One of the handiest, and most frustrating, of RV appliances has to be the refrigerator.

Just when you think everything is ready to go, you discover the %#@*&! thing isn't cool.

First off, you have to remember the unit doesn't operate like the refrigerator in your house. It's a gas-absorption unit which operates on the principle that when certain chemicals combine, heat is given off and when others combine, heat is absorbed.

That's how the system works, the combination of the right chemicals at the right time.

Most RV fridges work with distilled water, hydrogen and ammonia. When ammonia is mixed with hydrogen, heat is absorbed to provide cooling; when ammonia mixes with water, heat is given off.

To do all this requires heat and that comes from a gas flame or electric heat element.

The system has a generator and pump tube that works something like a coffee perk. A solution of water and ammonia is heated, boiling the ammonia out of the solution and carrying the mixture up the pump tube.

The ammonia gas rises up into the refrigerator where it mixes with the hydrogen gas, absorbing the heat and cooling the refrigerator.

The ammonia-hydrogen then follows the circuit back out of the refrigerator and down to meet the water, which is flowing back to the generator.

That's what all those tubes are in the back of the unit. Water likes ammonia more than hydrogen, so the ammonia is absorbed, giving off heat, and the hydrogen released.

And the circuit starts all over again, giving off heat.

Simple. So what goes wrong?

Well, ventilation is one of the keys. Heat must be easily given off so the solutions can flow freely and have enough heat to boil the ammonia out of the solution to create the pumping action.

Things to look for include a blocked or malfunctioning gas burner or bad electric element.

Bad ventilation will cut down cooling in every mode, so will a bad door gasket.

If cooling is non-existent, the cooling unit may have failed or you may have simply parked too far off-level. New units are less sensitive to level than older fridges, but you still have to be reasonably close.

Before you cancel your trip, there are some things you can check before you call the repair guy.

• First thing is to check that your unit is reasonably level.
• Then, if you've been running on household current, is the plug securely seated?
• If you've been running on propane, make sure you haven't run out. Battery power on a three-way fridge is seldom enough to provide initial cool-down, but should maintain cooling.
• If that all checks out, make sure the refrigerator isn't jammed with food to the point that interior air circulation is hampered, then be sure nothing's fallen in the ventilation area behind the fridge.
• Something you should have done when you put the unit into operation earlier this year is check the door seals. It's easy, just close the door on a sheet of writing paper and pull on it. If it slides out easily, the seal's too loose.