Duo Therm RV Air Conditioner How to and Troubleshooting Guide

If you have ever spent a hot summer in an RV, you understand the importance of having a good air conditioner in the RV. The Dometic Duo-Therm air conditioner is a pretty good match for a hot summer. Below are some tips to help you troubleshoot and remedy any potential issues.

Duo Therm RV Air Conditioner Not Working

Below are some reasons why the air conditioner is not working and how to fix them.

Faulty Power System

When the RV AC is not turning on, you will need to find out if it gets the power supply. An interrupted power supply will prevent the air conditioner from working. Inspect the 12V panel to see if the fuse is blown or the breaker is tripped. The thermostat also draws power from the same panel. If the thermostat also does not work, you can change or repair the power panel.

Tripped Circuit Breaker or Power Panel.

If it is a blown a fuse or a tripped breaker, you have to change or reset the breaker. It may happen when the power supply of your campsite is too weak to power up the AC system.

However, this is not a problem in the campgrounds as they use a 50A service for modern AC systems. However, it could happen in the sites that still use the old 15A power poles.

Lastly, check the breaker as it can trip for some other reasons. If the power system is working fine, you have to check some other components.

Wiring Issues

The wires that run from the AC unit to the power outlet could be another reason the RV air conditioner won’t turn on. If this is the case, you should contact a professional HVAC mechanic to handle the issue. Dealing with frayed or dead wires could be tricky and dangerous.

Faulty Motor or Compressor

The whole system will shut down and won’t start if the motor is malfunctioning. So you need to check the motor to see if the issue is repairable or you need to replace it. Similarly, problems with the AC compressor may cause the whole system to shut down.

Defective Thermostat

Another reason the RV air conditioner won’t turn on is the faulty thermostat. It is defective if touching its wires to each other turns on the AC system. In the case of a wall-mounted thermostat, use a multimeter to check its voltage.

However, you should examine the AC system’s control board if both thermostat and capacitors are functioning. Even if the thermostat is defective, you can easily replace it. But changing the AC unit’s control board is more complicated and requires professional expertise.

A failed capacitor or contactor is the reason RV AC clicks but won’t turn on. If this is the problem, always hire a professional to do the repair work. Capacitors store high-voltage power, and there is a chance to get electrocuted if you attempt any repair.

Dirty Components

Dirt build-up in several components, including filters, evaporators, and the condenser, is one of the leading causes of AC system breakdown. Regular servicing and cleaning is an effective way to avoid this problem.

Low On Refrigerant

An air conditioning system won’t work if it is low on refrigerant. Even if it turns on, it is unlikely to function correctly. It will be easier to refill if your AC unit uses R410A or R-134A refrigerant rather than the R-22 types. You should ask for professional help for the refill.

Even the most reliable air conditioning system can show trouble. But buying from a renowned brand with good reviews ensures that you will get good service and will be covered with a warranty if the unit breaks down.

Duo Therm RV Air Conditioner Keeps Cycling On and Off

Short cycling is one of the main problems one can experience when it comes to AC issues. Below are the leading causes of AC short cycling;

Connection Issues

If there is a loose or burnt connection, it will arc and turn hot, which may cause the on and off the problem. Such a connection transmits enough power to run the fan but not enough to power up the compressor.

The whole system shuts off whenever the compressor comes on. This problem needs to be addressed as soon as possible because it risks damaging the system components or becoming a fire hazard.

Faulty Thermostat

The thermostat is set to the ‘Automatic’ mode, and it is supposed to work fine without any intervention. However, the RV air conditioner turns on and off repeatedly when the thermostat does not function properly.

Failing Control Board

A malfunctioning control board can also cause the same symptoms. If you suspect that the control board is the culprit, consult a certified RV technician to diagnose the problem.

Dirty Air Filter

Dirty air filters can cause a multitude of problems with air conditioners. When an air conditioning system’s filter is dirty or clogged, there is not enough fresh air coming through, and your system might overheat. This overheating will shut off the air conditioner before a complete cycle ends.

