Air-conditioner not working? Here’s 5 possible causes.

ByMarty LedwichDecember 24, 2020
Air-conditioner not working? Here’s 5 possible causes.

Most caravans and motorhomes will have an air-conditioner mounted on the roof where it tends to be out of sight and out of mind, that is until it breaks down. Fortunately, most issues can be traced back to a lack of maintenance or incorrect operation. We show you 5 things you can check to get your rooftop air-conditioner working again this summer.

Our caravan was fitted with an Ibis AirCommand III rooftop air conditioner. For 5 years, it had operated without any issues at all. That was despite the fact we had done almost no maintenance to it during that time. Then, during an extended stay in Townsville, Queensland, we started to experience some problems. It wasn’t cooling down the van anywhere near like it used to. It also started leaking a steady stream of water through one of the lights in the ceiling. At the same time, an error code flashed on the LED display. We switched it off, bewildered as to what the problem was. For the next 20 minutes, we could hear what sounded like chunks of ice falling inside the unit. It was time to do some investigation into what was causing the problems.

After researching the issues on the internet and taking apart our air-conditioner, we found these five common problems and what to do to try to fix them.

Correct settings:

One thing our research revealed is that, like most owners who experience issues with their rooftop units, we had the thermostat set at too low a temperature. These air-conditioners are good but they can not perform miracles. If the outside temperature is above 35 degrees and the relative humidity is above 50%, the unit will struggle to get the internal air down to the set temperature. The compressor will run continuously trying to keep up. This builds more condensation on the radiator fins which can freeze into ice, further reducing the cooling effect. By setting the thermostat to a temperature between 23 and 25 degrees, the unit doesn’t need to work as hard and can cycle effectively maintaining the set temperature.

Internal Filters:

The next thing to check is to ensure the internal air filter(s) is not clogged up with dust. We already knew that this needed to be cleaned regularly but what we found out was, because we were running the air-conditioner all day, it required more frequent cleaning. Sometimes as often as once every couple of days. Cleaning the filter is not difficult but you need to ensure you do a thorough job. We used a blower tool to remove the bulk of the dust and then cleaned the rest off using a bucket of soapy water and a small brush capable of getting into the grooves of the filter. You need to be very careful cleaning these filters. Some are more fragile than others.

air conditioner service - internal dust filter clean

The internal dust filter on the AirCommand III requires very thorough cleaning on a regular basis.

External drain holes:

Once having ensured the internal filter was clean, the next task is to check the roof-mounted unit itself. This is not a job for anyone afraid of heights or not confident on a ladder. It involves removing the plastic screws around the lower portion of the unit and lifting off the cover to expose the inner workings. When I looked at ours, I was shocked at how filthy it was under that cover.

CAUTION: Ensure your caravan is disconnected from the 240v mains before cleaning the roof-top unit.

After blowing out all the loose leaf matter and other debris, you need to check the drain holes at the base of the unit. Now all air-conditioners will be slightly different but they should all have a drainage system of some sort and it is likely to be very basic. In the case of the AirCommand III, there are a series of holes around the outside of the base.  These are all isolated from each other by plastic mouldings. Over time, these holes get blocked with dust and eventually prevent the condensation from draining away. In my opinion, it’s a stupid design as all it takes is for one or two of these drains to block up and you have the potential for condensation to run onto the heat exchanger radiator fins icing up or leaking back into the roof space. Nearly two-thirds of ours were blocked up with hard caked fine dust. Fortunately, unblocking them is a simple task.  Using a small screwdriver, I loosened the dust and blew out all the dirt using a blower tool.

Air conditioner service - drain holes

The AirCommand III has these drain holes all around the base of the housing. They all need to be cleared of any dirt and dust.

Heat exchanger radiator fins:

When you removed the main cover from the rooftop unit, you will expose the external fan and heat exchanger radiator. Next to that should be a separate polystyrene cover over a second heat exchanger radiator and another fan. These radiators are made from very thin aluminium and the fins are placed very close to each other. After a while, dust builds upon these fins and eventually blocks the space between them, preventing the heat exchangers from doing their job and reducing the efficiency of the unit itself. In our case, both of these radiators had copious amounts of dust caked over the fins. Cleaning these requires a degree of care as it is very easy to damage these fins. You can use a gentle brush and a blower tool to remove as much of the dust as possible.

If you do damage the fins, you can purchase a special tool that looks and works like a comb. Effectively you use it to bend the fins back into their original shape. It can also be used to remove the dirt in between the fins.

In really bad cases, you can purchase air-conditioner cleaning kits that use a special chemical sprayed on the coils and washed away with a gentle hose.  I tried it on our unit and I didn’t find it all that effective. In fact, it seemed to create more mess than it cleaned up. I think if your radiator fins are that badly clogged up, its time to get them cleaned by a professional.

Air conditioner service - dust build up

You can see how 5 years of dust has built up and blocked the radiator fins. You can also see the moisture stains where ice has built up.

Low or no refrigerant gas:

If you’ve tried all of the above and your air conditioner is still not functioning properly, chances are the refrigerant gas has either partially or fully leaked out of the cooling system. This is not an easy fix and will require a professional air-conditioner service technician.

Here’s the tricky part. Air-conditioner service technicians are easy enough to find throughout Australia especially up north.  What was difficult to find was a service technician who was willing to work on an RV rooftop air-conditioner. I must have rung around 20 of them in the Townsville area and all but one said they didn’t touch these systems. I suspect you will get that reaction no matter what town you find yourself in.

The one guy who did come out explained to me, in cases where the gas has leaked, regassing these systems is very difficult. Firstly it involves finding the leak and repairing it. Then the remaining gas needs to be purged and new gas pumped in. Unlike a car air conditioner, these rooftop units seldom have a proper connection for the regas system. Instead, they tend to be sealed by the copper pipe being bent back onto itself. Very few technicians will attempt to regas these systems and those that do are unlikely to offer more than a 3-month guarantee.

In our case, this appeared to be the cause of our unit’s failure. The heat exchanger radiators had been subjected to constant vibration from the van travelling on the roads and, in our case, worsened by our extensive dirt road travels. We had no choice but to purchase a new air-conditioner.

air conditioner maintenance - heat exchanger

If your air conditioner looks like this, it’s probably a good idea to have it cleaned and serviced by a professional.

Regular Maintenance:

The moral of this tale is that you must have your rooftop air-conditioner checked, cleaned and maintained on a regular basis. I would recommend once every two years at the very least even if you don’t use it all that often. The dirt and dust will accumulate even with the van sitting in storage and it will eventually lead to more problems. If you travel off-road or you live in your caravan for extended periods, you may need to look at more frequent servicing. Trust me when I tell you it’s no fun being stuck in the tropics, in 38-degree heat and stifling humidity without a functioning air-conditioner.

Safe travels.

Need a new air conditioner? Dometic Ibis 4 rooftop air conditioner review