How to Test an RV Air Conditioner Capacitor

Having a working air conditioner is crucial for comfort when RVing, especially in the hot summer months. If your RV air conditioner isn’t blowing cold air, one of the first things to check is the capacitor. Testing and potentially replacing the capacitor is an easy DIY repair that can get your A/C back up and running.

What is an AC Capacitor and What Does it Do?

The AC capacitor is a small can-shaped part that stores electrical energy for the air conditioning system. It works with the compressor motor and fan motor to start the unit and keep it running smoothly.

Specifically, the capacitor gives these motors the jolt of energy they need on startup. It also helps stabilize voltage so the motors run properly without overheating or drawing too much current. Without a working capacitor, the A/C won’t turn on or will struggle to stay on.

RV air conditioners have either a dual run capacitor or a separate start and run capacitor. Dual run capacitors operate both the compressor and the fan motor. Units with separate capacitors have one for starting the compressor motor and another to run the fan motor.

Signs You Need a New Capacitor

Here are some common signs that the AC capacitor may be bad and in need of replacement:

  • AC won’t turn on – If the air conditioner doesn’t start when you flip the switch, the capacitor could be failed. This is the most obvious symptom of a bad capacitor.
  • AC turns on but shuts off after a short time – If the A/C starts but then quickly shuts off, the capacitor may not be providing enough sustained energy to the motors.
  • AC blows fuse or trips breaker – A failed capacitor that isn’t starting the motors properly can cause the air conditioner to draw too much current and trip the fuse or breaker.
  • AC makes humming/buzzing noise but won’t start – You may hear a humming or buzzing sound coming from the unit when you turn it on. This indicates the capacitor is trying to start the motors but can’t quite get them going.
  • AC runs but air flow is weak – With a bad capacitor, the fan motor may run slowly, causing reduced air flow through the vents.
  • AC runs but isn’t very cold – Faulty capacitors can lead to refrigerant flow issues that prevent proper cooling.

Any of these symptoms point to a capacitor that needs replacement. Testing it is the next step.

How to Test an RV Air Conditioner Capacitor

Testing an RV AC capacitor is a fairly simple process you can do yourself without any special tools:

1. Turn Off Power to the AC

  • Shut off the breaker for the air conditioning unit. This is crucial for safety when working on electrical components.

2. Remove the Capacitor

  • Open the external AC unit by removing the plastic cover.
  • Locate the capacitor, usually mounted near the compressor. Dual run capacitors have 2 terminals, while start/run capacitors have 3.
  • Note which terminal connects to which wire for proper reinstallation.
  • Discharge the capacitor by shorting the terminals with an insulated screwdriver. This releases any stored energy.
  • Remove the wires from the capacitor.
  • Unmount the capacitor from the frame and remove it.

3. Check Capacitor Rating

  • The capacitor rating (capacitance and voltage) should be printed on the side. Make note of this for reference.
  • If no rating is visible, the capacitor is likely bad and will need replacement.

4. Use a Multimeter to Test Capacitance

  • Set a digital multimeter to the capacitance setting, usually denoted by “nF” or “uF”.
  • Touch the multimeter probes to the capacitor terminals. It doesn’t matter which probe connects to which terminal.
  • The capacitance reading on the multimeter should be close to the microfarad (uF) rating printed on the capacitor.
  • If the reading is significantly lower than the rating, the capacitor is bad and should be replaced.

5. Use a Multimeter to Check for Continuity

  • Set the multimeter to continuity or ohms setting, signified by the Ω symbol.
  • Touch the multimeter probes to the terminals.
  • A good capacitor will show an open circuit, while a bad one will show continuity between the terminals.
  • If the multimeter beeps or shows zero ohms resistance, the capacitor needs replacement.

6. Use a Multimeter to Check ESR

  • “ESR” stands for equivalent series resistance. This tests the internal resistance of the capacitor.
  • Set the multimeter to the ohms setting again.
  • Touch the probes to the capacitor terminals and note the resistance reading.
  • Consult the manufacturer’s specs for acceptable ESR range. Generally, more than double the spec ESR indicates failure.
  • High ESR means the capacitor should be replaced.

7. Reinstall or Replace if Needed

  • If the capacitor tests indicate it’s bad, install a new one of the same capacitance and voltage rating.
  • If the capacitor checks out good, reinstall it in the same terminals and position.
  • Restore power and test operation of the AC.

Following this straightforward capacitor testing process allows you to determine if replacement is required and avoid the cost of replacing other working parts like the motor.

Safely Discharging and Disposing of Capacitors

Capacitors contain stored electricity that needs to be properly discharged before removal to avoid shocks or sparks. Here are some tips for safe handling:

  • Always turn off power to the AC before accessing the capacitor.
  • Use an insulated screwdriver to short the terminals and discharge completely.
  • Store spent capacitors in a plastic bag or wrap in insulating tape before disposal.
  • Wear safety glasses in case of bursts or explosions from faulty capacitors.
  • Check local regulations – some capacitor types require special hazardous waste disposal.

Use extreme caution when working with capacitors, as they can retain high voltage charges even after power removal.

RV Air Conditioner Capacitor Replacement Cost

If you do need to replace the capacitor, the part itself is relatively inexpensive. Expect to pay around $20-60 for most RV A/C capacitors. The specific cost depends on the capacitor rating and brand.

The main cost for replacement comes from labor if you can’t do it yourself. RV repair shops charge $150-250 on average for the service call, diagnosis, part cost, and installation.