You may be able to tell if a dirty air filter is to blame. Uneven cooling in the RV can be an indication that it is time to change your filter. Also, poor airflow can cause cold air to become trapped inside the air conditioner unit. This can cause ice to form on the coils.

Frozen AC Evaporator Coils

If the on and off-cycle occurs mainly at nights or on humid days, it could be because of frozen AC evaporator coils. There are two ways to unfreeze them: running the system in the ‘Fan Only’ mode or keeping it off until the coils are back to their normal state.

However, these are only temporary solutions. A permanent solution to this freezing problem will be to operate the air con at a higher temperature. Another way is to change the filter and make sure there is no build-up of dirt in the coils.

Faulty Capacitor or Compressor

Aside from the issues mentioned above, short cycling can also be caused by a malfunctioning start capacitor or a bad pressure switch on the compressor.

You have to be careful when diagnosing the RV air conditioning system. The upper part of the system always carries substantial voltage even after unplugging from the electrical outlet. Touching that part without wearing insulated gloves can cause serious injury.

Duo Therm RV Air Conditioner Not Blowing Air At All

Below are a few reasons why your air conditioner is not blowing air and their prospective solutions.


Several air conditioner components can get clogged with dirt and other materials, causing the RV air conditioner not to blow cold air. Such as; dirt, spider webs, and other things that can get into the condenser coils and clog fins.

Check this too: How to Keep RV Pipes from Freezing When Camping

Clean it and check the foam filter in the intake grate to see if it is clean. A soap and water mix is enough to clean the foam filter, but you have to change it if it’s a couple of years old.

Dirt and grime can jam the evaporator and blower motor fins and obstruct the cold air streaming. If there is a leak outside the blower box, use foil tape to seal it.


A small hole in any of the components can affect the flow of cold air. Leaks in AC intake and exhaust can cause all sorts of trouble. If wires are poking through the duct of AC intake, seal them up with foil tape so that hot air does not leak into the intake.

If the exhaust ducts and roof seal wears off, cool air will blow around the vents and into the hot roof instead of inside the trailer. You have to close the gaps by using weather seal foam.

The air from intake and exhaust could get mixed if the foam ring in the splitter wears out. Use weather seal foam and foil tape to close out any opening.

Dirty Compressor

Dirt can get into the compressor too and prevent its normal operation. Your RV’s regular maintenance schedule should include cleaning the areas around the compressor. If you leave the RV in the garage for a long time, don’t forget to cover the whole AC unit.

You can clean it by yourself, but taking professional help will be the best practice. Remember to switch the AC off before starting the cleaning task.

Malfunctioning Safety Switch

Some air conditioner models feature an inbuilt safety float switch. If the condenser drainpipe overflows with water, this switch trips and turns off the system. If this is the case, clean the drainpipe and then reset the switch.

Hot Weather

Heat gain inside the trailer is another reason for the air conditioner to blow cold air. Most RVs don’t have good insulation because extra-thick walls will eat up the living space. For example, there won’t be much room left if the vehicle has 6-inch thick walls all around.

If you park the RV directly under the sun in scorching weather, the heat inside the vehicle will be greater than the AC can pump back out. The solution is parking the RV under a shade like a tree or an awning. Just keep your trailer out of the way of direct sunlight.

Duo Therm RV Air conditioner Not Cooling

The main reason for having an air conditioner is to cool the RV during the hot summer months. Below are some reasons why your air conditioner is not blowing cold air;

Incorrect Set Thermostat

Check your thermostat settings and make sure it’s set to cool and not to blow hot air. If your thermostat is set to cool, check the temperature and see if it has been changed.

If it has been turned off or set for a constant fan, switch it back to the cooling operation. Once your system kicks in, wait a few minutes, and check you have cold air blowing rather than warm air. If it’s cold, you have resolved the problem.

If your air conditioner is not blowing cold air now, carry on with the fixes below or check the relay board.

Dirty Air Filters

Your RV AC unit could include air filters situated in or around your indoor air handler unit. The filter’s job is to catch dirt and other airborne particles before entering the air handler unit. Doing this keeps the components of the system working and staying clean.

