RV AC Humming But No Air Flow? Fix It Yourself (2024 Guide)

Here's the Deal

Your 2006 Sightseer 30B air conditioner is experiencing what we call "compressor lock-up" after sitting unused for 13 months in storage. That loud humming sound with no airflow is a telltale sign that your compressor is trying to start but can't overcome the internal resistance that builds up when the system sits idle for extended periods. The compressor motor is drawing power and attempting to run, but the mechanical components inside have essentially seized or become extremely difficult to turn, creating that characteristic humming noise without any actual cooling or air movement.

This is actually a common issue with RV air conditioners, especially units that sit in storage for a year or more. Your Dometic or Coleman Mach unit (most likely what's on your Sightseer) has refrigerant that has settled, oil that has thickened, and internal components that may have developed some corrosion or sticky residue. The good news is that this doesn't necessarily mean your entire air conditioner is shot – many times these units can be brought back to life with the right approach. However, you'll need to act carefully because forcing a locked compressor to run can cause permanent damage to the motor windings.

What's Behind This

After 13 months of sitting idle, several things happen inside your RV's air conditioning system that can contribute to this problem. The refrigerant naturally settles to the lowest point in the system, which is typically the compressor itself. This creates an unbalanced condition where the compressor has to work much harder to get the refrigerant flowing again. Additionally, the compressor oil – which lubricates all the internal moving parts – tends to thicken and can even form a gel-like consistency in extreme cases.

The internal components of your compressor typically include rotating or orbiting elements in a sealed housing. When these parts sit motionless for months, several issues can develop:

• Corrosion on metal surfaces due to moisture in the system
• Oil that has separated from additives and lost its lubricating properties
• Refrigerant that has created pressure imbalances throughout the system
• Seals and gaskets that have dried out or become sticky
• Debris or contaminants that have settled on critical components

Your 2006 Sightseer likely has either a Dometic Penguin or Coleman Mach air conditioner on the roof. These units are workhorses, but they're not designed to sit completely idle for extended periods. The compressor is typically a rotary or scroll type, sealed in a steel housing with refrigerant lines running to an evaporator coil inside your RV and a condenser coil on the roof unit itself.

The electrical system is also a factor here. The compressor motor draws significant amperage on startup before settling down to normal running current. When the compressor can't turn freely, it continues to draw that high startup current, which is what creates the loud humming sound. This high current draw can also trip circuit breakers or damage the motor windings if allowed to continue for too long.

Getting Started

SAFETY WARNING: Before attempting any repairs on your air conditioner, you need to ensure your safety and gather the right tools. Turn off the air conditioner immediately – that humming sound indicates the motor is under stress and could overheat or suffer permanent damage if left running. Head to your electrical panel and switch off the breaker for the air conditioner to ensure no power is flowing to the unit. ELECTRICAL HAZARD: AC electrical systems can deliver fatal shocks. When using multimeters or working with electrical components, always verify power is off, use insulated tools, and never work on live circuits. CAPACITOR WARNING: Air conditioner capacitors store high voltage even when power is off and can cause severe shock. Discharge capacitors safely before handling.

ROOF ACCESS SAFETY: You'll need to access the roof-mounted portion of your air conditioner to diagnose and potentially fix this issue. Use proper safety equipment including non-slip shoes, a safety harness when possible, and have someone spot you when climbing. Ensure your ladder is on stable, level ground and maintain three points of contact at all times. On your 2006 Sightseer, this means safely getting onto the roof using proper ladder techniques. The roof unit will have a plastic shroud covering the internal components – this typically removes with 6-8 screws around the perimeter. Have these tools ready:

• Phillips head screwdriver and flat-blade screwdriver set
• Digital multimeter for electrical testing
• Note: Refrigerant system work requires EPA certification - contact certified technician for refrigerant-related issues
• Flashlight or headlamp for visibility
• Work gloves and safety glasses
• Camera or phone to document wire connections
• Basic hand tools including pliers and wire nuts
• Penetrating oil for fan motor bearings (compressors are sealed units)

Once you have the shroud removed, you'll see the compressor unit, fan motor, condenser coils, and electrical components. The compressor is typically a black or gray cylindrical or oval-shaped unit with refrigerant lines attached and electrical connections on top. Before touching anything, take photos of all electrical connections – this will be invaluable if you need to reassemble things later.

Check the obvious issues first, starting with the start capacitor - a failed capacitor is the most common cause of compressor humming without starting. Then look for any loose electrical connections, corroded terminals, or damaged wiring. Sometimes what seems like a compressor problem is actually a simple electrical issue. Inspect the fan motor as well – if the condenser fan isn't running, the compressor will struggle and may not start properly. The fan motor should spin freely when you turn it by hand with the power off.