Doing it as a DIY project can save a good chunk of change. Just be sure to take the proper safety precautions and don’t hesitate to call a professional if you’re unsure about tackling it yourself.

Selecting the Right Replacement Capacitor

It’s important to match the new capacitor’s specifications precisely to the original. The key details to look for are:

  • Capacitance – rated in microfarads (uF)
  • Voltage – rated in volts (V)
  • Frame size – physical dimensions described in a code like “150550V452P10”
  • Terminals – number of terminals and position

Ideally, purchase an exact OEM replacement part made specifically for your AC unit. Check the capacitor ratings carefully before purchasing a generic unit.

Dual run capacitors and start/run capacitors cannot be interchanged. You must replace with the same style of capacitor that was originally in the A/C.

Using an incorrectly rated or wired capacitor can cause more damage to the air conditioner. When in doubt, have a technician match and install the right capacitor.

Troubleshooting RV AC Issues Beyond the Capacitor

While a failed capacitor is a frequent culprit, other problems can also cause an RV AC to malfunction. Here are some things to check if replacing the capacitor doesn’t resolve the issue:

  • Power Supply – Check for voltage to the unit at the breaker. Low voltage from the RV hookup can prevent proper operation.
  • Fuse/Breaker – Verify the fuse or breaker is sized appropriately and not tripping.
  • Wiring – Inspect wires to the AC unit for damage or loose connections.
  • Fan Motor – If the fan doesn’t run with a good capacitor, the motor may be burned out.
  • Compressor – If the compressor doesn’t run, it could have an internal mechanical failure.
  • Refrigerant Level – Low refrigerant affects cooling ability and puts strain on the compressor.
  • Thermostat – Make sure the thermostat is set properly and functioning.
  • Condensate Drain – Clogged drains can cause the AC to shut off due to high water pressure safety switches.
  • Unit Air Flow – Ensure coils and filters are clean and fans run freely without obstruction.

AC repairs beyond the capacitor may require an HVAC technician to diagnose and service. Proper capacitor testing and replacement is still a wise first step before getting into more complex issues.

Signs It’s Time to Replace the Entire AC Unit

In some cases, an RV air conditioner suffers catastrophic failure of the compressor or has extensive electrical damage. Repairing these issues can exceed the cost of installing a new AC unit.

Consider complete AC replacement or upgrade if:

  • You’ve already replaced the capacitor and other parts, but problems persist.
  • The compressor makes loud knocking or scraping noises.
  • Leaking refrigerant and oil is found around the unit.
  • Coils are rusted or damaged from leaks.
  • Electrical shorting or burned wiring is present.
  • Parts are obsolete or difficult to source.
  • Efficiency upgrades are desired.

Consult an RV AC specialist about replacement options if repairing the existing unit is no longer feasible. Properly maintaining the capacitor and other components can maximize the lifespan of your RV air conditioning. But units do wear out over time, especially if leaks or electrical issues develop.

Frequently Asked Questions About RV AC Capacitors

Here are answers to some common questions about testing and replacing air conditioner capacitors in RVs:

How often should I test the AC capacitor?

It’s a good idea to test the capacitor every year prior to summer cooling season. Catching a failed capacitor early can prevent bigger issues down the road.

Why did my new capacitor fail quickly?

Getting a bad new part does happen on occasion. More often, incorrect sizing or installation causes early failure. Always double check ratings and connections.

Can I upgrade my RV air conditioner capacitor?

It’s generally not recommended to use a higher capacitance than the OEM spec. Better efficiency is unlikely, and it may increase strain on the motors. Stick to the same microfarad rating.

Do I need to discharge a capacitor before testing?

Yes! Failing to discharge the stored voltage in a capacitor prior to removal risks dangerous shocks or sparks. Always ground the terminals first as a safety precaution.

My AC capacitor has green crud – is that bad?

Green corrosive buildup around the terminals is a sign of capacitor failure and the need for replacement. Do not continue using a capacitor with this leakage.

What size capacitor wrench do I need?

If your capacitor has a hex mounting nut, use a 1/2″ or adjustable wrench to remove it. Needle nose pliers can grip the terminals when removing wires.

Can I temporarily wire the AC to run without a capacitor?

Do not attempt to operate the air conditioner without a properly sized and installed capacitor. This will likely cause permanent motor damage.


Having an RV air conditioner fail in hot weather is not an ideal situation. By routinely testing and replacing the capacitor as needed, you can avoid being stuck with no cooling. Follow the step-by-step instructions to check your capacitor. Identify any telltale signs it needs replacement. With the right safety precautions, it’s an easy repair you can handle and get back to enjoying your RV adventures.

Key Points

  • The capacitor provides startup voltage and stabilizes current for the compressor and fan motors. Without it, the AC won’t work properly.
  • Symptoms of a bad capacitor include AC not starting, short cycling, blowing fuses, making humming noises, loss of cooling, etc.
  • Use a multimeter to check the capacitance, continuity, and ESR of the capacitor against manufacturer specs to test function.
  • Match the new capacitor’s capacitance rating and voltage exactly to the original capacitor.
  • Improper sizing of the replacement capacitor can cause additional AC damage.
  • Beyond the capacitor, other issues like refrigerant leaks, electrical shorts, and clogged drains may require an HVAC technician.
  • Consider replacing the whole AC unit if the compressor is seized, coils are leaking, or there is significant electrical damage.

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