How to Check Your AC Compressor: A Comprehensive Guide

Your air conditioning (AC) system is a vital part of your home, especially during the sweltering summer months. At the heart of this system lies the AC compressor, the workhorse responsible for circulating refrigerant and cooling your home. When the compressor malfunctions, you’ll likely notice a significant decrease in cooling power, or perhaps no cooling at all. Diagnosing a faulty compressor can save you money and time by pinpointing the issue before it escalates. This comprehensive guide will walk you through the steps to check your AC compressor, enabling you to determine if it’s the source of your cooling problems.

Understanding the AC Compressor’s Role

Before we dive into the troubleshooting process, it’s important to grasp the fundamental role of the AC compressor. Think of it as the pump within your air conditioning system. It takes low-pressure, gaseous refrigerant and compresses it into a high-pressure, hot gas. This hot gas then travels through the condenser coils, where it releases heat to the outside air and condenses into a high-pressure liquid. This high-pressure liquid refrigerant then flows to the expansion valve, where the pressure is reduced and then the refrigerant passes into the evaporator coils to absorb heat from inside the house before heading back to the compressor. If the compressor isn’t functioning correctly, this cycle is disrupted, and your AC unit will fail to cool your home.

Common Signs of a Failing AC Compressor

Before you start your inspection, be on the lookout for these common symptoms of a failing AC compressor:

• Lack of Cooling: This is the most obvious sign. If your AC is running but not producing cold air, a faulty compressor is a strong suspect.
• Unusual Noises: Grinding, rattling, clicking, or screeching sounds emanating from the outdoor unit (where the compressor is located) can indicate internal damage or wear.
• Hard Starting: If your compressor struggles to start, making a loud humming sound or failing to turn on, it may indicate motor problems.
• Circuit Breaker Tripping: A compressor that’s drawing too much power due to a malfunction can trip your circuit breaker repeatedly.
• Visible Damage: Examine the compressor unit for signs of physical damage, such as leaks, dents, or corrosion.
• Warm Air: Blowing warm air instead of cool air consistently even after the AC has been running for a while,
• Refrigerant Leaks: In some cases, a compressor leak can cause a refrigerant leak that leads to inadequate cooling and ice build-up.

Safety Precautions

Working with electrical components can be dangerous. Before you start any troubleshooting, follow these vital safety precautions:

• Turn Off the Power: Completely shut off the power to your AC unit at the breaker panel. This will prevent electrical shocks.
• Never Work Alone: Have someone nearby in case of an emergency.
• Wear Protective Gear: Safety glasses and gloves can protect you from potential hazards.
• If Unsure, Call a Professional: If you are uncomfortable with any of the steps or unsure about what you are doing, it’s always best to call a licensed HVAC technician.

Tools You’ll Need

To perform the checks, you’ll require a few basic tools:

• Multimeter: For testing electrical continuity and voltage.
• Screwdrivers: Phillips and flathead screwdrivers for removing the access panels.
• Wrench Set: For loosening or tightening connections if necessary.
• Flashlight: For seeing clearly inside the unit.
• Wire Brush or Soft Cloth: To clean up any corrosion or debris.

Step-by-Step Guide to Checking Your AC Compressor

Now, let’s move on to the practical steps for checking your AC compressor. Remember to proceed cautiously and methodically.

Step 1: Visual Inspection

Begin with a careful visual inspection of the entire outdoor unit, paying particular attention to the compressor housing:

1. Examine for Physical Damage: Look for dents, cracks, corrosion, or any other visible damage. Note any leaks or signs of oil residue, as this might indicate a refrigerant leak.
2. Check the Wiring: Examine the wiring around the compressor for loose connections, frayed wires, or burnt insulation.
3. Inspect the Access Panel: Make sure the compressor access panel is securely attached. Remove it (after turning off the power, of course) to get a better look at the internal components.
4. Inspect the Run Capacitor: Check the run capacitor (a cylindrical component, usually black or gray) for signs of bulging, cracking, or leaks. If you find any of these issues, the capacitor could be the culprit, which is a more common cause of compressor failure.

Step 2: Check the Compressor’s Electrical Connections

After the visual inspection, check the electrical connections with a multimeter (ensure power is still off at the breaker):

1. Locate the Terminals: Find the terminals on the compressor. These are usually marked with letters like C (Common), R (Run), and S (Start).
2. Test for Continuity: Use your multimeter, set to the continuity setting, to check for continuity between each of these terminals and to the compressor’s body. There should be no continuity between any of the terminals to the compressor body. If there is, it could indicate a shorted compressor and must be addressed by a professional. There should also be continuity between the individual terminals as follows, which indicate good compressor windings. However, the exact readings will vary based on the compressor type so the best thing to do is to compare the readings you get with the manufacturer’s recommended resistance readings which are usually listed on the compressor itself. A significant deviation from those readings indicates a problem with the compressor windings:
• Continuity between terminals C and R.
• Continuity between terminals C and S.
• Continuity between terminals R and S.
3. Check for Ground Fault: Test for continuity between any of the terminals and a metal part of the compressor casing. If there’s continuity, it indicates a ground fault which would require the compressor to be replaced by a professional.

