RV AC not cooling? Here's the fix.

Before you assume your AC is dying, check these seven things. Most "broken" RV air conditioners are actually starving for airflow or amps.

An RV air conditioner that runs but doesn't cool, freezes into a block of ice, or blows warm air is one of the most common summer calls mobile RV techs get. The good news: almost all of these are fixable without parts. This guide walks you through the exact checks in the order a tech would run them.

1. Are you actually getting enough amps?

An RV AC unit is a power hog. A 13,500 BTU unit needs a solid 15 amps just to run, and pulls 30+ amps at startup. If you're on a 30A pedestal, fine. If you're on a 15A household adapter or a small inverter generator under heavy load, the compressor will cycle weakly and barely cool.

Check your shore cord connection, the pedestal breaker, and any adapters in the chain. If you're on a generator, turn off everything else (fridge, converter, water heater) and see if cooling improves. For power cord issues, inspect for damage or melting near the connection points.

2. Clean the return air filter

This is the single most common fix. The return air filter is behind the plastic grille on the ceiling unit. Pop it off, pull the filter out, and look at it. If it's grey or brown, it's been choking your airflow for months.

Wash it with soapy water, let it dry, and reinstall. Or replace with a new one for $5. Do this every time you fire up the rig for the season. A clogged filter is the #1 cause of both weak cooling and frozen coils.

3. Inspect the outdoor condenser coil

Get on the roof with the AC off. Remove the plastic shroud (usually 4 or 6 screws). You'll see the outdoor coil, fan, and compressor. Look for cottonwood fluff, bug carcasses, leaves, or dust caked onto the fins. This blanket of gunk is making the AC work twice as hard for half the cooling.

Spray gently with a garden hose from the inside outward. Don't pressure-wash, you'll bend the fins. Let it dry completely before running the AC again.

4. Is the coil frozen?

If your AC was working fine and suddenly airflow dropped to nothing, look up through the return grille with a flashlight. If you see ice, the evaporator coil has frozen solid and the AC is blowing air through an ice block.

Turn the AC off and switch it to fan-only mode for 30 to 60 minutes to thaw. Then address the root cause: dirty filter, low refrigerant, or running with windows open in humid weather. A freshly thawed coil that refreezes within an hour means a refrigerant or sensor problem and needs a tech.

5. Check the thermostat

Some RV thermostats run on their own batteries (usually 2 AA). A low battery will let the fan run but won't engage the compressor relay. Swap the batteries and see if cool air returns.

Also confirm the thermostat is in AC mode (not Heat Pump, not Fan Only), the temperature setpoint is well below the room temperature, and the fan is set to Auto or High.

6. Listen for the compressor click

With the AC on and the temp set low, stand outside and listen to the rooftop unit. Within about 10 seconds you should hear a clear click-clunk as the compressor kicks on, followed by a steady hum that's louder than the fan alone. No click and no hum means the compressor isn't engaging.

The usual culprit is a blown run capacitor (a $30 part, 20 minute fix for a tech) or, worse, a seized compressor (needs a new rooftop unit, ~$1,000+). A tech can tell the difference with a clamp meter in five minutes.

7. Close every window and shut every vent

This sounds obvious but people forget. Every open window, vent, roof fan, and unsealed slide topper is dumping your cold air outside and letting hot air in. Close them all, pull blinds or shades on sun-facing windows, and give the AC 20 minutes to catch up.

If the rig was baking in the sun with everything shut for hours before you started, it can take an hour or more to pull the temperature down, no matter how well the AC is working.

Soft-start kits: running AC on 30-amp or generator power

If your AC compressor trips the breaker every time it kicks on, or if your generator can't handle the startup surge, a soft-start kit may solve the problem without upgrading your electrical system. Devices like the Micro-Air EasyStart or SoftStartRV reduce the compressor's startup amperage from 40 to 70 amps down to 15 to 25 amps. This means you can run a 15,000 BTU rooftop AC on a 2,800-watt generator or on a 30-amp shore power connection that used to trip. Installation involves wiring the module into the AC unit's compressor circuit on the roof. Most handy owners can do it in 30 to 60 minutes with basic tools. If your RV has two AC units, you'll need one kit per unit.

