Saturday, September 23, 2023


Ask Dave: What can be done about two AC units that are behaving badly?

Answers to questions about RV Repair and Maintenance from RV expert Dave Solberg, author of the “RV Handbook” and the managing editor of the RV Repair Club. This column appears Monday through Saturday in the RV Travel and RV Daily Tips newsletters. (Sign up for an email reminder for each new issue if you do not already receive one.) Today Dave discusses rooftop AC units.

Dear Dave,
Why do my two rooftop air conditioners freeze up and one spits out ice and the other drips on my bed? We live in our 5th-wheel trailer full-time in Louisiana. Is there anything that we can do? I called Camping World, where we purchased it used in December, and the man said to turn the fan on high. It hasn’t helped. —Cynthia

Dear Cynthia,
There are several issues that can cause freezing and excess condensation in AC units. The first thing I would look at is the evaporator coil. As covered earlier in air conditioning Q&A’s, it’s important to understand how the air conditioner operates to track down the problem.

The fan motor turns the squirrel cage. That draws moist, warm inside air through the air return of your rig up into the unit. The air is drawn through the evaporator coil. It is similar to the radiator of your car and has coolant flashing through tubing inside. This pulls hot air into the tubing and removes moisture. This moisture falls to the drip pan and goes to weep or drain holes on both sides.

The air is cooled approximately 15 degrees and the squirrel cage pushes it back down into the rig.

You did not mention if you have ducted roof air or simple down-draft models; however, with a 5th wheel I would assume they are ducted.

Check the evaporator fins on the AC units

The next thing I would check is the evaporator fins on the AC units to ensure they were clear and allowing good air flow. Next, make sure the pan is clean and moisture is getting to the drains and they are not plugged as well.

Next, make sure all of your interior ceiling vents are open and have good air flow. I would take off the return air cover and take a look at the baffle and vents. Excess moisture blowing into the rig is caused by a buildup of moisture in the pan and not getting out.

What can cause freezing in the AC units

Freezing can be caused by poor air flow of the cool air building up in the ducting before getting to the vents. It can also be caused by exposed metal in the air conditioner and vents. Exposed metal gets cold and warm moist air coming through the return vent hits the cold metal and you get condensation.

Another issue is poor air circulation to the vents due to RV manufacturers not installing a baffle correctly. The air conditioner manufacturer makes their roof air models generic so the air comes down off the squirrel cage directly below. Models that do not have ducted roof air use this model with an interior shroud that has the controls and vents.

Sometimes baffles are installed incorrectly

Models that have ducted roof air purchase a baffle that is installed by the RV manufacturer that diverts air flow to the appropriate direction of the ducts and vents. This baffle needs to be cut to the appropriate length and installed with furnace ducting tape. Unfortunately, I have seen quite a few units that have this baffle cut too short and taped with a single piece of duct tape. That can allow too much air go to the wrong place. Or, worse, it falls out and blocks air flow and just recirculates into the return air and back. This could cause a buildup of cold air in places where it doesn’t get drawn back up and excess condensation results.

Check those items on your AC units. Also, try to get a little more air flow inside your rig and reduce moisture by cooking less of what causes steam, limit hot showers during hot/humid times, and don’t hang wet items like towels inside. Limiting inside moisture can help with this, as well.

Read more from Dave here

Dave Solberg worked at Winnebago for 15 years developing the dealer training program, as marketing manager, and conducting shows. As the owner of Passport Media Creations, Dave has developed several RV dealer training programs, the RV Safety Training program for The Recreation Vehicle Safety and Education Foundation, and the accredited RV Driving Safety program being conducted at rallies and shows around the country. Dave 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.


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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.


  1. Then cool air coming out of the air unit hits the hot metal and you get condensation.”

    That’s not worded correctly. Warm moist air hitting cold metal causes condensation.

  2. It’s all about air flow. Keep the filter clean. And it may be too late for that. Dirt may already have settled deep within the coil. They are 2 to 3 inches deep. If that’s the case, the unit may have to be removed and pressure washed. If you have a sturdy roof it can be done up there or it may have to be removed for cleaning. Ive done cleaning to hundreds of them. It may be a good time to put an ampmeter on it and see if the current is approximately right. A good way to see if the compressor is fully working. Unfortunately they don’t install ports in the refrigeration. ( it might cost $3). Also, check the drain pan like suggested. Or make sure the drain isn’t plugged. Ive seen that a lot because of the mold, especially in the southern states.

  3. The dripping on the bed sounds very familiar, after 3 visits to the local dealer and over $100 in labor fees my son in law and I found a crack in the drip pan allowing water to drip out of the discharge ceiling duct directly over the corner of the bed where my feet were. Using waterproof epoxy we covered the area where the crack was and wouldn’t you know it the leak stopped. I no longer waste my time or money at the local dealer. Good luck, get a bright flashlight and paper towels to clean the drip pan good, wipe the crack good with rubbing alcohol before applying epoxy.


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