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Welcome back to another Two-Minute Tech Tip Tuesday, brought to you by the National RV Training Academy (NRVTA) – the largest hands-on RV training academy in America! Whether you’re here to solve an issue or simply sharpen your RV knowledge, don’t forget to subscribe so you never miss a tip that could save your trip.
🧊 The Question: Why Does My A/C Freeze Up on Low?
This week’s question comes from JackM1dB – sounds like a sound guy (get it, dB – decibel? We see you, Jack). He owns a Dutchmen Kodiak with a Dometic 35,000 BTU air conditioner, and he’s running into an issue:
“Why can’t my air conditioner run on low without freezing up and shutting off? It works fine on high, but on low or automatic, it freezes.”
That’s a great question – and it’s one that many RV owners run into without even realizing what’s going on under the hood (or rather, in the ceiling).
💡 Understanding How Your RV A/C Works
First, let’s break down what’s happening.
Your A/C is designed to pull warm, moist air from inside your RV and pass it over cold evaporator coils. This process cools the air, and as warm air hits those cold coils, moisture condenses into water. Pretty standard.
But when you’re running the unit on low fan speed, there’s less airflow moving across those coils. That means the moisture doesn’t get pushed off fast enough… and what happens to water that sits on a cold surface?
👉 It freezes.
🌀 What Happens When the Coils Freeze?
When the coils freeze, your A/C can’t operate efficiently – so Dometic designed a safety feature into the system. Inside the A/C unit is a thermistor, a small sensor that monitors the temperature (or more accurately, resistance levels measured in ohms).
When that thermistor detects freezing conditions, the A/C automatically shuts off the compressor to prevent damage. The fan stays on, continuing to pull in warmer air from the RV and melt the frost off the coils. Once the thermistor reads a safe value again, the compressor kicks back on.
This cycle is totally normal, and it’s designed to protect your compressor and maintain efficiency.
🌡️ What About “AU” Mode?
Jack also mentioned the “AU” (Automatic) setting on the thermostat. This setting is designed to start the unit on high speed and gradually switch to low speed as the cabin gets closer to the target temperature.
It’s a smart feature for energy efficiency, but yes – that low speed can lead to the same freezing issue, especially in humid conditions or poor airflow.
🛠️ The Verdict
- ✅ Freezing on low is a normal behavior, especially with high humidity and low fan speed.
- ✅ Your Dometic A/C is doing exactly what it’s supposed to by cycling the compressor off.
- ✅ Running the unit on “AU” is safe and efficient – don’t worry about it damaging the compressor.
Our advice? Let the system do its thing. If you notice frequent freezing, it might be better to run the fan on high continuously or look into improving airflow around the A/C vents.
🧰 Final Tip
Whether you’re a weekend warrior or a full-time RVer, understanding how your air conditioning system works can make all the difference in keeping your cool – literally.
And remember, NRVTA is here to help you learn these systems inside and out. Whether you’re troubleshooting, upgrading, or thinking about becoming an RV technician, we’ve got your back.
Got more questions? Drop them in the comments – or even better, bring them to class.
Until next time – stay cool out there!
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