DCrz38

Hi guys, long time lurker but first time poster. I have a really odd issue with my zed - I've scoured the Internet and it appears to be quite a unique problem, hoping someone might have some advice! Basically, when it's warm and sunny and the cabin is really hot, when I turn the AC on, the speedo goes crazy and bounces around all over the place. The digital speedo does the same, so I don't think it's to do with the cluster. This only happens when the car is at a standstill, as soon as I start moving a few mph then it's fine. Something that makes this even more weird - when the AC is on the windscreen (nob turned as far right) then it doesn't do it at all. As I turn the nob left, it gets progressively worse - so when it's pointed to feet and windscreen, it'll fluctuate between 0-10mph, when it's just on feet then 0-30mph etc., then when it's pointed at your face the digital speedo sits at 260mph and the cluster speedo appears to be at a rave. When the blower is on but not the AC, then there is no issue. The car is an '03 Jap import and has been converted from kmh to mph. Hoping someone could shed some light before I start replacing parts! Cheers