I have a 2000 Si, With my stock obd-2 computer in the car my A/C works; when I plug in my jumper harness and p28 (tuned on crome) it doesn't work.

P28 plugged in
-A/C interior led illuminates
-no juice at the A/C compressor relay
-no juice at the Pressure switch (tried jumpering the switch)

I am stumped; is there an issue with running A/C and having a P28 (crome) ecu?

Do I need to switch my engine management to maintain my A/C? I just reinstalled it and freshly charged it

When I run the stock ecu I get crappy as hell fuel mileage and the car feels really weak- I have a 2nd o2 code being thrown that's the only thing I could see causing the craptastic FM- Besides I have a mildly worked over motor and don't wish to run the stock ecu.

 

Sounds like the output on the P28 isn't working. Try another P28.

 

Is it a specific diode or a component I can measure? I do regular work with oscopes if anyone has a board schematic it would be great. Thnx!

 

There's a schematic available on pgmfi.org

 

has anyone had this problem before and possibly have the componant I need to look at?