RV Air Conditioner Maintenance Tips

A few months back I went to turn on the trailers AC unit, and it made a funny sound. It was muted compared to normal, and no air was blowing out the vents. I headed up on the roof for a look see. After removing the plastic cover, I had Anne turn on the AC again. Right away I noticed the fan motor wasn’t turning.

I had her shut it down, and I tried to move the fan. It moved, but I found it took a little effort to get it going. I spun it a few times back and forth with my hand, and things seemed to free up. We fired up the AC once again and off it went spinning normally. I tried it on and off during our winter trip south, and it worked fine.

Coleman Mach 3 air conditioner –  Model AirXcel 48203A866

Disclaimer: Iā€™m not a certified RV technician merely an RV owner. This post and video should not be taken as instructional. If you decide to do the things depicted in the video, do the research and be aware of all risks involved. I accept no liability, you have been warned. ā€“ Ray

Corrosion Seizes the AC Fan Shaft

I believe the cause was a little bit of corrosion that had formed on the motor shaft during the few months in the fall where we didn’t use the AC. We spend the fall season on the west coast close to the ocean, so things tend to rust. Once broken free it worked fine again. While I had the AC apart troubleshooting the stuck fan, I noticed that the evaporator coil was extremely dirty.

Dirty Evaporator coil

In 7 years I have never even checked it. Doh! Next time I had the chance I promised myself I would pull the air conditioner all apart and give it a good cleaning and check over. Now as we head into summer and will need the AC often, it’s a good time to perform the task. I hit up Amazon and ordered up some products and tools for the job.

Cleaning the Coils

First I TURNED OFF ALL POWER to the air conditioner by unhooking the AC power cable and disconnecting the 12-volt batteries. I started with the evaporator coil removing the sheet metal covers. They were held in place by short Philips head screws. (Tip: wear work gloves to avoid getting cut by the sharp metal edges)

Next, I unplugged the green control board Molex connector and pulled out the freeze sensor probe from the coil. I then tucked the electronic control module into the air return venting inside the RV. 

AC unit with the covers removed

To keep coil cleaner, rinse water and debris from entering the RV I used a kitchen garbage bag to block the opening. I also protected the squirrel cage blower fan opening with one of the metal covers. I soaked the evaporator coil really well with the foaming cleaner and let sit for 10 minutes. 

Evaporator coil foamed up

Then using a Bullseye nozzle dialed into a fine spray, I carefully rinsed the fins, taking care not damage any of the fragile aluminum fins. Since my evaporator was so jammed up with gunk, it needed several clean and rinsing cycles. I ended up using the whole can but finally got her done.

Hosing off the coil and fins with the Bullseye spray nozzle

Next, I made sure to thoroughly rinse out the plastic pan below the evaporator coils and clear the drain holes. The pan is used to catch and drain condensation that develops on the fins during normal operation. I reconnected the wiring and replaced the metal covers and moved on to the condenser coil.

My condenser coil wasn’t too dirty I guess because its exposed to the weather and we spend a lot of time in rainy conditions. I sprayed on the condenser cleaner and made sure to rinse it all off. From the warnings on the can it was much more caustic than the evaporator coil cleaner, so I also made sure to rinse off the rubber roof and trailer side walls afterward.

Cleaning condenser coil

Straightening Bent Coil Fins

With the proper tool, straightening bent fins on the condenser and evaporator coils was surprisingly easy. It just took a bit of patience. Of the two brands I tried, I liked the Supco over the Robinair but not by much. They both could do the job, just a personal preference. I found that the 16 blades per square inch comb worked the best.

Fin comb in use

AC Motor Shaft Lubrication

From what I could gather with research online and comments from my video viewers the motor I have doesn’t require oiling. The bearings are sealed and self-lubricating.  I did spray some silicone lubricant into the shaft opening at the end of the motor where some rust had built up. I believe that’s what caused the motor shaft to stick. The silicone spray removed the rust for the most part and should help protect it.

Lubing motor shaft

RV air conditioner enclosures are notorious homes for critters like wasps. With a flashlight, I took a look at every nook and cranny. Luckily mine was not a home for them.  Finally, I did a visual inspection of the compressor, capacitors, and wiring before putting the outside plastic cover back on.

Outside AC maintenance completed

RV AC Maintenance Inside the Rig

Once the rooftop part of the AC maintenance was done, it was now time to do a few things inside. I removed four screws holding the cover and vacuumed out the vents. I visually inspected the squirrel cage fan looking for excessive dust and debris.  It looked pretty good so no need to disassemble to clean. A blow out with compressed air would be sufficient.

Inside AC unit squirrel cage view

Next, I removed old foil duct tape that was starting to peel off and replaced with fresh strips. The better the seals in here, the more cooled air will be channeled into the rig and not escape into the attic area. I had a look at the wood and insulation in the attic area surrounding the AC unit checking for any signs of water leaks.

Any leaks would indicate a faulty rubber gasket or insufficient torque on the mounting bolts. so, I checked tightness the four mounting bolts that hold the outer and inner parts of the AC in place. All was good. To finish off the inside maintenance, I removed the OEM foam AC filter and washed it with warm water.

Testing the RV AC Operation

To complete my job, I reconnected AC and DC power to the air conditioner and turned it on. I checked high and low-speed fan operations. The fan sounded smooth, and the vents had good air flow. I let it run for 15-20 minutes then using my infrared temperature gun I compared input and output air temperatures. 

Checking output temp

I measured an ambient rig temperature of 75F and an AC output temp of 50F. 25 degrees is considered a good differential according to the Coleman Mach 3 user manual.

Video Detailing My RV AC Maintenance

I feel much better now that the air conditioner is back in tip-top condition and ready for our summer RV adventures.

Parts List:

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