1986-1989 C68 Electronic Climate Control Repair Guide
C68 Electronic Climate AC Controller
You can find parts to complete the repairs Click Here
You can find documentation on bench testing the controller Click Here
Disassemble the C68 Head Unit
1) Remove the two black metal clips holding the faceplate to the plastic housing.
2) Using a flat screwdriver, gently pry the tabs on the sides of the plastic housing which hold the main board.
3) Press on the green connector. This should cause the board and faceplate to slide out the front of the plastic housing.
4) Pull the faceplate away from the main board.
Replacing the Bulbs
5) Twist the three bulbs shown in the image above about 1/16 turn counterclockwise, then pull the bulb and socket out of the faceplate.
6) Carefully pull the bulb out of the socket.
7) Make sure the wires on the new bulbs are pointing straight, then insert them into the sockets.
8) 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
9) Using the technique of your choice, remove the two capacitors circled in red in the photos above.
10) If there's an electrolytic capacitor on the back of the wiring harness connector, remove it and replace it with one of the large capacitors supplied in the kit. Note that the positive terminal is soldered to terminal D4 and the negative terminal is connected to Terminals D12 and D13 of the wiring harness connector. See photo below. The rear capacitor is shown circled in blue. Note the bends in the capacitor leads, shown below.
11) Replace the capacitors as shown in the photo below. Make sure to note the polarity markings on the capacitors and make sure they match the markings on the board.
12) Inspect the large blue power resistor solder joints shown circled in orange, and resolder if they look cold or corroded.
13) We have seen a case where the blower motor would not run, even though the wiring, the blower motor, the fuse and the blower control module are all good. The symptom was that the voltage on pin C3 of the controller remains at or near zero when the fan speed changes from 1 to 2 all the way up to 10, and the voltage across the blower motor terminals remains 0 (it should be 4-12V), andd the voltage across the small cap remains at 0. The solution was to replace the 12 Ohm resistor which supplies power to the switching voltage regulator circuit that generates the 5.8V voltage which appears across the smaller capacitor. The resistor is color coded Brown Red Black Gold, and the location on the top side of the main logic board is shown circled in yellow in the photo below. It's super-easy to find, as there's only one 12 Ohm resistor on the logic board! Remove the old resistor and install the new one. Polarity doesn't matter here.
14) Reinstall the board in the head unit housing, then reinstall the faceplate and reinstall the two metal clips.
Rebuilding the C68 Programmer Module
15) Remove the 1/4" nut holding the long bolt in the vacuum line block.
16) Remove the 1/4" screws holding the circuit board into the programmer housing, then remove the board.
17) Remove the capacitor and the two resistors shown in the photo above.
18) 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).
19) 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.
20) 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.
21) Reinstall the board in the housing, and reinstall the long bolt in the valve block.
Stop Here and test your controller. If it's working, stop here! If the display or one or more switches isn't working, then continue to the next part.
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
Possibly a replacement faceplate kit Click Here
For C68 Wiring and Troubleshooting info, Click Here
The batee.com Repair Procedure
Replacing the connector won't work. They're not available so far as I know, and 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 first solution involves heating and reshaping the connector. This won't work if your connector contacts are mangled or have been overheated by a short circuit, but it is the least invasive way to fix connectivity issues.
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. Don't worry - it isn't difficult, and if it isn't possible to reattach the old faceplate plastic, replacement faceplate kits are available.
Disassemble the C68
22) Remove the two black metal clips holding the faceplate to the plastic housing.
23) Using a flat screwdriver, gently pry the tabs on the sides of the plastic housing which hold the main board.
24) Press on the green connector. This should cause the board and faceplate to slide out the front of the plastic housing.
25) Pull the faceplate away from the main board.
26) Using the Xacto knife or side cutters, 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.
27) 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.
28) As of 1/2019, we're updating the kit to include the 10 LEDs on the faceplate circuit board. If you had problems with one or more of these not lighting when it should consider replacing it. Be sure to solder the LED at the same height all the others solder in. Be sure to solder the long lead of the LED into the hole marked + on the board. LED locations are shown circled in purple in Figure 6 below.
Figure 6 - LED Locations
29) Before reassembly, consider bench testing the C68. 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.
30) 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.
31) Heat the connector with a heat gun. We use a 250W heat gun, not one of the big 1000W paint stripper heat guns! The purpose of this is to soften the plastic. The connector will gradually pull itself straight again.
Once the plastic softens, use a straight edge and press it up against the side of the connector to make sure it's absolutely straight.
32) Resolder the 16 connections to the faceplate. Also resolder the connections where the display pins meet the faceplate circuit board.
33) Clean the display with windex.
34) Clean the switch contacts with isopropyl alcohol and a paper towel or Q-tip.
35) 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 10.
Figure 10 - positioning the grey pads
36) Press the faceplate circuit board onto the plastic posts of the faceplate. Apply some electrical tape as shown in Fig 11 to temporarily hold the faceplate together.
37) Test the button functionality again. When you're confident that everything is aligned properly and functioning, proceed to the next step.
38) 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.
39) 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 12 - Reassembled and Working!
Warning: Only use this next procedure if your 16 connector is broken or melted beyond use!
40) 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
41) 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.
42) 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: Apply some solder to each pad on the main logic board
43) 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
44) If you're experiencing display problems, resolder all the solder joints where the display connects to the faceplate PC board. Do this on both sides of each pin.
For C68 Wiring and Troubleshooting info, Click Here
Figure 7 - Wires attached
45) 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 8 - Strain Relief
Figure 9 - More strain relief
46) 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 10.
Figure 10 - positioning the grey pads
47) Press the faceplate circuit board onto the plastic posts of the faceplate. Apply some electrical tape as shown in Fig 11 to temporarily hold the faceplate together.
Figure 11 - Reattaching the Faceplate
48) Test the button functionality again. When you're confident that everything is aligned properly and functioning, proceed to the next step.
49) 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.
50) 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 12 - Reassembled and Working!