I bought an OBD-2b to OBD-1 conversion harness for a buddy of mine's 99 Si and everything works well except for the A/C. We thought it was the ECU itself (Stock P28). But we switched it out with another P28 (another stock one) still no luck. We then swapped it out with a P30 and still no A/C. It's some eBay conversion harness. I've bought one for another friend of mines car and the A/C works perfect. Do you guys think that he should just step up and get the Skunk2 one? Thanks guys.

 

It would probably help, it sounds like a wiring issue to me. I don't believe the ac is OBD specific in anyway as long as the harness is set up correctly for that cars particular wiring...