the wick. The solder will be sucked up the wick. Cut off the used portion of the wick and repeat if necessary.

NTE Electronics SW02-10 No-Clean Solder Wick, 4 Blue.098" Width, 10' Length: Amazon.com: Gateway

NTE Electronics SW02-10 No-Clean Solder Wick, 4 Blue.098" Width, 10' Length: Amazon.com: Gateway

www.amazon.com

How-to video:

 

[gee314]

Solder wick is the best cheap way of removing excess solder from a joint. Place the wick on the cold joint, then the iron on top of the wick. The solder will be sucked up the wick. Cut off the used portion of the wick and repeat if necessary.

NTE Electronics SW02-10 No-Clean Solder Wick, 4 Blue.098" Width, 10' Length: Amazon.com: Gateway

NTE Electronics SW02-10 No-Clean Solder Wick, 4 Blue.098" Width, 10' Length: Amazon.com: Gateway

www.amazon.com

I tried a wick, but found the pump a bit easier to use. Either would work though.

 

[Ambledog]

I was looking for something just like this! Thank you so much. I've been fighting these dang buttons since I got the LC but never really pulled things apart to look at those switches.