A/C Switch Input Test

Fig. 23 System checker harness terminal identification:

1988 Prelude
1. Connect system checker harness between ECU and connector, Fig. 23, but disconnect B connector from engine compartment wiring harness only, not the ECU.
2. Turn ignition switch to On position and measure voltage between B8 (+) terminal and A18 (-) terminal.
3. If there is not approximately 5 volts, substitute a known good ECU and repeat test and, if approximately 5 volts is now available, replace original ECU.
4. If there is approximately 5 volts, reconnect B connector to engine compartment wiring harness and connect B1 terminal to A18 terminal.
5. If A/C operates, proceed to step 9.
6. If A/C does not operate, connect red/blue terminal of 13 pin connector on compressor control unit to body ground.
7. If A/C does not operate, trouble is in A/C system.
8. If A/C operates, repair open in red/blue wire between ECU B1 terminal and compressor control unit.
9. If A/C operated in step 5, start engine and turn blower and A/C switches on.
10. If A/C does not operate, problem is in A/C system.
11. If A/C operates, measure voltage between B8 (+) terminal and A18 (-) terminal.
12. If voltage is not below 1 volt, repair open in red/green wire between ECU B8 terminal and A/C switch.