Cleaning Up a Refrigeration System After a Compressor Burnout

A burned-out compressor leaves acid, carbon and sludge behind in the system. Change only the compressor, and that contamination attacks the new motor's insulation, plugs the metering device and can cause a second burnout within weeks. A proper cleanup is a planned job that takes several visits. You decide how far the damage spread, clean what you can reach, and keep testing until the numbers prove the system is clean. This work involves recovery, brazing and charging, so it belongs to a certified technician or a trainee working under one.

What You Will Be Able to Do

• Explain what a burnout leaves in a system and why it spreads.
• Tell a mild burnout from a severe one.
• Handle contaminated refrigerant and oil safely and legally.
• Plan and carry out a cleanup using suction and liquid line driers.
• Use pressure drop and acid tests to decide when the job is finished.

What a Burnout Does

When the motor winding fails, it reaches very high temperatures. The oil and the winding insulation break down. The result is a mix of acids, carbon and sludge. Any moisture in the system makes the acid worse. Polyolester (POE) oil is especially prone to this, because it absorbs water and can react with it to form acid.

Refrigerant flow carries all of that through the system. Carbon collects at the metering device and the driers. Acid stays in the oil, so anywhere oil sits is a place acid can hide. That includes accumulators, oil separators, suction traps and receivers.

Warning: Burned oil is acidic and can injure your skin and eyes. Wear chemical-resistant gloves and goggles. Do not breathe the fumes from a burned compressor, and ventilate the area before you open the system.

Confirm It and Judge the Spread

First, prove the compressor burned. Electrical tests show a ground or a short, and the oil confirms it. Then decide how bad it is.

Use an acid test kit made for the oil in the system. Mineral, alkylbenzene and POE oils can need different kits. If the test shows no acid, an oversized liquid line drier may be enough. If it shows acid, plan the full procedure.

The cause matters too. A burnout is often the end of a chain: low voltage, a failed contactor, moisture, or overheating. Find the cause while you are here.

The Full Cleanup

Step 1: Recover and Remove

1. Lock out power and verify it is dead.
2. Recover the refrigerant into a cylinder marked for contaminated refrigerant. Do not mix it with clean recovered refrigerant.
3. Change the recovery machine's filter when you finish. Acid and carbon will otherwise go into the next job.
4. Remove the compressor and cap its openings. A warranty claim may need it sealed.
5. Send the refrigerant to an EPA-certified reclaimer. Handle waste oil according to your state and local rules.

Federal rules still apply. Contaminated refrigerant must be recovered, not vented.

Step 2: Clean What the Acid Reached

1. Inspect or replace the metering device. A TXV with a removable screen can be cleaned. A capillary tube usually has to be replaced.
2. Inspect solenoid valves, check valves and any other small passages.
3. Drain or replace anything that traps oil, including accumulators, oil separators and suction traps.
4. Replace all existing filter-driers.
5. On a severe burnout, cut into the suction line near the compressor and look at the inside of the pipe. Black sludge there means a long cleanup.

Step 3: Install the Cleanup Driers

1. Fit an oversized liquid line drier rated for acid removal.
2. Fit a suction line filter-drier right ahead of the compressor, with pressure taps on both sides. This drier catches acid and carbon before they reach the new motor.
3. Flow dry nitrogen through the lines during every braze, so you do not add copper oxide scale to a system you are trying to clean.
4. Install the new compressor with the correct oil.

Step 4: Test, Evacuate and Charge

1. Pressure test with dry nitrogen. Never use oxygen or compressed air.
2. Evacuate to the target level, usually 500 microns or lower, and do a decay test. Several shops evacuate three times on a burnout job, breaking the vacuum with dry nitrogen between pulls.
3. Weigh in a clean charge, using virgin or reclaimed refrigerant.

Step 5: Run It and Watch the Numbers

1. Start the system and run it for one to two hours.
2. Measure pressure drop across the suction drier with a gauge on each tap.
3. If the drop goes above the drier maker's limit, the drier is loading up with contaminants. Pump down or recover as needed, and replace both driers.
4. Take an oil sample and test it for acid. If it is still acidic after driers are changed, change the oil too.
5. Repeat until the drop stays under the limit.
6. After about 24 hours of running, check the pressure drop and acid again.

Step 6: Finish and Follow Up

1. When the drop and the acid test are both good, remove the suction drier, or replace it with a suction filter if the maker recommends it. A suction drier left in place can load up later and starve the compressor.
2. Replace the liquid line drier with a standard size if needed.
3. Check the oil again after about two weeks.
4. Record every reading, and tell the customer about the follow-up visit before you start the job.

Why Suction Pressure Drop Matters

Suction pressure is low, so a small loss has a large effect. A drop across the drier makes the compressor see a lower suction pressure than the coil, which cuts capacity and raises the compression ratio.

Worked example, R-404A from the maker's chart:

The same 2 psi costs twice as much on a freezer. That is why drier makers publish lower pressure drop limits for low-temperature systems than for air conditioning. Use the limit on the data sheet for the drier and the application.

Worked Example: A Freezer Cleanup

A 5-hp semi-hermetic compressor on an R-448A walk-in freezer burned out, and the oil is black and acidic. Say the drier data sheet sets a 2 psi limit for this job. Yours may differ.

The rising pressure drop at hour 2 was good news. It showed that the driers were catching contaminants before they reached the new motor. Stopping after the first run would have left acid in the system.

Traps to Avoid

• Skipping the suction drier on a severe burnout. A liquid line drier alone does not stop acid that travels with returning oil.
• Leaving a suction drier in place to save a visit. It can become a restriction and starve the compressor.
• Using an acid neutralizer without checking. Some compressor makers do not allow these additives, and using them can void the warranty. Check before you add one.
• Flushing with a solvent the maker does not approve. Residue can damage a new compressor. Venting a flush refrigerant is illegal.
• Ignoring the receiver or oil separator on a large system. Acid oil left in a separator goes right back to the compressor.
• Reusing recovered refrigerant from a burnout. It goes to a reclaimer, not back into the system.

On a heat pump, the accumulator and the reversing valve also trap contaminants. Treat both as part of the cleanup.

Common Mistakes

Check Your Understanding

The oil from a burned compressor tests clean, and the drier shows no carbon. Is a full cleanup needed? Probably not. An oversized liquid line drier may be enough. Test again later to confirm it.

During a cleanup, suction drier pressure drop has climbed well past the limit after an hour. Is the job failing? No. The drier is doing its job, so replace both driers and keep running and testing.

A customer asks why you are coming back in two weeks. What do you say? The oil must be tested after the system has run, because acid can hide in the oil and only shows up over time.

A burnout happened on a system with an oil separator. Why does the separator matter? It holds acidic oil that will return to the new compressor unless it is drained or replaced.

You finished the job and the suction drier reads a tiny drop. Do you leave it in as cheap insurance? No, unless the maker says it may stay. A suction drier can load up later and restrict the compressor.

Key Takeaways

• A burnout spreads acid and carbon through the system, and acid follows the oil.
• Judge severity with the oil, an acid test and a look at the liquid line and suction line.
• Keep contaminated refrigerant separate, and send it to a reclaimer.
• Use an oversized liquid line drier and a suction line drier, and judge them by pressure drop.
• Test the oil again at 24 hours and at about two weeks.
• Remove the suction drier when the numbers are clean, and fix what caused the burnout.