A/C Signal Circuit Troubleshooting

Turn the ignition switch OFF.
Disconnect the A/C pressure switch 2P connector.
Turn the ignition switch ON (II).
Measure voltage between PCM connector terminals A27 and B20.

Fig 1: Measuring Voltage Between PCM Connector Terminals A27 & B20
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there about 5 V or battery voltage?
1. YES -Go to step 5.
2. NO -Go to step 12.
Turn the ignition switch OFF.
Reconnect the A/C pressure switch 2P connector.
Turn the ignition switch ON (II).
Momentarily connect PCM connector terminals A17 and B20 with a jumper wire several times.

Fig 2: Connecting PCM Connector Terminals A17 & B20 With A Jumper Wire
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there a clicking noise from the A/C compressor clutch?
1. YES -Go to step 9.
2. NO -Go to step 15.
Start the engine.
Turn the blower switch ON.
Turn the A/C switch ON.
Does the A/C operate?
1. YES -The air conditioning signal is OK.
2. NO -Go to step 16.
Turn the ignition switch OFF.
Disconnect PCM connector A (32P).
Check for continuity between body ground and PCM connector terminal A27.

Fig 3: Checking For Continuity Between Body Ground & PCM Connector Terminal A27
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES -Repair short in the wire between the PCM (A27) and the A/C pressure switch.
2. NO -Substitute a known-good PCM and recheck (see HOW TO SUBSTITUTE THE PCM FOR TESTING ). If prescribed voltage is now available, replace the original PCM. If not, check the A/C system for other symptoms.
Momentarily connect under-hood fuse/relay box 16P connector terminal No. 11 to body ground with a jumper wire several times.

Fig 4: Connecting Under-Hood Fuse/Relay Box 16P Connector Terminal No. 11 To Body Ground With A Jumper Wire
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there a clicking noise from the A/C compressor clutch?
1. YES -Repair open in the wire between the PCM (A17) and the A/C clutch relay.
2. NO -Check the A/C system for other symptoms.
Measure voltage between PCM connector terminals A27 and B20.

Fig 5: Measuring Voltage Between PCM Connector Terminals A27 & B20
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there less than 1.0 V?
1. YES -Substitute a known-good PCM and recheck (see HOW TO SUBSTITUTE THE PCM FOR TESTING ). If the symptom/indication goes away, replace the original PCM. If not, inspect the air conditioning system.
2. NO -Repair open in the wire between the PCM (A27) and the A/C pressure switch.