Saturday, September 30, 2023


Why can’t I recharge my RV’s roof air conditioner like truck or house A/C?

Dear Dave,
Why is it that I can add refrigerant to my truck A/C and to my house A/C but not the rooftop A/Cs on my RV? When it runs out of Freon (or its equivalent), I have to replace the entire A/C, costing roughly $2,000. Makes no sense to me, but I’m sure I must be missing a key point here. —Yony, 2018 Keystone Montana 3791RD

Dear Yony,
That is a very good question and one that I could not get a very good answer for when I posed it to several techs at the air conditioning manufacturers. The refrigerant starts in a gaseous state in the compressor and is pressurized, which turns it into a liquid state. It is forced through the copper pipe and turns back into a gas in the evaporator. This process is typically called “flashing” and it pulls heat from the interior air that has been drawn in by the fan. It then flows back to the condenser, where it starts all over again.

According to Dometic, they use a high-performance motor and fan to deliver powerful cooling performance using a more eco-friendly R410A refrigerant.

Probably the best answer I got from one technician is the pressure in the line is too high for any port to be safely installed, and most roof air conditioners have a separate issue rather than low coolant. In the majority of cases when the unit was recharged, it was very expensive and did not fix the issue. More often it is the compressor that gets weak due to a high amp draw caused by a dirty filter or other air flow restrictions such as dust and pet dander blocking the evaporator.

But the internet says you can!

I did a Google search and found listings both ways. Most of the articles that stated you can recharge or refill were obviously written by artificial intelligence (AI) and the information was mostly wrong. Some stated there was a factory installed port, which is not true. Others indicated it was easy to cut the line and tap in a fill port. A tech from a different air conditioner company stated that this would void any warranty and may even cause serious damage to the unit. Copper is a soft metal and not easy to reweld and hold such high pressure.

I did find several posts that stated they had successfully tapped into the system and recharged it; however, none of them had an update on how well it worked over time.

I also talked with my RV Repair Club tech that was in charge of appliance repair at Winnebago for more than 15 years. He stated that although they did not try this on new units due to warranty, most attempts on used units at Customer Service either did not work or did not last. They ended up not trying it after several reworks that were required.

 You might also enjoy this from Dave 

Dometic A/C keeps changing fan speeds. Why?

Dear Dave,
My RV’s main Dometic A/C unit will sometimes keep changing fan speeds. It sounds like the compressor hesitates and starts with the fan speed being higher or lower. This will continue for some time, or I can raise the thermostat temp to stop it. Is this normal or could it be a bad thermostat? The internet has all kinds of misinformation. —Carl, Keystone Cougar MKS333

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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1 month ago

Today I sprayed out my condenser on the roof (didn’t really need it) and noticed a couple of interesting things. 

For this Coleman Mach 3+ 8333B SERIES (2006 model year), the spec plate says “Design pressures: High side: 300 psi, Low side: 150 psi.” So this confirms that RV roof units are pretty high pressure compared to fridges.

I looked over the unit carefully and did not see any hint of a fill port. Everything is soldered up solid. So it appears that by 2006 at least some manufacturers were not including a fill port. 

Last edited 1 month ago by John
2 months ago

They don’t put ports so a/c can be recharged for MORE PROFITS. they sell a lot more a/c units when you have to buy a new a/c unit than if you could recharge it. PURE GREED.

2 months ago

RV ac units are built to the same standards as cheap window air conditioners. They were not designed to have the system opened and repaired. That said, I have repaired window ac units in the past and there is no reason why these can’t be repaired with the proper refrigerant, access valves, drier, and brazing equipment.
If a leak is in the coil, it probably isn’t worth the hassle of trying to repair it.
And for the record, “Freon” is a trade name (DuPont) , like Xerox, or Google.

2 months ago

Our RV, a 2021 model has one A/C unit that has shot craps. Guess who the manufacturer is? (hint: starts with a D). I’ve come to the conclusion that one of the causes of poor quality in the RV world is the grouping of manufacturer’s in Indiana and the satellite grouping of suppliers in that area. Of course they could build units with charging ports. Or, surprise, surprise, build them with enough quality to work for 10 or 15 years.

Justus Wunderle
2 months ago

My dometic air conditioner unit on the travato broke with not much usage. The copper lines going in and out of the compressor fatigue and cracked. I replaced them and added ports. This worked but I don’t know how long it’s going to last because the compressor oil is largely hygroscopic and if the system is open will be spoiled. It is difficult to totally clean the entire system so we shall see

Steve Hericks
2 months ago

I formerly managed a custom A/C manufacturing company and was the plant engineer for Safari Motor Coaches.

