I dug into the climate control unit today. My car had some of the early symptoms of the “leaky Caps” problem. It’s an interesting circuit board. The main part is an Oki version of an Intel microcontroller. Most of the rest of the circuitry is simply to read the various temperature sensors. It looked like Honda even built their own analog to digital converter out of discrete transistors. An interesting engineering choice given the large number of A/D converters all packaged up in one IC – things must have been different in the late 80’s.
I think the problem with the capacitor leaking is that the gunk coming out of the capacitors messes up the A/D converter and the microcontroller reads all sensors as lower resistance. This has to make the firmware think everything is hot and cranks out the A/C on high. I’m very interested in why the capacitors are leaking. They are all high quality and rated at extra high temperature – 105 degrees C. In fact most capacitors that you can buy at Radio Shack are at the standard temp rating of 85 deg C. If heat is causing the leakage, the retrofitted boards should fail faster than the original ones.
Bottom line is that I think that I made it better by cleaning out the gunk and replacing the couple of leaking caps, but I think a new controller board is in my future.
I think the problem with the capacitor leaking is that the gunk coming out of the capacitors messes up the A/D converter and the microcontroller reads all sensors as lower resistance. This has to make the firmware think everything is hot and cranks out the A/C on high. I’m very interested in why the capacitors are leaking. They are all high quality and rated at extra high temperature – 105 degrees C. In fact most capacitors that you can buy at Radio Shack are at the standard temp rating of 85 deg C. If heat is causing the leakage, the retrofitted boards should fail faster than the original ones.
Bottom line is that I think that I made it better by cleaning out the gunk and replacing the couple of leaking caps, but I think a new controller board is in my future.
