How Do Propane (Gas Absorption) RV Refrigerators Work?

Posted by Brian Currier on 29th Sep 2025

How Do Propane (Gas Absorption) RV Refrigerators Work?

Off-grid, you don't always have shore power. That's where propane RV refrigerators, also called gas absorption refrigerators, earn their keep: they keep food cold for days on a tank of LP, with no compressor and almost no moving parts. Knowing how they work is the best way to keep yours running like new.

The short answer

An absorption fridge uses heat (a propane flame or an electric heating element) to boil ammonia out of a water solution. The ammonia condenses outside the fridge, then evaporates in the cooling fins inside it, which makes those fins very cold. The cold fins chill the freezer and fridge. Heat in, cold out.

The four key players

A household fridge uses a compressor to pump refrigerant around. An absorption fridge replaces that compressor with a heat-driven chemical loop built from four ingredients:

NH3
Ammonia
The refrigerant. It does the actual cooling when it evaporates.
H2O
Water
Soaks up ammonia gas, then gives it back up when heated.
H2
Hydrogen
Lowers the ammonia's partial pressure so it can evaporate at cold temperatures.
HEAT
Heat source
A propane (LP) flame or a 120V/12V electric heating element.

The cooling cycle, step by step

Everything is sealed inside the cooling unit, the maze of tubes on the back of your fridge. Follow the numbers:

How a gas absorption RV refrigerator cooling unit works Heat at the boiler drives ammonia vapor up to a separator, through the condenser outside the fridge where it turns to liquid, into the evaporator inside the fridge where it evaporates into hydrogen and makes the cooling fins very cold, then into the absorber where water reabsorbs it and returns to the boiler. INSIDE THE FRIDGE BEHIND THE FRIDGE (OUTSIDE VENT) vapor rises SEPARATOR RESERVOIR BOILER LP flame or electric element EVAPORATOR ammonia evaporates into hydrogen & gets very cold cold fins chill the box CONDENSER vapor sheds heat outside & turns back to liquid ABSORBER water soaks the ammonia back up; cycle repeats 1 2 3 4 5 Ammonia vapor Liquid ammonia Ammonia + hydrogen Ammonia-water solution
Simplified cooling-unit diagram. Real units add a rectifier, hydrogen return and weak-solution line, but the loop is the same.
1
Heat the solution. A small propane flame (or the electric heating element) heats an ammonia-water mix in the boiler.
2
Separate. Heat boils ammonia vapor out of the water. The vapor rises to the separator; the water drains away.
3
Condense. Hot ammonia vapor flows through the finned condenser, dumps its heat out the vents, and turns back into a liquid.
4
Evaporate (this is where the cold happens). In the evaporator inside the freezer and fridge, liquid ammonia meets hydrogen gas and evaporates at a very low temperature. That makes the cooling fins and plates ice-cold, and they chill everything in the box.
5
Absorb. The ammonia gas is absorbed back into the water in the absorber, flows back to the boiler, and the loop repeats for as long as heat is applied.
Heat in → cooling out. No compressor, no pump, just physics.

Strengths & limitations

Why RVers love them

  • Boondocking friendly. Sips propane, so a tank lasts a long time.
  • Silent. No compressor buzzing or cycling at night.
  • Durable. With no moving parts in the cooling loop, they last for years when maintained.

What to watch out for

  • Must be level when parked (see below).
  • Slow to cool. Expect several hours to reach temp; start it the night before a trip.
  • Heat sensitive. High outside temps and poor ventilation cut performance.

⚠ Level matters more than anything else

The cooling unit relies on gravity to move liquid through its tubes. Run it too far off level while parked and the liquid stalls, the boiler overheats, and the unit can be permanently damaged. Off-level operation is the #1 cause of cooling-unit failure we see.

Rule of thumb: level the coach every time you set up camp, and check your owner's manual for your model's exact tolerance. If you're unsure whether yours is already damaged, check our RV fridge error code tool or browse Norcold and Dometic replacement cooling units.

Maintenance checklist

✓
Keep vents clear. Wasp nests, leaves and debris choke airflow. Check the outside vents.
✓
Check door seals. Close the door on a dollar bill; if it slides out easily, the seal is leaking cold air.
✓
Inspect burner & flue. Soot or rust on the burner and orifice causes weak flames and poor cooling on LP.
✓
Add vent fans. Norcold or Dometic cooling-unit fans make a big difference in hot weather.

Spare parts to keep on hand

A few inexpensive parts fail far more often than the rest. Keeping spares in the rig can save a trip (and a cooler full of food).

Norcold refrigerators →

Dometic refrigerators →

Final thoughts from the Fridge Guys

A propane RV fridge can feel like magic, but it's clever chemistry using heat to move heat. Keep it level, keep it ventilated, keep a few spares on board, and it'll keep your food safe wherever the road takes you.

Not sure which part fits?

Find genuine Norcold, Dometic, Furrion, InVision and GE parts by your fridge's model number.

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