Wednesday, September 27, 2023


How well is your RV air conditioner working?

Steve Savage submitted this article to when he was a Master Certified RV Technician with Mobility RV Service.

One of the calls we often receive during hot weather focuses on complaints about air conditioners needing Freon (more correctly, refrigerant) or a concern the AC is not working as well as it should.

Here is a simple test you can do at home or in the campground to make your own assessment using nothing more than your kitchen thermometer – and possibly save a service call.

Set your unit to “cool” and let it run continuously for at least 20 minutes, then with your kitchen cooking thermometer do the following:

1. Take the air temperature at the return where the air goes back into the unit, normally the rectangular opening with the filter in the ceiling. Insert the probe and write down the temperature.

2. Go to the outlet farthest from the unit where the air comes out and again take a temperature reading and write it down.

3. Now subtract the lowest number from the highest number.

4. If the result is in the range of 18-25 degrees, that is as much as the air conditioner is capable of and there is nothing that can be done to increase the output. It is dropping the incoming air temperature on average 20 degrees – that’s it.

☀ Run your RV air conditioner with only a small portable generatorYes, it’s true!

If your air conditioner output falls within that range and you are still too warm, you either need an additional air conditioner or a bigger air conditioner. You will get a value lower in the range when humidity is high, as the air conditioner has to dump humidity before it can reduce air temperature. When humidity is lower, the air conditioner can expand more of its energy reducing the incoming air temperature.



  1. There are two types of heat that the A/C must deal with, latent and sensible. Latent is heat in the form of humidity. If you are in a humid environment you will not achieve these sensible temperature drops, but they are correct for low humidity. So, an A/C technician would need to use a wet-bulb thermometer to accurately check the temp drop across the evaporator coil, but one can take an educated guess at it.

    For example at 90% relative humidity expect between 9 to 12 degree drop; at 60% expect 12 to 17 degrees; for 20% expect 20 to 25.

    Keep in mind that the temp drop is based on the air temp within the camper, not outdoors. If in a hot climate you’ll need to get a ‘head start’ before the outdoor temps get up there. This is because the A/C can only expel a fixed amount of heat per hour. So, as the ‘load’ increases your cabin temp may too, even with unit operating.

    To extract humidity, reduce fan speed.

    Sorry for the detail, before retirement I taught refrigeration/comfort cooling.

  2. Give it (air conditioner) a rest
    its a machine. It has no feelings. It can’t get sore or tired. The only reason I would do that would be because condensate was freezing on the coils because of too low a temperature or too low of refrigerant

    • I don”t know about that … My aging Bounder (machine) runs way too hot (sore) and has had trouble accelerating like it did in the old days, probably because of a clogged air filter (tired) ..

  3. I am so SICK and TIRED of getting thumbs down on my Comments that are based on 20 years of RVing experience! That I am NOT making any further comments on RV Travel again. I am NOT gonna offer anymore tips or tricks to successful RVing.

    You all have a good day!

    I’m out of here!

    • The 15 to 20 degree reduction in temperature is an absolute reduction based on physics of the refrigeration cycle not the total reduction in temperature that can be achieved. If that were true, you’d never get your home cooler than 80 degrees when the external temp was 100 degrees. It’s a progressive process of temperature reduction. If you can’t get the temp reduced more than, say, 20 degrees, that’s a function of AC capacity, external temperature, and insulation, not the absolute capacity of the AC unit.

    • Although you are correct in that many consider the rooftop units disposable, they are certainly repairable. I have repaired and replaced components on many rooftop units. Slow leaks can be managed by a leak stop solution and freon topped off, compressors can be swapped, etc. Certainly electrical problems, capacitors, relays, etc can be repaired or replaced.

      • If you’ve paid a professional to repair your a/c you may have already found it would have been more cost effective to purchase a new one with a 2 year warranty .. (based on $120/hr local RV shop labor rate)

        • Thank you for being another voice of reason in the roof top a/c discussion. So many folks don’t understand the process behind the technology at work.

    • The readers are the ones that give you a thumbs up or thumbs down, not the editors of the Daily Tips. So far, you have 5 thumbs down …probably because you’re acting like a spoiled brat…”I’m going to take my ball and go home!” To each his/her own. Just remember it’s the readers of a particular article that don’t like, or do like, whatever answer you gave, not the editors.


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