Diagnosing a bad or failing Ambient Temperature Sensor.
- The air conditioning† ďAUTO MODE ď wonít †work
- Inconsistent cooling or not cooling at all.
- A/C compressor inoperative
- Incorrect reading on temperature gauge. Usually a default negative temperature.
The most common variable resistor is a thermistor.Thermistors change resistance based on temperature changes. There are two different styles of thermistor: NTC (Negative Temperature Coefficient) and PTC (Positive Temperature Coefficient).The difference is in how they react to temperature changes.
As temperature rise:
-PTC thermistor-resistance increases
-NTC Thermistor-resistance decreases
The NTC thermistor is more common than the PTC thermistor.
Here are some examples of thermistor in automotive circuits:
- Engine temperature sensor
- Evaporator temperature sensor
- Ambient temperature sensors-In-car and outside sensors
- A/C High Side Refrigerant Temperature Sensors
- A/C Low Side Refrigerant Temperature Sensors
- Sun Load Sensors (Not all sun load sensors are thermistor some are photoresistors.A photoresistor measures the amount of light hitting it .As the light intensity increases , sensor resistance decreases. Thatís the why a photo resistor works so well as a sun load sensor. Some manufacturers use a photodiode. A photodiode works in a manner similar to the photoresistor.
What does the ambient temperature sensor do?
It prevents the compressor from engaging when ambient temperatures get too low. The oil that resides inside of a compressor can get very cold during the winter months. If the compressorís clutch is energized while the oil is cold and thick, improper compressor-lubrication would result.
Where the ambient temperature sensor is usually mounted?
Mounted to the radiator support, in front of the condenser where it can sense outside temperatures without being affected by engine heat.
How does ambient temp sensor work?
A lot of air conditioning systems are supposed to run when you turn the defroster on, to help remove moisture from the air. But when outside temperatures are very low refrigerant oils wonít flow and lubricate the system properly.
The ambient temperature sensor prevents the compressor from running when itís too cold for the system to work safely. These switches open when the temperature drops below a preset temperature,usually below 32į F