How to clean up after a compressor burnout

What a burnout actually does to the circuit

When motor windings overheat and break down, the insulation decomposes. That reaction produces acids, and refrigerant circulating through a hot failing motor carries those acids and the carbonised debris everywhere the refrigerant goes — condenser, expansion device, evaporator, every metre of pipe.

So the failed compressor is the symptom you can see, and the contaminated circuit is the problem you cannot. A new compressor fitted into an acidic system is subjected to the same attack that killed the first one, usually with a shorter life because it starts with contamination already present.

Two things make this worse on modern systems. POE oil holds moisture and dissolves contamination more readily than mineral oil, distributing it more thoroughly. And moisture already present from poor evacuation is often what started the acid formation in the first place. Evacuation and moisture.

Mild or severe? The assessment decides the job

Test the oil rather than guess. An acid test kit costs a fraction of a compressor, and the assessment determines whether this is an afternoon or two days.

The clean-up sequence

• Recover the charge properly. It is contaminated — it does not go back in, and it should not be vented
• Remove the failed compressor and drain and inspect its oil. That oil is the evidence
• Replace the filter-drier without exception, and fit a suction-line drier with access ports so pressure drop can be monitored
• Deal with the expansion device. A TXV or capillary carrying debris will not meter correctly; clean or replace
• Flush where contamination is severe, or replace the components that cannot be cleaned
• Fit the new compressor with the correct new oil, in the correct quantity
• Evacuate deeply, with nitrogen breaks. This step is not optional after a burnout
• Charge by weight with virgin refrigerant — and as a liquid if it is a blend
• Run, then test acid again after a period of operation. Change the suction-line drier if it shows excessive pressure drop, and re-test

That last step is the one that separates a repair that lasts from one that returns. The first clean-up removes the bulk; running the system releases more contamination from the pipework, which the suction-line drier then catches. Skipping the follow-up leaves it circulating.

Contamination that has nothing to do with the compressor

Not every acidic system started with a motor failure. Two other routes matter in this market.

Moisture ingress — from inadequate evacuation, open POE oil, or uncapped pipework left on site — produces acid without any electrical failure at all. The compressor then fails and gets blamed.

Counterfeit or contaminated refrigerant. Adulterated gas has been found containing R-40 (methyl chloride), which reacts with aluminium in a system to form trimethyl aluminium — a compound that ignites on contact with air. This is not a theoretical hazard; it has caused documented injuries and equipment destruction internationally. It is the strongest practical argument for buying sealed cylinders from a documented source rather than the cheapest available. Why fake refrigerant is dangerous and how to tell genuine from counterfeit.

If a system has suffered repeated unexplained compressor failures, the refrigerant's provenance is worth investigating alongside the mechanical causes.

Related: Evacuation and moisture · Why fake gas is dangerous · Why HFCs need POE · Leak detection