What are the Symptoms of a Bad or Failing Ambient Temperature Sensor?

Diagnosing a bad or failing Ambient Temperature Sensor.

  1. The air conditioning  “AUTO MODE “ won’t  work
  2. Inconsistent cooling or not cooling at all.
  3. A/C compressor inoperative
  4. Incorrect reading on temperature gauge. Usually a default negative temperature.

Thermistor.

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. That’s 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 compressor’s clutch is energized while the oil is cold and thick, improper compressor-lubrication would result.

Where the ambient temperature sensor is usually mounted?

Location:

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 won’t flow and lubricate the system properly.

The ambient temperature sensor prevents the compressor from running when it’s too cold for the system to work safely. These switches open when the temperature drops below a preset temperature,usually below 32° F

Why did my car AC stop blowing air ?

My car A/C stop blowing air from the vents.

Common reasons for this to happen:

  • A/C blower motor circuit blown fuse
  • Bad blower motor resistor
  • Blower motor shorted
  • Bad blower motor control switch
  • Poor ground connection
  • Poor blower motor connections

Ram air flowing through the evaporator does not provide enough air flow inside the vehicle for cooling purposes. So, a blower is used to force the air along. An electric motor spins a fan, forcing the air into ducts, which direct it to the particular vent selected by the operator.

If the blower motor gets full voltage, it will run at high speed, but that is not always desirable. Therefore resistors are used to cut the speed down. The fan switch directs the current flow through one or more resistors to achieve the slow and medium speeds.