Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
A/C Pressure Switch Circuit Troubleshooting
- Do not use this troubleshooting procedure if any of the following items are operative; A/C condenser fan, radiator fan, A/C compressor, or if the heater is inoperative. Refer to the symptom troubleshooting index.
- Before performing symptom troubleshooting, check for powertrain DTCs: '00-05 models (see GENERAL TROUBLESHOOTING INFORMATION ); '06-09 models (see GENERAL TROUBLESHOOTING INFORMATION ).
- Disconnect the A/C pressure switch 2P connector.
- Turn the ignition switch to ON (II).
- Measure the voltage between A/C pressure switch 2P connector terminal No. 2 and body ground.
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Is there about 5 V?
YES -Go to step 4.
NO -Go to step 15.
- Turn the ignition switch to LOCK (0).
- Check for continuity between A/C pressure switch terminals No. 1 and No. 2.
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Is there continuity?
YES -Go to step 6.
NO -Go to step 17.
- Reconnect the A/C pressure switch 2P connector.
- Disconnect the HVAC control unit 30P connector.
- Turn the ignition switch to ON (II).
- Measure the voltage between HVAC control unit 30P connector terminal No. 12 and body ground.
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Is there about 5 V?
YES -Go to step 10.
NO -Repair open in the wire between the HVAC control unit and the A/C pressure switch.
- Turn the ignition switch to LOCK (0).
- Measure the resistance between HVAC control unit 30P connector terminals No. 7 and No. 10.
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Is the resistance less than 24 k Ω?
YES -Go to step 12.
NO -Repair cause of high resistance in the evaporator temperature circuit.
- Reconnect the HVAC control unit 30P connector.
- Turn the ignition switch to ON (II).
- Check the blower motor operation at several speeds.
Does the blower motor operate at all speeds?
YES -Check for loose wires or poor connections at the HVAC control unit 30P connector, and at the A/C pressure switch 2P connector. If the connections are good, substitute a known-good HVAC control unit, and recheck. If the symptom/indication goes away, replace the original HVAC control unit.
NO -Repair the problem in the blower motor circuit.
- Make sure the A/C switch is OFF.
- Using a backprobe set, measure the voltage between ECM connector A (32P) terminal No. 27 and body ground with the ECM connectors connected ('00-05 models) or between ECM connector E (31P) terminal No. 28 and body ground with the ECM connectors connected ('06-09 models).
'00-05 models
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'06-09 models
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Is there about 5 V?
YES -Repair open in the wire between the ECM and the A/C pressure switch.
NO -Check for loose wires or poor connections at ECM connector A (32P) ('00-05 models), or ECM connector E (31P) ('06-09 models). If the connections are good, substitute a known-good ECM, and recheck. If the symptom/indication goes away, replace the original ECM: '00-05 models (see ECM REPLACEMENT ); '06-09 models (see ECM REPLACEMENT ).
- Check for proper A/C system pressure.
Is the pressure within specifications?
YES -Replace the A/C pressure switch (see A/C LINE REPLACEMENT ).
NO -Repair the A/C pressure problem.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.