In any refrigerant system, if the failure symptom is low refrigerant, the cause is a leak. Finding the leak can be a challenge especially if it’s in one of the coils. Fixing the leak involves removing the refrigerant (special equipment), flooding the circuit with inert gas (more equipment), brazing the leak closed (more equipment), replacing the refrigerant line dryer (more brazing and a part), evacuating the system to a hard vacuum (more equipment), retesting for leak integrity and recharging the system. Time, equipment and materials will most often exceed replacement $.

2 months ago

This article leaves me with more questions. I have three rooftop ACs on my current 2017 motor home. I replaced one within the warranty period due to overcurrent of the compressor. I replaced another when the refrigerant leaked out. I have repaired the 3rd one twice (faulty redundant pressure switch and broken squirrel cage blower wheel).

Out of all the AC failures, how many are due to dirt? How many are due to ‘value’ engineering? Like in so many other issues, the real answer probably lies with ‘follow the money’. Anything else is obfuscation.

Thomas D
2 months ago

If it needs freon, it more likely to have a leak. Finding and fixing that leak is next to impossible if it is in one of the coils with all the aluminum fins on them. And more and more manufacturers are using aluminium tubing. So welding isn’t an option. I installed a lot of charging ports by silver soldering. They’d work but again, any leak and recharge. Cars are different because the compressor is driven by a rotating pulley and has a seal that could and usually does leak. A completely different animal.

2 months ago

410A or known by another name “Puton” has been around for a very long time. The system does run at a higher pressure however fill lines are on the low side however their usually is a port to monitor the high side. When filling with 410A we would draw down the vacuum lower than we would with other gasses to remove as much moisture and would leave the vacuum pump on longer to accomplish it. The size of the rooftop systems is very small and a technician needs to be on top of his game so to not overcharge it, that being said a small car also has a very small system and recharging is routinely accomplished. I do not know how they charge the systems at the factory without fill ports.

Tom Penn
2 months ago

Dave may have over-simplified the refrigeration cycle. Once the refrigerant (Air conditioners don’t use “coolant”, they use refrigerant) passes through the evaporator it is a low pressure gas. Systems are always charged at the low pressure side when they are running.

Rod B
2 months ago

My 15K a/c stopped blowing cold air so I called a mobile tech that I had used before. He found a small crack in one of the lines and proceeded to silver solder the leak and install a line tap and recharge it. That was over 3 years ago and it is still working great. We use our motorhome 6 to7 months a year so it does get used as we also use the heat pump cycle in cooler weather. The cost was 1/5th the price of a new unit.

2 months ago

I call foul on the reason being “ the pressure in the line is too high for any port to be safely installed,”. The question was why don’t manufacturers install the valves? On the factory floor, they would be amiss if they waited until the unit was filled with freon to do so. It’s greed, plain and simple.

2 months ago

Any refrigerant system can be recharged. The RV ac industry intentionally doesn’t install recharge ports to keep the cost of the unit down and to encourage replacement rather than service. They can be easily recharged if the compressor and other components are still good. false media hype is all over the place, nothing new there….

Steve Hericks
2 months ago
Reply to  roy

Completely agree.

2 months ago

How did you determine it was low on freon? If you need to add freon you have leak. Probably should fix the leak first.

2 months ago
Reply to  Michael Roach


2 months ago

My first question for Yony is why did you pay 2000 dollars for a replacement. You can buy them for 6-800 dollars all day long and only take 30 minutes to install?

Richard McAlpine
2 months ago

I did put a line tap into my roof AC 5 years ago when it was not performing that well in the hot Florida summer. To this date the AC is working great. I believe the AC in your house and the AC on the RV is made with the same copper lines. The reason they are NOT refillable from the factory is because it generates more income for the company…. Any good AC tech can install the proper part to make these AC refillable/rechargeable.

Bob M
2 months ago

I’ve read Richards comments before. I believe they would use silver solder to attach the freon fitting. I believe a new A/C unit is more expensive that Brandon indicates. Everything went up after the pandemic. Because of the size and weight it might be difficult for one person to install. Plus you have the issue of getting it on the TT roof.

Tommy Molnar
2 months ago
Reply to  Bob M

Valid points, Bob.

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