The ACC on my 86-420SEL intermittently quits. I have added plenty of freon in the system...no bubbles in the site glass. The compressor works.The limit switches seem to work. No noticible leaks in the system. I think the problem could to be with either the temperature setting thumb-wheel or the push-button switches for the ACC. How do I remove the faciaplate around the ACC to test and clean the contacts on these items??