Why Does My Check Engine Light Comes On When Air Conditioner Is On? 5 Hidden Causes And Quick DIY Fixes Covered Here!

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check engine light comes on when air conditioner is on

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You turn on your car’s air conditioner, and the check engine light comes on along with the AC. This indicates a problem with the air conditioner.

So, why does the check engine light come on when the air conditioner is on? The check engine light comes on when the A/C is on due to the following reasons.

  • Faulty A/C compressor
  • Damaged thermostat
  • Loose electrical connections
  • Blown A/C fuse
  • Low refrigerant levels

For this article, I shall dig deep into the leading causes of the check engine light coming on when the air conditioner is on and the possible solutions.

check engine light comes on when air conditioner is on

Check Engine Light Comes On When Air Conditioner Is On – (Summary Of Causes And Fixes!)

Let’s get an overview of the leading causes for the check engine light being on when the A/C is on and how to fix them.

Causes Of Check Engine Coming On When A/C Is OnPossible Fix
Faulty A/C compressorReplace the compressor if it is badly damaged.
Faulty thermostatReplace it if it is completely damaged.
Loose electrical connections1. Check the wiring and repair broken and loose connections.

2. Replace the completely damaged cables.
Blown fuseLocate the damaged fuse and replace it with its OEM part.
Low refrigerant levels1. Check for any leaks and seal them completely.

2. Refill the refrigerant.

Check Engine Light Comes On When Air Conditioner Is On – Causes and Fixes in Detail

Let’s discuss why the check engine light comes on when the air conditioner is on. Follow the steps carefully when solving specific problems with your vehicle.

1. Faulty Air Conditioner Compressor

The air compressor in the A/C increases the pressure and temperature of the refrigerant to facilitate smooth flow in the heat exchange. It creates a pressure difference within the system, ensuring a constant coolant flow.

When you turn on the A/C with a faulty compressor, the A/C malfunctions, causing the engine to overheat, and the check engine light comes on.

Solution

  • Start by diagnosing the problem with your vehicle using an OBDII scanner and reading the codes against a manual guide.
  • Inspect for any blockage or contaminants and clean it by emptying the refrigerant as you refill from the top.
  • For the damaged compressor cycling unit, repair or replace it using its exact OEM parts.

2. Broken Or Damaged Thermostat

When the engine temperature is low, the thermostat closes and locks the refrigerant to ensure it only circulates in the engine block.

When the temperature in the engine block is high, it opens and allows the coolant to circulate through the radiator for efficient cooling.

A faulty thermostat fails to open when the temperature rises in the engine block, causing the check engine light to come on.

Solution

Open the hood and locate the thermostat next to the engine block. Check the spring in the thermostat to ensure it opens and closes appropriately when pressure is applied.

For a faulty thermostat, replace it with its OEM new thermostat cap parts.

3. Loose Electrical Connections

The battery powers the A/C, and a loose connection causes a low or no power supply. When the A/C is turned on, it fails to cool the interior, causing the temperature inside to rise.

With a loose connection, the engine temp spikes and then returns normal as the wires keep connecting and disconnecting. High temperatures around the engine cause the check engine light to come on when the A/C is on.

Solution

Inspect the wiring connections, repair any naked wires, and tighten any loose connections. Replace the completely damaged wires with new cables.

4. Low Refrigerant Levels

The A/C operates based on sufficient refrigerant in the compressor to facilitate the creation of enough pressure difference. When the refrigerant is below the standard level, it causes the compressor to stop functioning.

Temperature rises in the engine, causing the check engine light to be illuminated. There may also be no check engine light, but car runs rough, indicating possible low refrigerant levels.

Solution

Check for any leakages and seal them completely. If the system has lots of leaking points, consider replacing the entire unit with a new system.

Inspect the refrigerant level in the reservoir and top it up accordingly with the appropriate refrigerant type, such as the Interdynamics EZ Chill Refrigerant.

5. Blown A/C Fuse

When the air conditioner fuse is blown, the A/C doesn’t receive power for efficient cooling, causing the interior to heat up. The engine temperature rises, causing the check engine light to come on.

Solution

Check for the blown-out fuse for the A/C line and replace it by following the process below.

  • Open the fuse box cover by unclipping the hooks holding the plastic cover on top to expose the fuses.
  • Locate the A/C fuse using a testing screw, remove it, and replace it with a new fuse.

How To Diagnose Your Vehicle Using The OBDII Scanner

Most of the time, I would advise you to diagnose the problem with the A/C using an OBDII scanner before repairing or replacing any part.

Follow the steps below to diagnose the problem causing the check engine light to illuminate when the A/C is on.

Step 1

Locate the link for data collection found on the driver’s side.

Step 2

Connect the OBDII scanner to the data link collector.

Step 3

Turn the ignition to the ‘on’ position.

Step 4

Scroll the scanner screen to diagnose the A/C.

Step 5

Input the vehicle’s specifications, such as the model and year of make.

Step 6

Scan the vehicle and read the codes on the screen.

Step 7

Use a manual or online code table to get the meaning of the displayed codes.

You can get the help of a professional to scan the vehicle’s A/C system and rectify each specific problem, as discussed above.

How To Reset The Check Engine Light?

To reset the check engine light after addressing the underlying issues, follow the steps below.

  • Disconnect the battery’s terminals to reset the electrical system.
  • Attach the negative terminal to any metallic part to drain any charges completely.
  • Wait for up to 15 to 20 minutes before reconnecting the battery.
  • Turn on all electrical appliances in your vehicle before starting the engine.
  • Then, drive your vehicle for about five minutes at a speed of 30 mph.
  • Stop the vehicle and turn off the engine. The check engine light will be off.

How Much Would It Cost To Replace The A/C System In My Vehicle?

The replacement cost of the air conditioner system varies depending on the make and model of your car. However, on average, replacing the A/C will cost between $500 and $2500, depending on the type of A/C you install.

Conclusion

The check engine light indicates problems with the engine computer system, fuel and emission systems, and the cooling system. However, if the check engine light only comes on when the A/C is on, the problem is with the air conditioner and its components.

Have the vehicle ECU diagnosed and the exact problem addressed before it causes further damage to the engine. You may require professional assistance if you are unfamiliar with A/C repairs.

Resources

https://www.researchgate.net/publication/336861522_OBD-II_sensor_diagnostics_for_monitoring_vehicle_operation_and_consumption
https://www.researchgate.net/publication/255220886_Thermostat_Interface_and_Usability_A_Survey
https://www.researchgate.net/publication/366715571_Study_of_a_Compressor_Refrigeration_Circuit

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