A dirty air filter can block cool air airflow and reduce cooling, or it could lead to your AC system shutting down. You can clean your filer weekly with soap and water to fix this issue.

Condenser Unit is Blocked

Your air conditioning system has outdoor condenser coils. The exterior of your condenser unit will have a large coil that wraps around the outside of the unit. The coil includes the thin metal “fins” that help cool the unit.

If your RV air conditioner is running but not cooling, you could have a blocked or clogged condenser coil. The condenser fan draws air into the unit through the condenser coil and pulls heat from your RV when correctly working.

Damaged Heat Pumps

In some cases, an outdoor unit could include a heat pump. These appear to be like an AC unit but with different components to let them cool and heat your home.

In cooling operation, they work like an AC’s condenser unit and are subject to the same issues such as dirty, clogged coils, frozen, or refrigerant leaks, among others.

If your heat pump system doesn’t cool, check the thermostat, air filter, and condenser unit for the above. If all these are okay, you may need an AC specialist to repair your RV AC.

Frozen Evaporator Coil

The indoor side of your central air conditioning system includes an evaporator coil. Warm indoor air will pass through the evaporator coil as heat and humidity are removed from the air. Cooler air is then circulated back to your RV.

Refrigerant Leaks

Refrigerant is vital for the cooling process as it changes from a liquid to a gas, draws heat energy and humidity from indoor your RV’s air, and pushes it outside.

The extent of a refrigerant leak could contribute to an AC system not blowing cold air. As a result, your system may run for more extended periods without adequately cooling your home, or it can cause a damaged or failed compressor and complete system shutdown.

Duo Therm RV Air Conditioner Compressor Not coming On

There can be various reasons why an air compressor fails to come on;

Malfunctioned Starting Compressor

A malfunctioning starting compressor is usually the main culprit. Ensure you check the compressor before buying an air conditioner. Also, buy from manufacturers that have a warranty on them.

Dirty Filters

If dirt builds up in the coils and filters, it can cause the unit to shut down. Moreover, a clogged-up filter can reduce airflow in significant amounts. As a result, the coil of the evaporator stops working.

As if that’s not enough, these dirty filters can cause the compressor to overheat. This is because it constantly puts pressure on it. Hence, the compressor shuts down and doesn’t come up.

Dead Compressor

This can happen when a compressor gets under too much pressure and eventually burns out. In addition, an overheating compressor will prevent the air conditioner from working.

Capacitor and Relay Problems

The relays are responsible for the supply of power in the compressor. But, on the other hand, they’re also the cause of many problems with the compressor.

Again, the capacitors also provide power to run the compressor and the fans. When the problems occur in the capacitor and relays, the compressors shut down and don’t start.


Many times, the compressor won’t start because the power isn’t enough in the outer unit. As a result, the blower and several significant parts of your RV are affected due to insufficient power. However, the fans usually run as the central unit has power in it.

Check this too: How to Watch TV in an RV Without Cable

How to Fix a Malfunctioning Air Conditioner

Follow the steps below to

Tools Needed;

The tools that you’ll need for the job are affordable and available. Also, you can buy them from the local markets or online. So let’s take a look at them:

  • Multimeter.
  • Testing Relays.
  • Power Wire.
  • New Compressor.

Check Power

Firstly, check whether your compressor is getting enough power in it. This is because burnt fuses can easily cause your compressor to stop working. So, if you can make sure the compressor has enough power in it, it can start working again.

If the fuses are OK, call in a professional. However, if you want to do it yourself, check if the compressor’s voltage is right. Even though you can do all these things on your own, you can still call up a technician to check if it’s right or not.

Check the Start Relays and Capacitors

A broken capacitor can cause a compressor not to turn on. So, if that’s the case, you can replace it with a new one. On the other hand, you can replace start relays easily as well without much of an inconvenience.

The best thing about these two fixes is that they don’t cost much and you can get them replaced quickly. Also, check the capacitors using a Multimeter and the start relays using a Tester Relay.

Check the Terminal Connections

Loose connections can cause problems. Like, the main battery disconnect switch troubleshooting or any other wiring issues are standard. But, first, check whether the terminal connections are tight and in place. This could resolve the problem, too, if you had loose connections before.

