C68 Electronic Climate AC Controller
You can find parts to complete the repairs below Click Here
You can find documentation on bench testing the controller Click Here
A free video of these repairs: Click Here
Disassemble the C68 Head Unit
Remove the two black metal clips holding the faceplate to the plastic housing.
Using a flat screwdriver, gently pry the tabs on the sides of the plastic housing which hold the main board.
Press on the green connector. This should cause the board and faceplate to slide out the front of the plastic housing.
Pull the faceplate away from the main board.
Replacing the Bulbs
Twist the three bulbs shown in the image above about 1/16 turn counterclockwise, then pull the bulb and socket out of the faceplate.
Carefully pull the bulb out of the socket.
Make sure the wires on the new bulbs are pointing straight, then insert them into the sockets.
Insert the sockets with the new bulbs into the three holes in the faceplate, then turn each approx 1/16 turn clockwise.
Rebuilding the C68 Head Unit
Using the technique of your choice, remove the two capacitors shown in the photo above.
If there's an electrolytic capacitor on the back of the wiring harness connector, remove it, too.
Replace the capacitors as shown in the photo above. Make sure to note the polarity markings on the capacitors and make sure they match the markings on the board.
Inspect the large blue power resistor solder joints, and resolder if they look cold or corroded.
Reinstall the board in the head unit housing, then reinstall the faceplate and reinstall the two metal clips.
Rebuilding the C68 Programmer Module
1) Remove the 1/4" nut holding the long bolt in the vacuum line block.
2) Remove the 1/4" screws holding the circuit board into the programmer housing, then remove the board.
3) Remove the capacitor and the two resistors shown in the photo above.
4) Replace the capacitor and resistors as shown in the photos above. Make sure to note the polarity markings on the capacitor and make sure it matches the markings on the board.
Update 8/2018: We found that about one in 100 programmers have bad blend door drive transistors. We have updated the kit to include replacement transistors (circled in red) and diodes (circled in yellow).
5) Replace both transistors circled in red in the photos below, making sure to face the flat side of the transistor faces the way shown in the photos below.
6) Next, replace both diodes circled in yellow in the photos below. Make sure the silver band painted onto the diodes face to the left as shown in the photos below when the board is oriented as shown below.
7) Reinstall the board in the housing, and reinstall the long bolt in the valve block.
Rebuilding the C68 Head Unit (Advanced - Board Connector Repair)
The most common problem with the C68 AC control unit is the connector that connects the face plate to the motherboard. Over time, pressure from the contacts in the connector causes the weak plastic housing of the controller to spread apart. Eventually, the contacts lose connection, and the C68 stops working or becomes intermittent.
Figure 1 - The problem connector
There are a few ways to deal with this:
Take it apart and clean the connections between the face plate and the motherboard. This only works for so long.
Heat the plastic connector, and bend it back into shape. It's easy to damage the factory connector, and again, this only works for so long before the problem comes back.
Remove the factory connector, and wire the faceplate to the motherboard. This is the only permanent way to fix the C68 controller, and that's the solution I'll present here.
Tools and Supplies Required
A small flat-bladed screwdriver
An Xacto knife
18-22ga wire - at least 8ft, and multiple colors are preferred.
A soldering iron, 25-40W
60/40 Tin/Lead rosin core solder (don't use acid core or lead-free solder on this component!!!
Desoldering braid, or a desoldering method of your choice
Thick Super glue to reattach the faceplate
Hot Glue Gun or Silicone Glue to secure wires to boards
For C68 Wiring and Troubleshooting info, Click Here
The batee.com Repair Procedure
Replacing the connector won't work. The problem is in the design of the particular card edge connector GM chose, and even if we could find a replacement, the problem would return over time. The solution involves removing the factory connector and replacing it with 16 short pieces of wire.
Warning! - This solution involves removing the faceplate from the faceplate circuit board. This means cutting 20+ melted plastic "rivets" in such a way that we can reattach the face plate later. But don't worry - it isn't difficult, and if you mess this up, replacement faceplate kits are available.
Disassemble the C68
- Remove the two black metal clips holding the faceplate to the plastic housing.
- Using a flat screwdriver, gently pry the tabs on the sides of the plastic housing which hold the main board.
- Press on the green connector. This should cause the board and faceplate to slide out the front of the plastic housing.
- Pull the faceplate away from the main board.
- Using the Xacto knife, slowly trim away the head (melted part) of the plastic rivets which attach the faceplate front to the faceplate circuit board. Leave the plastic posts sticking out the top of the circuit board so that they can be glued later. Be very careful not to break these posts, as they hold the buttons in proper alignment. The technique I used is to slide the blade of the Xacto knife under the head of the rivet, and gently pry up, breaking the thinner portion of the plastic rivet head away from the center plastic cylinder of the rivet. Be careful not to scratch the circuit board traces.
- Once all the rivets have been reduced to posts which fit through the holes in the circuit board, turn the panel so the buttons are face-down and lift off the circuit board. Set the faceplate and buttons aside. Be very careful with the faceplate circuit board, as the display is a glass vacuum tube which is very fragile.
- Using the method of your choice, desolder the 16 electrical connections which hold the white connector to the faceplate circuit board. Remove left over solder from the holes using desoldering braid.
Using a drill or needlenose pliers or whatever method you choose, remove the two rivets which physically hold the white connector to the faceplate circuit board.
Figure 2 - White Connector Removed
Cut 16 segments of 18-22ga wire in 6-8" lengths, then strip and tin both ends of each wire. Be sure to use stranded wire, as solid wire will break over time due to vibration.
Solder one end of each of the 16 wires to the contacts on the faceplate circuit board, with the wire protruding out the back side of the circuit board (the side opposite the glass display.
Figure 3 - Wires attached to faceplate circuit board
Figure 4 - Note the "1" markings on each board, and connect the wires accordingly!
Note the "1" markings at one end of the holes in the faceplate circuit board and the "1" marking at the end of the card edge connector of the main board. Make sure to solder pin 1 on the faceplate to pin 1 on the main board. Repeat for the next 15 wires.
Figure 5 - Wires attached
Before reassembly, consider bench testing the C68. Use your Digital Cluster cable (or the techniques in this article to build one). Connect ground to pins C7 and C8 of the green external connector on the C68. Connect C2 and D4 to +12V. It should power up as shown below. Push a few buttons to be sure it's working. Don't worry, the low voltage won't injure you.
For C68 Wiring and Troubleshooting info, Click Here
Figure 6 - Wires attached
Make sure the bulb holders are in place to cover the bare traces needed for illumination. Then using Hot Glue or Silicone glue, apply glue over the wires and onto the circuit board to act as a strain relief. Stay away from the bulb holders so that the bulbs can be replaced if needed.
Figure 7 - Strain Relief
Figure 8 - More strain relief
Make sure the buttons are properly seated in the faceplate, then place the grey rubber pads over the plastic posts in the faceplate, as shown in Figure 9.
Figure 9 - positioning the grey pads
Press the faceplate circuit board onto the plastic posts of the faceplate. Apply some electrical tape as shown in Fig 10 to temporarily hold the faceplate together.
Figure 10 - Reattaching the Faceplate
Test the button functionality again. When you're confident that everything is aligned properly and functioning, proceed to the next step.
Apply a small drop of thick superglue (sometimes called Gel Superglue) to the head of each plastic post. Let dry thoroughly before removing the electrical tape.
Reassemble the unit: Install the main board into the plastic housing until it locks into place. Then place the faceplate into the plastic housing. Finally, reinstall the two metal clips which hold the faceplate to the plastic housing.
Figure 11 - Reassembled and Working!