Refrigerator
A guided diagnosis for RV techs. Each step is a check, a reading or a question.
- Which fridge is in the coach? Read the label inside the fridge or on the data plate.
- What is the absorption complaint? Pick what the customer sees.
- What is the compressor fridge complaint? Pick what the customer sees.
- Residential fridge checks A residential fridge on an inverter needs 120V from shore, generator, or inverter, and a working inverter.
- Is the fridge level? An absorption fridge must sit close to level to circulate its coolant. Parked off level for a drive is fine; parked off level overnight is not. Expect: Level within about 3 degrees side to side and front to back
- Is there 120v at the fridge outlet? Meter the outlet in the fridge compartment and the heating element feed. Expect: About 108 to 132 V AC
- Does the gas burner light? Set it to gas and watch the burner at the back. Expect: Click, spark, then a steady blue flame
- How long has it been running? An absorption fridge takes hours to pull down. Ask when it was started and how full it is.
- Which fridge is showing it? Pick the brand on the eyebrow panel.
- Is the compressor running? Listen at the fridge. A compressor fridge should hum within a minute of power-up. Expect: A steady hum, about 1 to 5 A draw
- Check the condenser airflow Compressor fridges cool through the condenser. Check the vents and the condenser fan if fitted. Expect: Clear vents, fan runs if fitted
- Measure the draw Clamp the 12V feed. A typical 10 cf compressor fridge draws about 4 to 6 A running, more on startup. Expect: About 4 to 6 A running
- Read the controller led Compressor fridges use a Danfoss/Secop-style controller. A flashing LED names the fault.
- Is the inverter feeding the fridge? Meter 120V at the fridge outlet with shore off and the inverter on. Expect: About 108 to 132 V AC
- Feel the cooling unit At the back, the boiler area should be warm and the absorber coils warm. Use the back of your hand or an IR thermometer, not a firm grip. Expect: Boiler warm, coils warm top to bottom
- Where is the 120v lost? Check the breaker, the outlet, and the fridge plug.
- Check the heating element Power OFF. Meter the element for resistance: R = V squared / W. A 325W element at 120V reads about 44 ohm. Then power ON and meter 120V at the element. Expect: About 44 ohm for 325W. 108 to 132 V AC when on.
- 12v at the gas valve while it sparks? Back-probe the gas solenoid while the board is in trial for ignition.
- Find where the spark stops No click and no spark in gas mode.
- Where does the flame go? Watch the burner through the window while it lights.
- Check the easy things first Burner runs, box stays warm.
- Compressor runs, box stays warm Check airflow and the box first.
- Is there 12v at the fridge? Meter the 12V feed at the fridge connector. Expect: About 12.0 V or more
- Which mode is failing? Boiler is cold. Try each mode and watch.
- Code no co: no cooling detected No cooling detected. Expect: Do this first: The fridge is on but not getting cold. Check level, vents, heat source (LP and 120V), then run the full-run test. A cooling unit that failed gives this code.
- Code no fl: burner did not ignite or re-ignite Burner did not ignite or re-ignite. Expect: Do this first: LP valve open, tank has gas, burner tube clean, electrode gap and spark, 12V good, regulator pressure. Check for a blocked flue.
- Code no ac: no 120v ac available No 120V AC available. Expect: Do this first: Check the shore or inverter, breaker, GFCI, cord, and the 120V plug at the fridge.
- Code ac lo: 120v is too low 120V is too low. Expect: Do this first: Measure at the fridge under load. Fix the supply: pedestal, long cord, inverter or loose connection.
- Code dc lo: 12v control voltage too low 12V control voltage too low. Expect: Do this first: Charge or replace the battery. Check voltage drop on the supply wire and ground. Needs about 10.5 V or more.
- Code dr: door open more than 2 minutes Door open more than 2 minutes. Expect: Do this first: Close the door. Check the door switch and the latch.
Causes and repairs
Residential: doors or condenser
A residential fridge that cools poorly usually has door seal gaps or a dusty condenser.
Tools: hand tools
Check the door seals with a dollar bill test. Vacuum the condenser coils. Check the door switch.
Inverter draw too high
A residential fridge on an inverter can draw 60 to 150 A at 12V on startup. The battery bank and inverter rating must match the load.
Tools: clamp meter
Compare the fridge label amps with the inverter rating and the battery bank capacity.
Level the coach first
The fridge was off level, so the coolant cannot circulate.
Tools: level
Level the coach, wait a few hours, and retest.
Give it time
An absorption fridge needs hours to pull down, and it cools slower when it is full or the door is opened a lot.
Tools: none
Leave it on the coldest setting, keep the door closed, and check again in a few hours.
Start device or low voltage
It tries to start then clicks off. Danfoss controllers protect below about 10.5 V. Check the supply under load, then the start device.
Tools: multimeter
Meter the voltage at the fridge during a start attempt. If it sags below 10.5 V, fix the supply first.
Condenser airflow blocked
Blocked vents or a dead fan make the compressor run hot and cool poorly.
Tools: hand tools
Clear the vents. Test or replace the condenser fan. Retest.
Thermostat or charge
Airflow is good but the box stays warm. Suspect the thermostat/thermistor, or a low charge on the cooling circuit.
Tools: multimeter
Pull the thermostat sensor plug at the controller and ohm it. Open (OL) or 0 ohms means it's bad. Put it in ice water for 10 minutes and ohm again: the reading should change a lot from room temperature. If it doesn't, replace the sensor.