So, you can quickly check them using the power wires. If you don’t have these tools before, purchase them online.

Replace Compressor

If the compressor is completely dead and won’t start, then you’ll have to change it. Even though it’s quite an expensive option to take, it’ll still be worth it in the long run.

How to Clean Your Duo Therm RV Air Conditioner

Follow the steps below to clean your AC filter;

  • Power down any connections and shut off the air conditioner
  • Decide whether you want to clean it yourself or hire a technician
  • Open the cover and remove the filter
  • Note the manufacturer make and model
  • Do not reactivate the AC without the filter
  • Scrape clear dust and other particles with a microfiber cloth for light clean or coarse brush for grease and grime
  • Use a vacuum to clean fine particles, be careful with the pressure
  • Submerge in warm, soapy water for no longer than 30 minutes
  • Remove and rinse
  • Treat with half parts vinegar, half parts water to prevent microbial growth
  • Dry with a towel, set in a warm place (preferably the sun)
  • Replace cleaned, dried filter into the unit

How to Clean The AC Evaporator Coil

Start by shutting off all power and disconnecting the battery. The air conditioner unit will have two coils, the condenser, and evaporator. The condenser is located in the back and can be seen without opening the unit. The evaporator coil is in the front of the unit and is covered.

To clean the coil, follow the directions below;

  • Go to the roof where the air conditioning unit is located safely
  • Take off the shroud
  • Take off the coil sheet metal by removing screws
  • If the coil is wet, let it dry
  • When dry, clean with a vacuum
  • Put the unit back together

How to Maintain The RV AC unit

RV air conditioners are no different than any other appliance that requires regular maintenance. The four key areas you need to focus on include;

  1. Plastic Cover- it protects the air conditioner from the elements. Inspect it for cracks or splits
  2. Fan- maintain and service the fan to keep the air moving. It should also be well-oiled
  3. AC Condenser- check twice a year for dirt and leaves to prevent blockage
  4. Roof Vents- open the vents to allow moisture to evaporate

Note: ensure you have the appropriate tools and know-how to clean your RV’s air conditioning unit correctly. If you are looking to save money, DIY will ensure that you don’t spend extra hiring a technician.

That said, if you are not comfortable with cleaning or maintaining certain parts of the AC unit, you may want to hire someone with the appropriate certification.

How Much Power Does My Duo Therm RV Air Conditioner Need?

Air conditioners require a significant amount of energy to get started and to keep running. On average, an RV air conditioner requires a generator with a 2000- 4000-watt capacity. You will also need to use your AC and other appliances, even with a 2000-watt generator.

An air conditioner typically uses 1800 watts to start-up and roughly 500-800 watts to run. This means if you have a 2000-watt generator, you can run other appliances such as a laptop, refrigerator, and phone charger. But you may need a more powerful generator if you need to use other electrical appliances such as a coffee maker.

The key is to minimize power usage when possible. Below are a few dos and don’ts you can try to maximize your generator’s energy allocation to the AC.

  • Clean your filters and overall unit often.
  • Circulate the air in your RV by turning on the fan and not just turning the temperature way down.
  • Use some appliances during the evening or night, like charging phones or dishwashers, to balance energy usage.
  • Unplug the things you aren’t using. Plugged-in items like TVs will still consume energy even when they are “off.”
  • Don’t blast the AC on full power for short periods throughout the day. This will use more energy.
  • Don’t keep your AC unit running for long periods. It runs down the machine faster.

Note: Although a constantly running air conditioner fan can help battle allergies by keeping the air filter, it causes unnecessary wear on the motor and increases energy costs.

How to reset your Duo Therm Thermostat

  1. Turn the switch off.
  2. Press both the mode and the zone buttons while turning the switch back to On.
  3. As you are doing that, the letters FF should appear in the digital display and remain there until you release both the zone and mode buttons. Depending on your model, these letters could appear right away or in 15 seconds, give or take a few seconds.
  4. Hold the zone and mode buttons until these letters do appear, then release the buttons when they do. Your system should be reset and ready to work.

