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A/C Refrigerant Monitor

Non-Continuous

Typically completes within 5-10 minutes of driving with the A/C system running on a day above 40°F (4°C).

What This Monitor Checks

The A/C Refrigerant Monitor checks for refrigerant leaks in the air conditioning system by monitoring high-side and low-side refrigerant pressures and correlating them with ambient temperature and compressor operating state. On some vehicles, the PCM tracks refrigerant pressure trends over multiple drive cycles to detect slow leaks. This monitor may also verify compressor clutch engagement and proper cycling behavior to confirm adequate refrigerant charge. This monitor is only present on vehicles where the PCM manages A/C system control (rather than a standalone A/C module).

Why It Matters for Emissions

While A/C refrigerant (R-134a or R-1234yf) does not directly contribute to tailpipe criteria pollutant emissions, both are greenhouse gases with global warming potential. R-134a has a GWP of 1,430 (relative to CO2), and OBD-II regulations require monitoring for refrigerant leaks on applicable vehicles to minimize atmospheric release of these potent greenhouse gases.

Drive Cycle Steps

1

Ensure ambient temperature is above 40°F (4°C) — the PCM disables A/C compressor engagement and monitoring below this threshold.

2

Start the engine, turn the A/C system on to maximum cooling with the blower on medium or high speed.

3

Drive at moderate speeds (30-55 mph) for 5-10 minutes with the A/C running continuously — the PCM needs stable compressor operation to evaluate refrigerant pressures.

4

The PCM monitors high-side and low-side pressure sensor readings against expected values for the current ambient temperature and compressor state.

Prerequisites

  • Ambient temperature must be above 40°F (4°C) — most systems will not engage the compressor below this temperature.
  • The A/C system must be commanded on by the operator — the monitor does not run with the A/C off.
  • High-side and low-side refrigerant pressure sensors must be functional with no active DTCs.
  • Engine must be at normal operating temperature and running at stable RPM (no active misfire or stall conditions).

Common Failure Reasons

  • Slow refrigerant leak from an aging compressor shaft seal, O-ring connection, or condenser stone damage allowing charge to drop below the monitoring threshold.
  • Failed high-side or low-side pressure sensor providing out-of-range readings that prevent the PCM from evaluating system performance.
  • A/C compressor clutch slipping or not engaging fully due to low voltage, worn clutch surfaces, or insufficient clutch air gap.
  • Condenser blockage or fan failure causing abnormally high head pressures that trigger pressure-based fault thresholds.
  • Refrigerant overcharge from improper service causing pressures to exceed expected ranges for the ambient temperature.

Pro Tips

  • This monitor is not present on all vehicles — many older OBD-II vehicles and some manufacturers don't include A/C refrigerant monitoring. Check the scan tool's supported monitors list before troubleshooting.
  • If the monitor won't run in winter, park the vehicle in a heated garage above 40°F to meet the ambient temperature prerequisite, then drive with the A/C on.
  • A/C system pressures should correlate with ambient temperature — at 80°F ambient, expect roughly 25-35 psi low-side and 175-225 psi high-side for R-134a systems at stable idle.
  • When the scan tool shows this monitor as 'not supported,' it simply means the vehicle's PCM does not have A/C refrigerant monitoring capability — this is normal and does not affect emissions test results.

Frequently Asked Questions

What does the A/C Refrigerant Monitor check?

The A/C Refrigerant Monitor checks for refrigerant leaks in the air conditioning system by monitoring high-side and low-side refrigerant pressures and correlating them with ambient temperature and compressor operating state. On some vehicles, the PCM tracks refrigerant pressure trends over multiple drive cycles to detect slow leaks. This monitor may also verify compressor clutch engagement and proper cycling behavior to confirm adequate refrigerant charge. This monitor is only present on vehicles where the PCM manages A/C system control (rather than a standalone A/C module).

How do I get the A/C Refrigerant Monitor to set ready?

Follow the drive cycle: Ensure ambient temperature is above 40°F (4°C) — the PCM disables A/C compressor engagement and monitoring below this threshold. Start the engine, turn the A/C system on to maximum cooling with the blower on medium or high speed. Drive at moderate speeds (30-55 mph) for 5-10 minutes with the A/C running continuously — the PCM needs stable compressor operation to evaluate refrigerant pressures. The PCM monitors high-side and low-side pressure sensor readings against expected values for the current ambient temperature and compressor state. Estimated completion: Typically completes within 5-10 minutes of driving with the A/C system running on a day above 40°F (4°C).

Why does the A/C Refrigerant Monitor keep failing?

Common failure reasons include: Slow refrigerant leak from an aging compressor shaft seal, O-ring connection, or condenser stone damage allowing charge to drop below the monitoring threshold.; Failed high-side or low-side pressure sensor providing out-of-range readings that prevent the PCM from evaluating system performance.; A/C compressor clutch slipping or not engaging fully due to low voltage, worn clutch surfaces, or insufficient clutch air gap..

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Quick Info

Type

Non-Continuous

Completion

Typically completes within 5-10 minutes of driving with the A/C system running on a day above 40°F (4°C).

Resets on Clear

Yes