# Yellow Powder Behind the Fridge Means the Cooling Unit Is Done

> Yellow or green powder in the rear refrigerator compartment is sodium chromate, the corrosion inhibitor in an absorption cooling unit charge. Its presence means the sealed system has leaked ammonia and the cooling unit is unrecoverable. The options are a replacement cooling unit, a new refrigerator, or a residential conversion.

**Type:** Journal article  
**Canonical:** https://ocrv.pro/journal/yellow-powder-behind-an-rv-refrigerator  
**Updated:** 2026-07-29

## Summary

Yellow residue on the boiler tube is sodium chromate escaping with ammonia. The sealed cooling unit has failed and cannot be repaired in place. It is replace or convert.

An absorption refrigerator has no compressor. It moves heat using a sealed charge of ammonia, water, hydrogen and sodium chromate, circulated by heat applied at the boiler rather than by a pump. There are no moving parts in the cooling loop at all. It is an elegant design and it has one absolute failure mode: if the sealed charge escapes, the unit is finished, permanently, and nothing can be done to the loop itself.

The tell is a yellow to greenish powder deposited on the boiler tube or on the insulation around it, visible through the exterior access panel on the side of the coach. That powder is sodium chromate, which was in solution inside the tubing as a corrosion inhibitor. When ammonia solution escapes and the water evaporates, the chromate is left behind as a stain. There is no other source for it.

Owners often find this while chasing a different complaint, usually the fridge not holding temperature on propane. Here is what the finding actually means, what caused it, and what the realistic paths forward look like.

## What Actually Causes the Loop to Let Go

Two mechanisms account for most failures. The first is internal corrosion at the boiler, where the highest temperatures occur. Over years, thermal cycling and any degradation of the chromate inhibitor allow the tube wall to thin from inside until it perforates. This is age related and it is why cooling units have a practical service life rather than an indefinite one.

The second is crystallization from operating out of level. The absorption cycle relies on gravity flow of the solution through the loop. Run a fridge for extended periods on a coach parked significantly off level and solution pools in the wrong place, sodium chromate precipitates out and forms a solid blockage. That blockage causes a local overheat at the boiler, and the overheat produces a rupture.

The out of level scenario is worth taking seriously because it happens on a timescale of hours, not years. A weekend spent parked on a driveway slope with the fridge running is a real risk. On the road it matters less, because the coach is moving and the solution keeps circulating. Parked and off level with the burner cycling is the dangerous combination.

- **Boiler tube corrosion:** Age driven thinning at the highest temperature point in the loop. The dominant failure mode on units past roughly twelve to fifteen years.
- **Chromate crystallization:** Operating significantly off level lets solution pool and the inhibitor precipitate, forming a blockage that causes a localized overheat.
- **Burner overfire:** A dirty burner or an obstructed flue running rich concentrates heat on one area of the boiler and accelerates tube failure.
- **Flue blockage:** Insect nesting in the flue is common in coaches stored outdoors and produces exactly the overheat condition that kills a boiler.

## Confirming It Before Spending Money

The powder is close to conclusive on its own, but confirm with two other observations. First, smell. Ammonia has a sharp unmistakable odor and it lingers in the rear compartment for a long time after a leak. If you open the access panel and your eyes water, that settles it.

Second, behavior. A failed cooling unit typically cools poorly or not at all on both propane and electric, because the fault is in the loop rather than in either heat source. If the unit cools fine on electric and not on propane, that is a burner, flue or gas supply issue and the cooling unit is probably fine. That distinction saves a lot of unnecessary expense.

Third, check for a gurgling that never settles. A healthy absorption unit is essentially silent once it stabilizes. Continuous gurgling or a sloshing sound long after startup suggests the loop is not circulating properly, which can precede a full failure and is worth investigating before the powder appears.

## Replacement Cooling Unit, New Fridge, or Residential Conversion

A replacement cooling unit is the cheapest path in parts terms. The refrigerator box, doors, controls and trim all stay. The sealed loop assembly is unbolted from the back of the box and a new or remanufactured unit takes its place. This is a solid option on a coach where the cabinet opening is an unusual size, which is common on older coaches where a modern unit will not fit the hole.

A complete new absorption refrigerator makes sense when the box itself is tired: door seals gone, hinges worn, controls failing, interior shelving broken. You are replacing the whole appliance rather than the one component that failed. Fit is the constraint, since cabinet openings are model specific and the aperture may need modification.

Residential conversion is increasingly what owners choose. A 120 volt compressor refrigerator, powered by an inverter and an adequate battery bank, cools better, is unaffected by level, and costs less to buy than a comparable absorption unit. The catch is the power system. A residential fridge draws real energy overnight, and doing this properly usually means a battery and inverter upgrade at the same time, which is where the budget grows.

