Service Overview
- Average Cost: KES 2,000 – 6,000 depending on sensor type
- Replacement Time: 45 minutes to 2 hours
- Common Sensor Types: Temperature sensors, pressure sensors, humidity sensors
- Impact: Directly affects cooling accuracy and system efficiency
- Diagnostic Fee: Often included in service call charge
Air conditioner sensors act as the system’s sensory organs, constantly monitoring conditions and sending data to the control board for processing. When these critical components fail or provide inaccurate readings, your AC can’t maintain comfortable temperatures, may run inefficiently, or could damage itself through improper operation. Understanding sensor function and replacement helps you maintain optimal cooling performance.
Types of AC Sensors and Their Functions
Modern air conditioners employ multiple sensor types working together to deliver precise climate control. Temperature sensors, the most common type, monitor air temperature at various locations including the room, the evaporator coil, and sometimes the outdoor ambient air. These sensors tell the control board when target temperatures are reached and when cooling cycles should begin or end.
Pressure sensors mounted on refrigerant lines monitor system pressures, protecting the compressor from dangerous operating conditions. High-pressure sensors prevent operation when pressures exceed safe limits, while low-pressure sensors detect refrigerant leaks or other issues causing insufficient pressure. Thermistor sensors use resistance changes to measure temperature with high accuracy, providing the precise data needed for efficient operation. Some advanced systems include humidity sensors that adjust operation based on moisture levels, optimizing both temperature and comfort.
Symptoms of Sensor Failure
Faulty sensors create various operational problems depending on which sensor fails and how it fails. If your AC runs constantly without reaching the set temperature, the temperature sensor may be reading incorrectly, telling the control board that the room remains too warm. Conversely, short cycling where the unit turns on and off every few minutes often indicates a sensor providing false “satisfied” readings to the control board.
Error codes displayed on your AC’s panel frequently point to specific sensor failures, with each code corresponding to particular sensors or circuits. The air conditioner might cool unevenly, maintaining comfortable temperatures only in certain areas while leaving others too warm. Some sensor failures trigger safety shutoffs, causing the unit to cease operation entirely to prevent damage. Unusual frost buildup on indoor coils can result from malfunctioning evaporator temperature sensors that fail to properly regulate the refrigeration cycle.
Diagnostic Testing
Professional diagnosis begins with retrieving any error codes stored in the AC’s control system, which often identify which sensor is malfunctioning. Technicians then use multimeters to test sensor resistance at known temperatures, comparing readings against manufacturer specifications. For temperature sensors, this involves measuring resistance while the sensor is at room temperature, then comparing it to expected values for that temperature.
Pressure sensors require different testing methods, often involving comparing sensor readings to actual pressures measured with mechanical gauges attached to service ports. If sensor readings and mechanical measurements differ significantly, the sensor needs replacement. Some advanced diagnostics involve forcing the AC through various operating modes while monitoring sensor outputs in real-time to identify intermittent failures that might not appear during static testing.
The Replacement Procedure
Sensor replacement procedures vary based on sensor type and location. Temperature sensors often mount near the evaporator coil, requiring removal of access panels to reach them. Technicians must first power down the unit completely before handling sensors connected to control boards. The old sensor is disconnected from its wiring harness, and its exact position is noted since sensor placement affects reading accuracy.
For evaporator sensors, positioning within the coil fins is critical. Too close to the coil surface results in readings that don’t reflect actual air temperature; too far away causes delayed response to temperature changes. Technicians secure the new sensor in the optimal position, ensuring it maintains good thermal contact with the air stream while avoiding direct contact with cold metal that would skew readings.
Pressure sensor replacement involves safely recovering refrigerant before breaking into the sealed system. This process requires proper equipment and licensing since refrigerant release into the atmosphere is illegal. Once the system is depressurized, the old sensor is removed, threads are inspected and cleaned, and the new sensor is installed with proper torque to prevent leaks. After sensor installation, the system is evacuated, recharged with the correct refrigerant amount, and leak-tested.
Calibration and System Integration
Unlike simple mechanical parts, sensors often require calibration after installation to ensure accurate readings. Some modern control boards automatically calibrate new sensors during initial power-up by comparing readings across multiple sensors and adjusting offsets as needed. Other systems require manual calibration where technicians input known temperature or pressure values and adjust the control board’s interpretation of sensor signals.
After calibration, the system undergoes operational testing across its full range. Technicians cycle the unit through various modes, monitoring sensor readings and comparing them to actual measured conditions. They verify that temperature sensors trigger appropriate system responses, that pressure sensors activate safety cutoffs at proper thresholds, and that all sensors communicate correctly with the control board without generating false error codes.
Preventive Considerations
While sensors eventually wear out, several factors accelerate their deterioration. Moisture infiltration into electrical connections causes corrosion that affects sensor accuracy before causing complete failure. Regular maintenance that keeps drainage systems clear prevents moisture problems. Vibration from poorly mounted components or failing motors can damage sensor connections over time. Ensuring proper mounting and addressing mechanical issues promptly protects sensor integrity.
Voltage irregularities can damage electronic sensors, making surge protection a worthwhile investment. Some sensors fail gradually rather than suddenly, slowly drifting out of calibration over years. This is why annual maintenance inspections should include sensor testing even when no obvious problems exist, catching degradation before it significantly impacts performance or causes secondary damage to other components.
