Skip to main content
A/C Pressure Switch Circuit Troubleshooting

NOTE:
  • Do not use this troubleshooting procedure if any of these items are working properly with the A/C switch ON; condenser fan, radiator fan, A/C compressor, or if the heater does not work. Refer to the symptom troubleshooting index.
  • Check the A/C high-side pressure.
  1. Disconnect the A/C pressure switch 2P connector.
  1. Turn the ignition switch to ON (II).
  1. Measure the voltage between the A/C pressure switch 2P connector No. 2 terminal and body ground.
Is there battery voltage?
YES -
Go to Step 4 .
NO -
Go to Step 23 .
  1. Turn the ignition switch to LOCK (0).

  1. Check for continuity between the No. 1 and No. 2 terminals of the A/C pressure switch.
Is there continuity?
YES -
Go to Step 6 .
NO -
Replace the A/C pressure switch.■
  1. Reconnect the A/C pressure switch 2P connector.
  1. Disconnect the A/C switch 5P connector.
  1. Turn the ignition switch to ON (II).

  1. Measure the voltage between the A/C switch 5P connector No. 2 terminal and body ground.
Is there battery voltage?
YES -
Go to Step 10 .
NO -
Repair open in the wire between the A/C pressure switch and the A/C switch.■
  1. Turn the ignition switch to LOCK (0).
Is the A/C switch OK?
YES -
Go to Step 12 .
NO -
Replace the A/C switch.■
  1. Disconnect the heater fan switch 8P connector.

  1. Check for continuity between the A/C switch 5P connector No. 1 terminal and the heater fan switch 8P connector No. 6 terminal.
Is there continuity?
YES -
Go to Step 14 .
NO -
Repair open in the wire between the A/C switch and the heater fan switch.■
Is the heater fan switch OK?
YES -
Go to Step 15 .
NO -
Is the evaporator temperature sensor OK?
YES -
Go to Step 16 .
NO -
  1. Jump the SCS line with the HDS.
    NOTE: This step must be done to protect the engine control module (ECM)/powertrain control module (PCM) from damage.
  1. Disconnect ECM/PCM connector A (49P).

  1. Check for continuity between the following terminals of ECM/PCM connector A (49P) and the evaporator temperature sensor 2P connector.
    49P:
    2P:
    No. 10
    No. 2
    No. 38
    No. 1

Is there continuity?
YES -
  • KZ, KP, and MA models: Go to Step 19 .
  • Except KZ, KP, and MA models: Go to Step 22 .
NO -
Repair open in the wire(s) between the ECM/PCM and the evaporator temperature sensor.■
Is the temperature control dial OK?
YES -
Go to Step 20 .
NO -

  1. Check for continuity between the following terminals of ECM/PCM connector A (49P) and the heater control panel 6P connector.
    49P:
    6P:
    No. 10
    No. 6
    No. 20
    No. 5
    No. 37
    No. 4

Is there continuity?
YES -
Go to Step 21 .
NO -
Repair open in the wire(s) between the ECM/PCM and the heater control panel. Also check the heater control panel harness.■

  1. Check for continuity between ECM/PCM connector A (49P) No. 37 terminal and body ground.
Is there continuity?
YES -
Repair short to body ground in the wire between the ECM/PCM and the temperature control dial.■
NO -
Go to Step 22 .

  1. Check for continuity between ECM/PCM connector A (49P) No. 38 terminal and body ground.
Is there continuity?
YES -
Repair short to body ground in the wire between the ECM/PCM and the evaporator temperature sensor.■
NO -
Check for loose wires or poor connections at ECM/PCM connector A (49P), the evaporator temperature sensor 2P connector, the A/C pressure switch 2P connector, the A/C switch 5P connector and at the heater fan switch 8P connector. If the connections are good, substitute a known-good ECM/PCM, and recheck. If the symptom/indication goes away, replace the original ECM/PCM.■
  1. Turn the ignition switch to LOCK (0).
  1. Reconnect the A/C pressure switch 2P connector.
  1. Make sure the A/C switch is OFF.
  1. Turn the ignition switch to ON (II).

  1. Measure the voltage between under-dash fuse/relay box connector A (36P) No. 21 terminal and body ground with the under-dash fuse/relay box connectors connected.
Is there battery voltage?
YES -
Repair open in the wire between the A/C pressure switch and the MICU.■
NO -
Check for loose wires or poor connections at the under-dash fuse/relay box. If the connections are OK, substitute a known-good MICU and recheck. If the symptom goes away, replace the original MICU .■