Car Ac Stopped Working Then Started Again

Experiencing intermittent air conditioning in your car is frustrating, especially during hot weather. One minute you're enjoying cool air, and the next you're sweating. This inconsistent performance can stem from various causes, ranging from minor issues to more complex problems. Let's explore some common reasons why your car's AC might stop working and then start again, and what you can do to diagnose and potentially resolve the issue.

Common Causes of Intermittent AC Failure

Several factors can contribute to a car AC system cycling on and off. Here's a breakdown of the most frequent culprits:

1. Low Refrigerant Level

This is often the first thing to suspect. Your AC system relies on refrigerant (like R-134a or R-1234yf) to cool the air. If the refrigerant level is low, the compressor may not engage consistently, leading to intermittent cooling. A leak is typically the underlying cause of low refrigerant. These leaks can occur at various points in the system, including:

Hoses and Connections: Over time, rubber hoses can dry out and crack, and connections can loosen, creating leak paths.
Condenser and Evaporator: These components are susceptible to damage from road debris or corrosion, which can lead to leaks.
Compressor Seals: The compressor shaft seal is a common leak point, especially as the compressor ages.

Diagnosis: While a professional AC system diagnosis is recommended, you can visually inspect hoses and connections for obvious signs of damage or oily residue. You can also purchase a refrigerant gauge and attempt to check the system pressure, but this requires caution and proper knowledge. Be very careful when dealing with refrigerants, as they can cause frostbite.

Solution: If the refrigerant is low, adding more without addressing the leak is only a temporary fix. The system will eventually leak again. The best approach is to have a professional locate and repair the leak, then recharge the system with the correct amount of refrigerant. Cost can range from $150 for a simple hose replacement and recharge to $800+ for a more complex repair like replacing the condenser.

2. Faulty Compressor Clutch

The compressor clutch engages and disengages the compressor, allowing it to pump refrigerant. If the clutch is failing, it may not engage consistently, leading to intermittent AC operation. The clutch relies on an electrical signal to engage, and a failing clutch might receive a weak or intermittent signal.

Diagnosis: Listen for a clicking sound when the AC is turned on. This is the sound of the clutch engaging. If you don't hear the click, the clutch may not be engaging. You can also visually inspect the clutch while someone turns the AC on and off. Look for the clutch plate spinning when the AC is on and stopping when it's off.

Solution: Replacing the compressor clutch is often more cost-effective than replacing the entire compressor, especially if the compressor itself is still functioning properly. However, the labor involved can still be significant. Expect to pay between $300 and $700 for this repair.

3. Electrical Issues

Electrical problems, such as loose connections, corroded wiring, or a faulty relay, can disrupt the power supply to the AC system components, including the compressor and cooling fan. An intermittent signal from the car's computer can also trigger this.

Diagnosis: Check the fuses related to the AC system. A blown fuse can cause the AC to stop working. Use a multimeter to test the continuity of the fuses. Look for any damaged or corroded wiring connections, especially around the compressor, condenser fan, and relays. A faulty relay can also cause intermittent AC operation. You can try swapping the AC relay with another relay of the same type to see if that resolves the issue.

Solution: Replacing a fuse is a simple and inexpensive fix. Repairing or replacing damaged wiring can be more complex and may require professional help. Replacing a faulty relay is also relatively inexpensive. If the problem stems from a faulty computer sending intermittent signals, a mechanic will have to diagnose the root cause of the computer malfunction.

4. Clogged Cabin Air Filter

While a clogged cabin air filter won't directly cause the AC to stop working entirely and then start again, it can significantly reduce airflow through the system. This can make the AC appear to be working intermittently, as the airflow is restricted and the cooling is less effective, especially at lower speeds. If the airflow is poor, the evaporator core may freeze up, further reducing cooling until it thaws.

Diagnosis: Check the cabin air filter. It's usually located behind the glove compartment or under the dashboard. A dirty or clogged filter will be visibly dirty and may restrict airflow.

Solution: Replacing the cabin air filter is a simple and inexpensive DIY task. Cabin air filters are available at most auto parts stores and typically cost between $10 and $30. Replacing the filter can significantly improve airflow and AC performance.

5. Faulty Pressure Sensors

The AC system uses pressure sensors to monitor the refrigerant pressure. If a pressure sensor is faulty, it may send incorrect readings to the car's computer, which can then shut off the compressor to prevent damage. These sensors are designed to protect the system, but can also cause problems when they themselves are faulty.

Diagnosis: Pressure sensor issues are best diagnosed by a professional using a scan tool to read the sensor data and identify any abnormalities. Often, a fault code related to the pressure sensor will be stored in the computer's memory.

Solution: Replacing a faulty pressure sensor requires specialized tools and knowledge, including the ability to properly evacuate and recharge the AC system. Expect to pay between $150 and $400 for this repair.

6. Overheating Engine

In some vehicles, the AC compressor is automatically disengaged when the engine temperature gets too high. This is a safety feature to prevent further strain on the engine. If your engine is overheating intermittently, the AC may cut out and then resume working once the engine temperature drops.

Diagnosis: Monitor your engine temperature gauge. If it's frequently running hotter than normal, you may have an overheating issue. Check your coolant level and look for any signs of coolant leaks.

Solution: Addressing an overheating issue requires diagnosing the underlying cause, which could be a faulty thermostat, a clogged radiator, a leaking coolant hose, or a failing water pump. These repairs can range from a few hundred dollars to over a thousand dollars, depending on the severity of the problem.

Troubleshooting Steps

Here are some steps you can take to troubleshoot intermittent AC failure:

Check the basics: Ensure the AC is turned on, the blower fan is working, and the cabin air filter is clean.
Listen for the compressor clutch: Listen for a clicking sound when the AC is turned on. If you don't hear it, the clutch may not be engaging.
Inspect for leaks: Visually inspect hoses and connections for any signs of leaks or oily residue.
Check the fuses and relays: Ensure the fuses related to the AC system are intact and the relays are functioning properly.
Monitor engine temperature: Watch the engine temperature gauge for any signs of overheating.

When to Seek Professional Help

If you've tried the basic troubleshooting steps and the AC is still working intermittently, it's best to seek professional help from a qualified mechanic. Diagnosing AC problems requires specialized tools and knowledge, including the ability to safely handle refrigerants and interpret diagnostic data. A professional can accurately diagnose the problem and recommend the appropriate repair.

Estimated Costs: Keep in mind the repair costs mentioned above are just estimates and can vary depending on the make and model of your car, the location of the repair, and the mechanic's labor rates. Always get a written estimate before authorizing any repairs.

By understanding the common causes of intermittent AC failure and taking the appropriate troubleshooting steps, you can hopefully get your car's AC working reliably again and enjoy a comfortable ride, even on the hottest days. Good luck!