Making the Repair

The first step in getting your compressor unstuck is to try the pressure equalization method. This involves giving the compressor time to equalize pressures and then attempting to start it under the best possible conditions. With the power still off, let the unit sit for at least 4-6 hours. This allows refrigerant pressures to equalize throughout the system, reducing the load on the compressor during startup.

After the waiting period, you can try what's called a "bump start." Turn the power back on and quickly turn the air conditioner on and off several times, with 10-15 second intervals between attempts. This can sometimes jar a stuck compressor loose. However, be very careful not to do this more than 4-5 times, as you risk damaging the motor windings from repeated high-current draw.

If the bump start doesn't work, you may need to manually assist the compressor. With the power off and the unit completely de-energized, locate the compressor. Some compressors have an external fan or pulley that you can carefully try to turn by hand to break them free. Be extremely gentle – you're not trying to force anything, just see if there's any movement available. If you feel any give at all, that's encouraging.

For compressors that are truly stuck, you might need to install a hard start capacitor kit. This is a common solution for RV air conditioners that have sat for extended periods. A hard start kit includes a starting capacitor and relay that provide extra torque to get the compressor moving. These kits cost around $25-40 and you'll need the correct part for your model (verify with dealer):

• Identify your compressor model number (usually on a metal tag)
• Purchase the correct hard start kit from an RV parts supplier
• Follow the included wiring diagram to connect the kit
• The kit typically connects to the compressor's start terminal according to the manufacturer's wiring diagram compressor's start and run terminals
• Test the system after installation

Another approach that sometimes works is the "refrigerant shock" method. This should only be attempted if you're comfortable working with refrigerant systems. The idea is to add a small amount of refrigerant to the system while it's trying to start, which can help break the compressor free. However, this requires refrigerant handling equipment and knowledge of proper procedures. If none of these methods work, the compressor may need professional service or replacement. procedures.

If you're getting some movement but the compressor still won't start reliably, check the run capacitor. This cylindrical component (usually mounted near the compressor) provides continuous power assistance to the compressor motor. A failed run capacitor can cause symptoms very similar to a locked compressor. Test the capacitor with a multimeter – it should read close to its rated microfarad value. A reading of zero or significantly lower than rated indicates a failed capacitor that needs replacement.

When testing electrical components, start with the basics. Check for 120V power at the compressor terminals with your multimeter. Verify that the thermostat is calling for cooling and sending the proper signals. Sometimes what appears to be a mechanical issue is actually an electrical control problem.

Call in the Pros

If the DIY approaches don't get your air conditioner running, it's time to bring in professional help. Several indicators suggest you need expert intervention rather than continuing to troubleshoot on your own. If you've tried the pressure equalization, bump starting, and checked all electrical connections without success, the compressor may have internal damage that requires specialized repair or replacement.

Professional RV technicians have tools and expertise that most DIYers don't possess. They can perform refrigerant recovery and recharging, which may be necessary if your system has lost refrigerant during the storage period. They also have specialized compressor testing equipment that can determine if the internal components are salvageable or if replacement is the most cost-effective option.

When calling for professional service, expect costs to vary significantly based on the actual problem. A service call and diagnosis typically runs $100-150. If the issue is something simple like a bad capacitor or electrical connection, total repair costs might be $200-300. However, if your compressor needs replacement, you're looking at a much more significant investment:

• Compressor replacement: $400-800 for the part
• Labor for compressor replacement: $300-500
• Refrigerant recovery and recharge: $150-250
• Additional components (drier, expansion valve): $100-200
• Total compressor replacement: $950-1750

Before authorizing major repairs, get a second opinion if the first diagnosis seems excessive. Some technicians might recommend complete unit replacement when a compressor repair would be sufficient. For a 2006 unit, you're at the point where replacement versus repair becomes an economic decision. A new roof air conditioner for your Sightseer runs $800-1200 plus installation, so if repair costs approach $1000, replacement might be the smarter choice.

Look for technicians who specialize in RV systems rather than residential HVAC. RV air conditioners have unique characteristics and requirements that general HVAC techs might not fully understand. Many larger RV dealerships have service departments that can handle this type of repair, and mobile RV repair services are increasingly common in most areas.

Prevention is always better than repair, so once you get your system running again, maintain it properly. Run the air conditioner at least once a month, even during storage, to keep the compressor lubricated and prevent this type of lockup. Consider having the system professionally serviced every 2-3 years to maintain refrigerant levels and replace aging components before they fail. With proper maintenance, your RV air conditioner should provide many more years of reliable cooling service.