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Air Conditioning Signal

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1999 Isuzu Oasis, 1998 Isuzu Oasis, 1998 Honda Prelude, 1998 Honda Odyssey, and 1998 Honda Civic. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: This signal informs the PCM that there is a demand for cooling from the A/C system.
  1. Turn ignition off. Disconnect A/C pressure switch (all models) and A/C diode (Civic, Oasis, Odyssey & Prelude). See A/C SIGNAL COMPONENT LOCATIONS  . Turn ignition on. Measure voltage between PCM connector terminals A27 and B20 (Accord, Oasis & Odyssey) or terminals A9 and C5 (Civic, CR-V & Prelude). See Figure . If 5 volts exists (battery voltage on CR-V & Prelude), go to next step. If specified voltage does not exist, go to step 4).
  2. Turn ignition off. Reconnect A/C pressure switch (all models) and A/C diode (Oasis, Odyssey & Prelude) connectors. Turn ignition on. Using a fused jumper wire, momentarily connect PCM connector terminals A17 and B20 (Accord, Oasis & Odyssey) or terminals A9 and A17 (Civic, CR-V, Oasis & Odyssey), several times. See Figure . If A/C compressor clutch makes a clicking sound, go to next step. If A/C compressor clutch does not make a clicking sound, go to step 5).
  3. Start engine. Turn A/C and blower motor switches on. If A/C operates, A/C signal is okay. If A/C does not operate, go to step6. 4)Turn ignition switch off. Disconnect the PCM connector A (Accord, Oasis & Odyssey), C (Civic, CR-V & Prelude). Check for continuity between ground and terminals A27 (Accord, Oasis & Odyssey) or C5 (Civic, CR-V & Prelude). If continuity does not exist then substitute a known-good PCM then recheck for voltage. Repeat step 1). If continuity exists, then repair short in wire between A27 or C5 and A/C pressure switch. If specified voltage now exists, replace original PCM. If specified voltage still does not exist, inspect A/C system. Refer to appropriate A/C - HEATER SYSTEM article in the AIR CONDITIONING & HEAT section.
  4. Using a fused jumper wire, momentarily connect under-hood fuse/relay box 16-pin connector terminal No. 11 (Accord) or under-hood fuse/relay box 9-pin connector terminal No. 5 (Civic & CR-V) or A/C clutch relay connector terminal No. 4 (Oasis, Odyssey & Prelude)to ground several times. to ground several times. See Fig 1 & 6. See A/C SIGNAL COMPONENT LOCATIONS  . If A/C compressor clutch makes a clicking sound, repair open in wire between A/C clutch relay and PCM connector terminal A17 (all models). See WIRING DIAGRAMS article. If A/C compressor clutch does not make a clicking sound, inspect A/C system. Refer to appropriate A/C - HEATER SYSTEM article in the AIR CONDITIONING & HEAT section.
  5. Turn ignition off. Disconnect PCM connectors "A" and "B" (Accord, Oasis & Odyssey) or "A" and "C" (Civic, CR-V & Prelude). Measure voltage between terminals A27 and B20 (Accord, Oasis & Odyssey) or A9 and C5 (Civic, CR-V & Prelude). If there is less that 1 volt measured, then substitute a known-good PCM then recheck for voltage. If specified voltage now exists, replace original PCM. If specified voltage still does not exist, inspect A/C system. Refer to appropriate A/C - HEATER SYSTEM article in the AIR CONDITIONING & HEAT section.
A/C SIGNAL COMPONENT LOCATIONS

A/C Component Location
Accord
Clutch Relay Under-hood fuse/relay box.
Pressure Switch On Receiver/Dryer at right front corner of condenser.
Civic
Clutch Relay Under-hood fuse/relay box.
Diode Under-hood fuse/relay box.
Pressure Switch On Receiver/Dryer at left front corner of engine compartment, next to power steering fluid reservoir.
CR-V
Clutch Relay Under-hood fuse/relay box.
Pressure Switch On Receiver/Dryer at left front corner of engine compartment, next to power steering fluid reservoir.
Oasis & Odyssey
Clutch Relay Under-hood fuse/relay box.
Pressure Switch On Receiver/Dryer at right front corner of condenser.
Prelude
Clutch Relay Left front corner of engine compartment.
Diode Left front of passenger's footwell under middle of instrument panel.
Pressure Switch On Receiver/Dryer at right front corner of condenser.
Fig 1: Identifying A/C Clutch Signal Testing Connectors
G98H07142Courtesy of AMERICAN HONDA MOTOR CO., INC.
Fig 2: Identifying A/C Clutch Relay Connectors
G98J07143Courtesy of AMERICAN HONDA MOTOR CO., INC.
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