Ok I hope someone on here can help me with this problem. I have a 2000 Civic SI with a B16a SIRII motor swapped in. I have the original OBD2b harness that plugs into my jumper harness and terminates at the P30 ECU. My problem is the AC clutch will not engage. Now this is what I have done:
Checked all fuses according to the troubleshooting section of the factory manual. Verified my Compressor clutch relay is working. Checked for continuity between Underhood fuse box and A17 and A15(obd2b to obd1 pinout for ACC signal) My condenser fan kicks on and stays on when the AC button and fan are turnded on. My pressure switch is closed indicating good pressure. I also put a Freon gage and it looks good. I jumpered pins 1 and 2 of the compressor clutch relay socket and I can here the compressor clutch click. I checked for continuity from the relay socket to the compressor clutch connector. Here's the weird part. When an OBD2b computer is plugged in the AC works fine. Blows ice cold air. So I looked in the schematics. I found that on a stock computer setup the a NPN transistor switches a ground connection and that engages the coil on the ACC relay. If you look at a OBD1 schematic from a 92-95 civic, It looks like the ACC gets it's ground from a double pole Ac Switch. So does that mean the obd1 is incapable of shunting my ACC ground to complete the circuit? Any suggestions out there. I guess I'm not the only one who's done this to their car.

 

Ok for anyone out there who will have or has had this problem. I found the ground comes from the AC switch for the OBD1 computer. Because my wiring harness is looking for the ground at the OBD2B ECU, my clutch never kicks in. I'm going to re-wire my ac system just like the obd1 civic. If anyone needs help just message me I can provide schematics and instructions on how to rewire the system.

 

I have a problem with my obd1 a/c circuitery, the npn transistor is always supplying ground to the clutch relay. I can't find an spare transistor qm3, but i got the datasheet, but I can't understand the function of the avalanche diode, also there's not spec for the diode. I need to see your rewire so i can fix or build a transistor.

Thanks

 

Why not just replace the ECU?

 

would it be possible for you to share those schematics? im a decade late but i am having the exact same issue.

 

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