Dual AC setups and zone cooling

Many Class A motorhomes and larger fifth wheels have two rooftop AC units, one for the front living area and one for the bedroom. If only one zone is cooling, check that both thermostats are set correctly and that both units have clean filters. A common problem is running both ACs on a 30-amp connection, which does not provide enough power for two compressors. You need 50-amp service or a soft-start kit on both units. Some newer rigs use a ducted system that routes air from a single rooftop unit through ceiling vents. If certain vents blow warm while others blow cold, check for disconnected or collapsed ductwork in the ceiling. Flex duct can sag or get pinched during travel.

When to call a mobile RV tech

If you've worked through all seven checks and the AC still won't cool, it's time for a pro. Symptoms that mean "stop and call":

• Coil refreezes immediately after thawing
• Compressor clicks on and off every few seconds (short-cycling)
• Burning smell from the ceiling unit
• Breaker trips every time you start the AC
• Oil or refrigerant stains on the roof around the AC

Open Camphost and tell it your location, it will help you find mobile RV techs in your area.

Frequently asked questions

Why is my RV air conditioner running but not cooling?

Top causes in order: dirty return air filter (chokes airflow), dirty condenser coils on the roof (insulates the heat exchange), insufficient amps (15A adapter or weak generator), or a frozen evaporator coil. Clean the filter and roof coils first, those fix 70% of weak-cooling complaints.

How much can an RV AC actually cool the inside of the rig?

A single 13,500 BTU rooftop AC can pull the interior about 20°F below outside ambient. On a 100°F day, expect mid-80s inside. Two ACs or a 15K BTU unit can do better. Anything more requires shade, awnings, and reflective covers, the AC alone can't fight direct sun on a metal roof.

Why is my RV AC freezing up?

A frozen evaporator coil means too little airflow over the coil or too low refrigerant. Most common cause: dirty filter or running with windows open in humid weather. Turn the AC to fan-only for 30-60 minutes to thaw, then clean the filter and try again.

How many amps does an RV air conditioner draw?

A 13,500 BTU unit draws about 13-15 amps running and 30+ amps at startup. A 15,000 BTU draws 15-17 running. This is why a 15A household adapter can run the fan but barely cool, the compressor starves for amps. You really need a 30A pedestal or 3000W+ generator.

Should I run my RV AC on a generator?

Yes if the generator is sized for it. Onan 4000 and bigger handle one 13.5K AC easily. Smaller portable inverter generators (2200W) can run an AC only with a soft-start kit installed, which reduces startup amps. Without one, the gen will overload and shut down on AC startup.

Can I add refrigerant to my RV AC?

Most RV rooftop AC units (Coleman-Mach, Dometic Brisk, Advent) use a sealed refrigerant system that is not designed for field recharging. If the system is low on refrigerant, it means there is a leak, and simply topping it off will not fix the underlying problem. Some RV shops can locate and repair the leak, then recharge the system, but it is often more cost-effective to replace the entire rooftop unit. Residential-style mini-splits (found in some high-end rigs) can be serviced like home units by an HVAC technician.

How do I clean RV AC coils on the roof?

Turn off the AC and disconnect shore power. Remove the rooftop shroud (usually 4 to 8 screws). Use a garden hose with moderate pressure and a coil cleaning spray (like Nu-Calgon Evap Foam) on the condenser fins. Let it soak for 10 minutes, then rinse from inside out to push debris off the fins. Straighten any bent fins with a fin comb. While you are up there, clean the evaporator coil (the one facing down into the RV) the same way. Reassemble the shroud and let everything dry before restarting. Do this once a year or at the start of summer.

What size generator do I need to run RV AC?

A single 13,500 BTU rooftop AC needs about 2,800 to 3,000 starting watts and 1,200 to 1,500 running watts. A 15,000 BTU unit needs 3,200 to 3,500 starting watts. For two AC units, you need a generator rated at 5,500 watts or more. A soft-start kit can reduce the startup load, letting you run a 15,000 BTU unit on a 2,000 to 2,500 watt inverter generator. Most built-in Onan generators (4,000W and up) handle a single AC unit without issues.