AC Not Cooling

As the weather gets warmer, the RV air conditioner struggles to keep up. Is it working?

Here’s how to tell. Most RV air conditioners can expect a delta T of about 20 degrees. What is delta T? It’s the difference in temperature between the air going into the air conditioner, and the cooler air coming out. So if the air going in is 80 degrees, then air coming out will probably be around 60 degrees. (80 – 20 = 60).

Unfortunately our RV’s are not very well insulated. So a hot summer day can really tax an air conditioner. You can give your AC a head start by blocking light from coming in through the windows. Set your AC temperature low during the night and early morning hours so that when it gets warmer in the day, the RV will be cooler.

You can also make sure that your AC air filters are clean, and that the inside of the condensor and evaporator fins are kept clean. AC’s work best when there is good airflow. Dirt in these fins will block the flow of air, and reduce the efficiency of your AC.

I think my AC is low on Freon and needs to be recharged.

As an RV tech, I often get phone calls like this. Unfortunately it’s doesn’t work that way with RV air conditioners. First of all, RV air conditioners don’t use the normal refrigerant that is used in automobiles (R-134a). Most use R-410 and even that is being phased out for R-32.

RV AC manufacturers design their AC’s to not be refilled. It is a sealed system, meaning that there are no refill ports that can be used to evacuate and refill refrigerant. So if your refrigerant is low, it means that there is a leak in the system somewhere. So while it is possible that you could refill it and make it work again, it is not practical to do so.

Most of the time the leak is very small, like a pinhole leak. You have to find the leak, fix it, then test to see if all the leaks have been found. Most HVAC techs do this by drawing a hard vacuum, then seeing if the vacuum holds for an extended period. Even if one leak is fixed, it doesn’t mean that there is not another one.

Then you have to add filling ports. This could be done by brazing a new port, or worse yet, you could use a saddle valve which pierces the copper tube to make an opening. Unfortunately this just adds another possible leak into an appliance that sits on your roof and shakes as it goes down the road.

Any brazing or welding that needs to be done would need to be done on the roof of your RV outside.

A typical new RV AC will cost about $1500. Installation might be 2 to 3 hours, so add about $400 onto that. The time required to add refill ports, fix an RV AC leak, pressure test, and refill will be about 6 hours, spread over several days. R410 is going to cost about $50-$100 per pound. A typical RV AC holds about 2.5 lbs. Add all those costs up, and we’re at about $1350. The problem is that you never know if all of the leaks have been found. So after going through this process, the AC might work for a short time, only to stop working again. If that happens, you have to repeat the process again. More $$$. If you instead got a new AC, if it stops working, the warranty on the AC will cover replacing it.

What to see what’s involved in repairing and refilling an RV AC. Look at this video:

Not every AC issue involves low refrigerant. There can be other reasons why an AC won’t work. The only way to find out is to do some diagnostic tests. Some other possible areas could be:

1. Bad compressor or fan capacitors.
2. Bad or disconnected freeze sensor.
3. Burnt out thermal overload devices.
4. Defective thermostat.
5. A break in the thermostat wires … sometimes caused by rodents over the winter.
6. Bad fan motor.
7. Bad compressor relay in the control board.
8. Blown circuit breaker, or no power to the thermostat. Sometimes the thermostat gets it’s power through the furnace. So if the power switch on the furnace has been turned off, it will not get power.
9. Dirty fins, coils, or air flow obstructions.

All of these issues can be repaired. The ones that cannot involve a break or leak in the sealed refrigerant system, which also includes the compressor itself. You can’t replace the compressor without breaking the sealed system.

Think your RV AC is not cooling? Get two thermometers, put one in the air going in, and another in the air coming out. Measure the difference. Is it 20 or more? If so, it’s doing as expected. If not, then it’s time to start diagnostic tests to determine why.