Step 3: Check the Run Capacitor

As mentioned earlier, a faulty run capacitor is a common cause of compressor problems. Here’s how to check it:

1. Visually Inspect Again: Check for any physical damage, swelling, or leaks.
2. Test with Multimeter (Capacitor setting): Set your multimeter to the capacitance setting (usually marked with “F” or “uF”). Carefully disconnect the capacitor from its terminals, noting which wire goes to which terminal. Touch the multimeter probes to the capacitor terminals, if you’re unsure about the capacitor’s proper functionality, compare the reading to its original rating, which is usually printed on the capacitor itself. A value that is substantially lower (more than about 10% low) than its rated value means that the capacitor is likely to be the problem. Replace it accordingly.
3. Capacitor Discharge: Before attempting a capacitor check, ensure that you discharge the capacitor so that you don’t get a shock. To discharge, take a screwdriver with an insulated handle and touch both the leads of the capacitor. Be very careful when doing this.

Step 4: Listening for Unusual Noises (After Re-establishing Power)

If the visual checks and electrical checks haven’t pointed towards an obvious fault and all the values have been within the manufacturer’s recommended ranges, you might need to listen to the compressor while it’s running. Remember to re-establish power at the breaker panel (you will need to do this after disconnecting the capacitor). If the compressor still struggles to start or if you still hear any of the unusual noises mentioned above, you may have an issue with the compressor.

1. Power On and Listen: With caution, turn the power back on at the breaker panel and listen to the compressor as it starts up. Pay attention to the sounds:
• Humming: Indicates the compressor might be trying to start but is encountering resistance.
• Clicking: Can signal a relay issue or a potential compressor lock-up.
• Grinding/Rattling: Indicates a mechanical problem and requires a professional inspection and possibly repair.
• Screeching: Could mean there is excessive internal friction and wear inside the compressor.

Note: If the breaker trips again soon after restarting, there is a significant problem.

Step 5: Check the Compressor’s Amperage Draw

A clamp-on amp meter is required to check the compressor’s amperage draw:

1. Locate the Compressor Wires: Find the wires leading to the compressor.
2. Clamp on Amp Meter: Place the clamp-on amp meter around ONE of the wires leading to the compressor.
3. Compare Reading to Nameplate Rating: Turn the AC on and monitor the reading on the amp meter. Compare this reading with the RLA (Rated Load Amperage) specified on the compressor’s nameplate. An amperage draw that is significantly higher than the RLA indicates a problem with the compressor.

Interpreting Your Findings

After performing these checks, you’ll have a better idea of the compressor’s condition:

• If the Capacitor is faulty: A bad capacitor could be the cause for the compressor not working properly. In this instance, replacing the capacitor can solve the issue.
• If you detect a ground fault: If there’s continuity between the terminals and the compressor casing, there is an electrical short and your compressor needs replacing by a professional.
• If the Compressor is seized: If the compressor is not running when power is supplied to the unit, after taking all precautions, the compressor could be seized up and will have to be replaced.
• If the Readings are abnormal: If your readings are well outside the range specified by the compressor’s manufacturer, there may be issues with the windings inside the compressor that may require a replacement of the unit.
• If everything seems ok: If the visual inspections and electrical checks appear to be normal, it could be a refrigerant issue and could be an indication of a leak, meaning the system will require a recharge, or, in rare cases, it could be an issue with other components in the system such as a clogged air filter.

When to Call a Professional

While this guide provides a good starting point, some issues are best left to the professionals. Call an HVAC technician if:

• You are uncomfortable performing any of the tests.
• You suspect a refrigerant leak.
• You find electrical shorts or ground faults.
• The compressor needs to be replaced.
• You are unable to diagnose the exact problem.
• You are still having cooling problems after performing these checks.

Preventative Maintenance

Regular maintenance can help extend the life of your AC compressor. Here are a few tips:

• Clean the Outdoor Unit: Regularly clear any debris (leaves, grass, branches) from around the outdoor unit.
• Change Air Filters: Change your air filters regularly to ensure proper airflow.
• Schedule Professional Tune-Ups: Have your AC system inspected and tuned up by a professional once a year.
• Keep Condenser Fins Clean: Ensure the condenser fins are clean for optimal performance. Use a soft brush or fin comb to remove any debris.

Conclusion

Checking your AC compressor doesn’t have to be a daunting task. By following these detailed steps, you can diagnose common issues and potentially save on costly repairs. Remember, safety is paramount, and when in doubt, always consult a qualified HVAC technician. Regular maintenance and prompt attention to problems will keep your AC system running efficiently and reliably for years to come. Hopefully, this guide has helped you on your journey to diagnose and address your AC compressor issue.