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Error code reference

Denso Air Conditioner Error Code CF

Loss of cooling detection

Denso codesDenso air conditioner codes

Loss of cooling detection — room temperature minus freeze protection temperature is less than 9°F (5°C) for 1 minute, and this condition occurs 3 times.

First step from the service manual

See troubleshooting chart on page 47. To reset: hold down SET TEMP UP and DOWN buttons simultaneously for 3 seconds.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What CF means on a Denso air conditioner

The CF error code on a Denso air conditioner indicates a loss of cooling detection event. The system monitors the difference between the room temperature sensor reading and the freeze protection temperature sensor reading. When that difference falls below 9°F (5°C) and remains there for 1 continuous minute, the system logs one loss-of-cooling event. If this condition occurs 3 separate times, the CF code is triggered and displayed. This logic is designed to detect situations where the unit is running but failing to produce meaningful cooling, distinguishing true refrigeration failures from brief transient conditions.

The components most likely involved in a CF fault are the refrigerant circuit, the evaporator and its associated sensors, the compressor, and the airflow path through the indoor unit. If refrigerant charge is low or the system has a leak, the temperature differential between room air and the evaporator surface will be insufficient to meet the 9°F threshold. Similarly, a blocked air filter or restricted return air path reduces heat exchange across the coil, which can produce the same narrow temperature gap the control board interprets as a cooling loss.

Additional causes include a faulty indoor temperature sensor or freeze protection sensor that is reporting inaccurate values, a compressor that is not cycling properly, or an expansion valve issue that is limiting refrigerant flow. Because the fault must occur 3 times before the code displays, intermittent conditions can be particularly difficult to diagnose. The diagnostic procedure for this code is detailed in the troubleshooting chart and the reset procedure requires holding the SET TEMP UP and DOWN buttons simultaneously for 3 seconds.

Source: manufacturer service documentation.

Common causes of CF

  1. 01

    Low refrigerant charge or refrigerant leak

    Part replacement

    Insufficient refrigerant reduces the temperature drop across the evaporator coil, preventing the system from achieving the required 9°F difference between room and freeze protection temperatures. Signs include ice buildup on the indoor coil, hissing sounds, or a gradual decline in cooling performance over weeks or months.

  2. 02

    Clogged or heavily restricted air filter

    Wiring / connection

    A dirty filter drastically reduces airflow across the evaporator, limiting heat exchange and allowing room and coil temperatures to converge. Remove and inspect the filter; if it is visibly clogged with dust and debris, clean or replace it before attempting a reset.

  3. 03

    Faulty indoor temperature or freeze protection sensor

    Part replacement

    If either sensor is reading inaccurately, the control board may calculate a false temperature differential that falls below the 9°F threshold even when cooling is normal. Sensors can be tested with a multimeter to verify their resistance values match expected specifications.

  4. 04

    Compressor not operating correctly

    Part replacement

    A compressor that is failing to start, running intermittently, or not reaching proper operating pressure will reduce or eliminate the temperature differential needed to avoid a CF fault. Listen for unusual sounds during operation and check whether the outdoor unit is running when the indoor unit calls for cooling.

  5. 05

    Blocked outdoor unit or condenser airflow restriction

    Wiring / connection

    Debris, vegetation, or physical obstructions around the outdoor unit can cause high head pressure conditions that reduce the system's ability to transfer heat and cool the indoor coil effectively. Inspect the outdoor unit and clear any blockages from the coil face and surrounding area.

See the test procedure for each cause

Frequently asked questions about CF

What does CF mean on a Denso air_conditioner?
The CF code on a Denso air conditioner signals a loss of cooling detection fault. The system measures the difference between the room temperature and the freeze protection temperature, and when that difference stays below 9°F (5°C) for 1 minute, it counts as one loss-of-cooling event. After this occurs 3 times, the CF code is triggered. Common causes include low refrigerant, a dirty filter, or a defective temperature sensor.
How do I reset the CF error code on my Denso air conditioner?
To reset the CF code, press and hold the SET TEMP UP and SET TEMP DOWN buttons at the same time for 3 seconds. However, resetting the code without addressing the underlying cause will typically result in the fault returning. It is recommended to inspect the air filter, check for airflow restrictions, and review the troubleshooting chart before performing the reset.
Will resetting the CF code fix the problem permanently?
Resetting the code clears the fault display but does not repair the underlying condition. Because the CF fault requires the loss-of-cooling event to occur 3 times before displaying, the code will return if the root cause is not corrected. A lasting fix requires diagnosing and resolving the actual problem, such as recharging refrigerant, cleaning the filter, or replacing a faulty sensor.
Is it safe to keep running my Denso air conditioner when the CF code is displayed?
Continuing to operate the unit with an active CF fault is not recommended. The code indicates that the system is not cooling effectively, and running it in this state can put stress on the compressor, which may worsen the fault or cause additional component damage. It is best to address the cause before resuming normal operation.
How much does it cost to repair a Denso air conditioner showing the CF code?
Repair costs vary depending on the root cause. Cleaning or replacing a dirty air filter is inexpensive, typically in the range of a few dollars to around $30. Sensor replacements generally cost between $50 and $150 including labor. If the system requires refrigerant recovery, leak detection, and recharging, costs can range from $150 to $400 or more depending on refrigerant type and labor rates. Compressor replacement represents the most expensive scenario, often ranging from $400 to over $1,000.

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