Fridge draw is normal
The draw is in range. The battery bank may just be too small for the usage pattern.
Tools: none
Compare the bank capacity with the daily draw. Suggest more battery or solar for off-grid use.
High draw or low voltage
High draw with low voltage points to a supply problem or a failing compressor.
Tools: multimeter, clamp meter
Meter the voltage at the fridge under load. Low voltage makes the compressor draw more and run hot.
Residential fridge fault
The inverter feeds it fine, so the fridge itself has a fault.
Tools: multimeter
Residential fridges: pull the start relay off the compressor. If it rattles or reads open across its terminals, replace it. Listen: a compressor that hums and clicks off every few minutes is the start device or compressor. Evaporator iced solid behind the freezer panel is a defrost failure: check the defrost heater for continuity and the defrost thermostat closed when cold, then the timer or board. Many residential boards also have a test mode on the control panel.
Cooling unit weak
The boiler is warm and the coils are warm, but the box is still warm. Suspect a weak cooling unit, a bad door seal, or a blocked vent.
Tools: IR thermometer
Check the door seals and the roof vent and baffle. If the coils are only warm at the bottom, the cooling unit is failing.
Breaker trips
A tripped breaker points to a shorted element or a wiring fault.
Tools: multimeter
Power off. Meter the element to ground for a short. Inspect the wiring for burns.
Outlet or cord
The outlet or the cord is dead.
Tools: multimeter
Meter the outlet. Check the plug for heat or a melted face. Replace the failed part.
Element failed
The element reads open, so electric mode cannot heat.
Tools: multimeter
Replace the element with the same wattage and voltage. Retest.
Board or control
Power and element are good, so the board is not turning the element on.
Tools: multimeter
Check the mode switch and the board output to the element. Replace the failed control.
12v feed problem
The fridge has no 12V. On absorption fridges 12V runs the board even in gas mode.
Tools: multimeter
Check the fridge fuse and the feed. Fix the open.
Controller or compressor failed
12V is present but the compressor never runs. Suspect the controller (Danfoss/Secop) or the compressor itself.
Tools: multimeter
Danfoss/Secop BD controllers: check the LED blink code first. Then jumper the thermostat terminals (C to T) on the controller: if the compressor starts, the thermostat is bad. If it doesn't start and there's no blink code with good 12V at the controller, replace the controller.
Cleared
Cleared. Run it through a full cycle twice before you sign it off.
Write down what you did and the reading that proved it.
Board not opening the gas valve
The igniter sparks but the valve never gets 12V.
Tools: Multimeter
Meter the board's 12V input during the try: under about 10.5 V and the board won't run the valve. Good input and nothing out to the valve: replace the board.
Blocked burner or orifice
Something is blocking the gas or the flame path.
Tools: Flue brush, alcohol, compressed air
Clean the burner tube with a brush. Soak the orifice in alcohol and blow it out (never a pin or wire). Reinstall the burner centered under the flue, and clean the flue with a flue brush while you're there.
Low gas pressure or valve
The valve has 12V and the burner is clean.
Tools: Multimeter, manometer
Ohm the gas valve coil: open means replace the valve. Coil OK: have a qualified tech check pressure at the fridge with it trying to light (about 11 in WC).
Igniter wire
The spark has no path.
Tools: Hand tools
Replace the high-voltage wire or push it on firmly at both ends. Retest.
Electrode
The electrode can't throw a spark to the burner.
Tools: Hand tools
Replace the electrode and set its tip over the burner slots at the same spacing as the original.
Igniter or board
Wire and electrode are good, but there's no spark.
Tools: Multimeter
Meter 12V into the igniter (separate module) or the board in gas mode. 12V in and no spark: replace the igniter or board. No 12V: check the fridge fuse and the 12V feed.
Flame sense
The flame is good but the board doesn't see it.
Tools: Fine abrasive pad, multimeter
Clean the sensing electrode or thermocouple tip with a fine abrasive pad and make sure it sits in the flame. Thermocouple models: meter its millivolts as it lights; it should climb and hold. Stays low with a good flame: replace it.
Vent or wind
Draft is blowing the flame out.
Check the lower vent and roof vent caps are on and clear. Check the baffle is in the flue. Turn the coach or block direct wind while camping.
Vent or baffle
Heat can't leave the back of the fridge, so it can't cool.
Clear the roof vent, put the flue baffle back, and keep the back compartment clear. Retest after a few hours.
Door seal leaking
Cold air is leaking out.
Close the door on a dollar bill all the way around; anywhere it slides out easily leaks. Warm a flattened seal with a hair dryer to reshape it, or replace it.
Low charge or sealed system
Good airflow, good seals, compressor runs, no cooling.
Feel the evaporator: cold only near the inlet and warm after that points to a low charge. Hermetic units are usually replaced, not recharged.
Board has no 12v or isn't calling
On absorption fridges 12V runs the board in every mode. No board, no heat.
Tools: Multimeter
Meter 12V at the board under load: under about 10.5 V it won't run. Check the fridge fuse and the 12V feed. Good 12V and no output to the element or gas valve: replace the board.
Keep going on refrigerators
Learn it
- Absorption fridges (gas/electric)
- 12V compressor and residential fridges
- Absorption fridge won't run on gas
- Absorption fridge won't run on electric
- Is it the cooling unit?
Prove it
- Fridge won't run on gas
- Fridge is warm after unplugging
- Fridge works on gas, not electric
- Fridge won't cool on anything
- Freezer's fine, fridge is warm