AC System Diagnosis

Comprehensive diagnostic procedure for the AC system on a 2023 Chevrolet Bolt EUV, including pressure testing, electrical diagnostics, and component verification.

Warnings

Tools required

Parts

• AC system O-rings (if testing fittings) × 1 — Use OEM specification
• AC refrigerant R-134a (if topping off) × 1 — R-134a per system capacity

Preparation

1. Park vehicle on level surface and apply parking brake
2. Ensure vehicle has been off for at least 10 minutes to allow system pressures to equalize
3. Verify customer complaint and note ambient temperature conditions
4. Check cabin air filter condition - replace if restricted as this affects performance
5. Ensure 12V battery is in good condition (low voltage can prevent AC compressor engagement)

Procedure

1. 1

   Perform initial visual inspection
   Inspect all visible AC components under the hood. Check AC condenser (front of vehicle) for damage, debris, or blockage. Inspect all visible AC lines for signs of oil residue indicating leaks. Check electric AC compressor wiring harness for damage or corrosion. Verify cooling fans are not obstructed. Note any obvious damage or oil stains.
2. 2

   Connect scan tool and check for DTCs
   Connect scan tool to OBD-II port. Navigate to HVAC module and check for diagnostic trouble codes. Record all codes present. Check for high voltage system codes that may prevent AC operation. Verify HVAC module communication is normal. Check freeze frame data if codes are present. Common codes include B3935 (AC pressure sensor), U0155 (instrument cluster communication), or P1E00 (high voltage system issues).
3. 3

   Check AC system pressures (static)
   With vehicle off and system at ambient temperature, connect AC manifold gauge set to low and high side service ports. Low side port is on larger diameter line near firewall, high side is on smaller line. Check static pressure - should be approximately 70-90 psi at 70°F ambient (pressure increases with temperature). If pressure is near zero, system has significant leak. If drastically high (over 150 psi static), system may be overcharged or have air contamination.
4. 4

   Test AC compressor activation
   Turn vehicle to ON mode (ready to drive). Set climate control to MAX AC, full cold, highest fan speed. Monitor scan tool data for AC compressor request and activation status. Verify AC compressor clutch relay command (scan tool should show active). Electric compressor should activate - listen for operation sound and feel vibration at compressor housing. If no activation, check fuse F59 (HVAC compressor) in underhood fuse block. Measure voltage at compressor connector - should see battery voltage when commanded on.
5. 5

   Check running pressures and temperatures
   With AC running at MAX and vehicle in READY mode, monitor gauge pressures. Target values at 70-80°F ambient: Low side 25-40 psi, High side 150-250 psi (varies with ambient temp). Use infrared thermometer to check vent temperatures - should achieve 38-45°F. Monitor both cooling fans - they should activate when AC is on. Check temperature of AC lines: suction line (low side) should be cold to touch, liquid line (high side) should be warm. Document all readings.
6. 6

   Test AC pressure sensor
   Locate AC pressure sensor on high side AC line near compressor. With ignition on and AC off, use scan tool to monitor AC pressure sensor reading - should match static pressure from gauges. Check sensor connector for corrosion. With engine running, sensor reading should vary with compressor cycling. If reading is implausible or frozen, test sensor: disconnect electrical connector, measure resistance across sensor terminals (should be 4500-5500 ohms at room temp). Check for 5V reference voltage at connector harness side.
7. 7

   Inspect evaporator temperature sensor
   Access evaporator temperature sensor behind glove box (may require glove box removal for better access). This sensor prevents evaporator icing. Check scan tool reading - should show temperature near ambient initially, then drop to 32-40°F during operation. If reading is implausible, test sensor resistance. Sensor prevents compressor operation if evaporator approaches freezing. Verify sensor connector is secure and free of corrosion.
8. 8

   Check cooling fan operation
   The Bolt EUV has two electric cooling fans critical for AC operation. With AC on MAX, both fans should run. Use scan tool to command fans on individually - left fan and right fan. Each should respond to command. Check fan fuses in underhood fuse block. Listen for abnormal bearing noise. Verify fan shroud is intact and fans are not obstructed. Poor fan operation causes high side pressure to exceed limits and compressor shutdown.
9. 9

   Perform leak detection (if low pressure found)
   If system pressure is low, perform leak detection. Use electronic leak detector or UV dye method. Check all line fittings, compressor shaft seal, condenser, and evaporator drain tube for UV dye traces. Common leak points: compressor fittings, condenser stone damage, evaporator (oil residue at drain). If using electronic sniffer, probe all connections, particularly at service ports and line connections. Mark any leak locations for repair.
10. 10

    Test blend door and actuator operation
    If pressures and temperatures are correct but airflow is warm, check blend door operation. Use scan tool to command temperature actuator through full range (cold to hot). Listen for actuator motor movement behind dash. Check for binding or failure to complete range. Monitor actuator position sensor feedback - should track commanded position. Place hand at vents and feel for temperature change as actuator moves. Binding blend door or failed actuator causes warm air complaints despite functioning AC.
11. 11

    Document findings and determine root cause
    Review all diagnostic data collected: DTCs, pressure readings, temperature measurements, component tests. Compare findings to specifications. Determine root cause: low refrigerant/leak, compressor failure, electrical issue, sensor fault, blend door problem, or blocked airflow. Document specific failed component(s) and supporting data. If system needs refrigerant recovery and recharge, note amount recovered vs. specification (system capacity is approximately 1.2 lbs R-134a). Prepare detailed diagnostic report with next repair steps.

Reassembly

1. Disconnect AC manifold gauges carefully, minimizing refrigerant loss
2. Replace service port caps on both high and low side ports
3. Reinstall any panels or components removed for access
4. Clear any soft codes from diagnostic scan if repairs will be performed
5. If system was found low on refrigerant, advise customer that leak repair and recharge are needed

Verification

• Verify all diagnostic findings are documented with specific pressure and temperature readings
• Confirm root cause has been identified with supporting data
• Ensure customer is informed of findings and recommended repairs
• If system is functional, verify vent temperatures are 38-45°F at MAX AC setting
• Confirm no refrigerant was lost during diagnostic procedure
• Verify all tools and equipment have been removed from vehicle

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