- **Cooling unit replacement:** Keeps the existing box, doors and controls. Best where the cabinet aperture is nonstandard and modern units will not fit.
- **New absorption unit:** Appropriate when seals, hinges and controls are also failing. Cabinet opening modification is frequently part of the job.
- **Residential conversion:** Better cooling and level insensitivity, but requires inverter and battery capacity. Plan the power system as part of the same project.
- **Twelve volt compressor units:** A middle path with lower power draw than a residential unit and no inverter dependency, though the sizes available are limited.
- **Cabinet and venting rework:** Any change of refrigerator type changes the venting requirement. Roof vents and lower intakes may be sealed or reworked accordingly.

## The Power Math Behind a Residential Conversion

This is where conversions go wrong. A typical residential refrigerator in an RV draws somewhere in the range of 1.0 to 1.5 kilowatt hours per day depending on size, ambient temperature and how often the door opens. Against a 12 volt battery bank, that is roughly 85 to 125 amp hours per day at the battery.

A pair of group 27 lead acid batteries gives you maybe 100 usable amp hours before you are damaging them. That is not one day of refrigerator operation with anything left for lights and the water pump. So the honest version of a residential conversion, for anyone who boondocks or dry camps at all, includes a lithium bank and enough solar to replace what the fridge consumes.

Battery work runs $500 to $5,500, inverter work $750 to $4,500, and solar $1,500 to $12,000. A refrigerator at $400 to $4,500 is often the smallest line on the invoice. For an owner who is always on shore power, none of that applies and the conversion is simple. The conversation has to start with how you actually use the coach.

## Keeping the Next One Alive Longer

Level the coach before running the fridge while parked. Not perfect, but within the manufacturer tolerance, which is usually a few degrees. Leveling system work runs $350 to $6,500 and a functioning leveling system pays for itself in refrigerator life alone on a coach that spends time on sloped storage or driveways.

Clean the burner and inspect the flue annually. Insect nesting in flue tubes is common on coaches stored outdoors in this area, and it is the leading preventable cause of boiler overheat. It takes twenty minutes and it is the highest value item on an absorption refrigerator service list.

Improve rear compartment airflow. Absorption units reject heat by convection through the sidewall vents, and a compartment that runs hot works the boiler harder. Making sure the upper vent is clear, the baffle is intact, and there is no accumulated debris in the compartment measurably lowers operating temperature. On coaches parked with the fridge side facing afternoon sun through a long southern California summer, an auxiliary vent fan is a reasonable addition.

## What is included

- Yellow or green powder is sodium chromate and has only one source
- A leaked absorption loop cannot be repaired in place, ever
- Boiler corrosion and off level crystallization cause most failures
- Poor cooling on propane only points to the burner, not the cooling unit
- Three paths exist: cooling unit, whole appliance, or residential conversion
- Residential conversions are a power system project, not an appliance swap
- Flue inspection annually is the highest value preventive item
- Leveling before running the fridge while parked genuinely extends its life

## Questions

### Is the yellow powder behind my RV fridge dangerous?

The residue itself is a chromate salt and should not be handled without gloves, but the more immediate concern is the ammonia that escaped with it. Ventilate the compartment, do not run the unit further, and avoid breathing in the enclosed space. Once the leak has occurred the charge is gone, so the ongoing hazard is limited, but the appliance should be taken out of service.

### Can a leaking absorption cooling unit be recharged?

No. The loop is a welded sealed assembly with no service ports, and the charge includes ammonia under pressure along with hydrogen and a chromate inhibitor. Once it has perforated, the tube has failed and even a successful recharge would leak again through the same defect. The cooling unit assembly gets replaced or the whole refrigerator does.

### Should I convert to a residential refrigerator?

It depends entirely on how you use the coach. On shore power most of the time, a residential unit cools better, is insensitive to level, and often costs less than a comparable absorption unit. If you dry camp, the fridge consumes roughly 85 to 125 amp hours per day at 12 volts, which realistically requires a lithium bank and solar. Plan the power system first.

### My fridge works on shore power but not propane. Is the cooling unit bad?

Probably not. A failed cooling unit performs poorly on both heat sources, because the fault is in the sealed loop rather than in either burner or heating element. Cooling well on electric and poorly on propane points to the gas side: a dirty burner orifice, an obstructed flue, weak propane pressure, or a thermocouple issue. That is a much smaller repair.

## Related

- https://ocrv.pro/repairs/appliance-service
- https://ocrv.pro/repairs/electrical-systems
- https://ocrv.pro/repairs/solar-and-power-systems
- https://ocrv.pro/rv-service
- https://ocrv.pro/repairs/leveling-and-suspension