Hoping someone here can help me figure out what's going on. I've spent a lot of time diagnosing this and I'm at the point where I need other eyes on it before I pull the ECU again or take it to a tuner.
Setup:
- 1999 Honda Accord, F23A engine
- OBD2B-to-OBD1 conversion using Speed Factory conversion harness
- P28 ECU (Denshigiken PCB, standard factory board)
- S300 V3, firmware version 24
- SManager 2.8.9.0 (up to date, update option greyed out)
A/C clutch and radiator fan won't engage when A/C is requested. ECU is not commanding ACCL output (A15 stays at battery voltage with A/C button pressed, engine running). SManager is not registering ACSW turning on even though B5 has a clean signal.
What I've tested:
1. Hardware side is good:
- Swapped relays, no change
- Jumpered AC relay directly - clutch engages and both rad fans turn on. Clutch coil, pressure switch, wiring, and fan circuits are all functional.
- Recently replaced compressor (Denso OEM), TXV, and receiver/drier. Full 22.9oz charge.
- 4.7V with A/C off (DC, key on)
- 0.02V with A/C button pressed and pressure switch closed (DC, engine running)
- Conversion harness routes A27 (F23A ACS) to B5 (P28 ACSW) correctly
- ACSW parameter visible in sensor readouts, stays OFF no matter what
- Grounding B5 directly at the ECU connector with a jumper also does NOT toggle ACSW
- ACCL output works when manually commanded via output test (clutch engages)
- PSPSW (B8) toggles correctly in SManager when the wheel is turned
- This tells me the S300 and SManager CAN read switch inputs on this ECU
- No DTCs stored
- Shop set up the S300 for P28 at time of purchase
- Misc > Air Conditioning only shows two settings: cutoff at 5000 RPM and cutoff above 36% throttle
- I don't see a dedicated A/C Control section or any ACSW enable/disable option
Given that B5 has a clean 5V to 0V signal, PSPSW works fine (proving switch inputs can be read), and ACCL output works when manually commanded, what would cause ACSW specifically to not register? Is this a known issue with firmware 24 or SManager 2.8.9.0? Is there a calibration setting I'm missing? Or should I suspect a hardware fault on the B5 input path specifically?
Anyone run into this before on a P28/F23 swap setup? Happy to upload my .skl file or post photos of the S300 board if it helps.
Thanks in advance