Duo-Therm Comfort Control Reset

  1. Turn the device on, and the light and annunciator data are there. If they are, move on to step 2 and if they aren’t, consult your manual section 5.1.
  2. Press the mode button to activate the annunciator light.
  3. Then, at the same time, press the up and down buttons and hold.
  4. Now, while the up and down buttons are still pressed, use another finger to press the mode button and release it immediately. You only need to press that button once at this time.
  5. When releasing the mode button, you can release the up and down buttons.
  6. Press the mode button again. Again, the light should go out, and the mode should say ‘off.’ If it doesn’t do the same steps all over again.
  7. Test the system to make sure the system reset and is working.
  8. When you see it is working right, re-program your settings to the levels you want.

Note: All previous program memory will be erased, and the controls will reset back to factory settings of 72 degrees F for cool air and 68 degrees F for warm air.

Duo Therm RV air conditioner not shutting off

The most common reason your Air Conditioner fan won’t turn off is that a stuck relay keeps the circuit closed. If it’s not the relay, your thermostat likely has a shorted cable or needs to be replaced.

Before calling your service technician out to start replacing components, try to see if it has other issues that are easy to fix.

  • Check the thermostat settings first.
  • Set the desired temperature above the current room temperature, so the air conditioner unit turns off
  • Double-check the thermostat and make sure the fan is not set to ON and that it still runs when switching it to AUTO or OFF.

If that does not work, the issue could be due to;

Stuck Relay

Relays in your air conditioner unit help open and close electrical circuits to turn components, like a fan, on and off. Over time, relays can fail or stick together from electrical currents, causing a course to stay closed and constantly supply power.

Malfunctioning Thermostat

A faulty thermostat can cause your AC fan to run constantly by not knowing when the desired temperature has been reached. If the actual room temperature is below what your thermostat is set for, there’s a good chance you’re due for a repair or replacement.

NOTE: the air conditioner units may be running nonstop to try and reach the desired temperatures. Often, these inefficiencies result from clogged or restrictive air filters, dirty or frozen evaporator coils, dirty or blocked condensers, or low refrigerant. Schedule an annual air conditioner tune-up to keep your system operating at peak performance.

Duo Therm Air Conditioner Not Blowing Hard

Weak airflow on a hot summer day can be a bummer. Below are some possible causes of weak airflow;

Dirty air filter

A dirty air filter prevents your AC from delivering enough air around your RV. Likewise, a clogged, dirty filter limits the amount of air your AC can pull in from your home.

Solution: Change the air filter if it’s dirty.

The filter is located behind the return grates or in a slot before the furnace/air handler unit.

Frozen evaporator coil

An AC cools the air by blowing it over the evaporator coil. If the coil gets too cold, its condensation will freeze, turning the coil into a big block of ice. The ice limits the flow of air into your home. Likewise, if the refrigerant line outside is also covered in ice, the evaporator coil is frozen.

Causes of a frozen evaporator coil include:

  • Low airflow over the coil is caused by a dirty filter, blocked return/supply vents, and a malfunctioning blower.
  • Refrigerant undercharge caused by a refrigerant leak.


  • Turn off the unit so that it has a chance to thaw the ice build-up.
  • Change the filter.
  • Open and unblock any supply vents and return grates.
  • Hire an AC tech to check your refrigerant level, evaporator coil, and blower.

Air duct issues

Air ducts carry air around your RV. Any issues with the ducts can limit the delivery of air around your home.

Possible air duct issues that can cause weak airflow include;

  • Leaky supply-side air ducts
  • Loose or disconnected ductwork
  • Flex duct has kinks or bends

Solution: Check your flex duct for any kinks or bends. Otherwise, you will need to contact an AC tech to examine your air ducts for issues.

Check this too: Carrier RV Air Conditioner How to and Troubleshooting Guide

Blower issues

The blower moves air around the RV.

Some blower issues can lead to weak airflow, including:

  • Dirty blower wheel
  • Loose or worn fan belt.
  • Faulty/malfunctioning blower motor