Internal Coil Cleaning

June 4, 2007
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To clean the whole system, a flexible hose can be used to bypass components such as the drier, accumulator, receiver, expansion valve or capillary tube. This allows unrestricted flow and eliminates trapping of the chemical at any point in the system.

Whether it’s a compressor burnout or a refrigerant retrofit, operating system coils sometimes need to be cleaned.

When a compressor burns out, the system (and/or the condenser coil at the least) needs to be thoroughly cleaned before the new compressor is in place and the system is restarted. Failure to do this may result in the new compressor burning out.

Today’s service technicians have options, such as flushing a system with an interior coil-flushing product or conducting a series of filter changes.

Years ago, the solution was easy. After a compressor burnout, most service techs would clean the interior compressor coils by spraying R-11 directly into the interior of the condenser and evaporator coils. The refrigerant breaks down hardened carbon deposits created by the burnout. It’s then flushed out of the system with the contaminants. This procedure left the coils clean, residue-free, and ready for use.

The use of R-11 is no longer possible because it is too expensive and it cannot be vented. Other fast-drying alternatives may be banned from jobsites due to flammability, health, and environmental concerns.

Internal coil-flushing agents have been in the industry for the past 15 years. Some have been designed for specific applications such as automotive a/c systems. Others encompass a broader range of applications. Chemical flushing agents are available for use in almost any type of application, including cascade systems.

COIL-FLUSH METHOD

In the coil-flushing method, the circulation of the coil flush loosens and dissolves the hard carbon deposits created by heat generated during a compressor burnout. This circulating action also aids in dissolving mineral oil and capturing acid. When the coil flush is blown out of the system with dry nitrogen, elements such as acid, oil, and liquefied carbon are removed from the interior coil lines.

A coil flush can be used when converting a system from mineral oil to a POE. The chemicals in the better brands of coil flush are completely miscible with mineral, polyolester, alkylbenzene, and polyalkylene glycol (PAG) oils.

Depending on the chemical flush used, the first flushing eliminates approximately 96 percent of the oil and acid accumulation when properly done. A second flushing will leave the system virtually free of any residual mineral oil. This process can be done in less than two hours, depending on the size of the system and the type of circulating pump being used.

A good coil-flushing agent is compatible with any refrigerant or blend. One coil flush manufacturer suggests that even if a service technician leaves a small amount of the coil flush in the system (5 percent or less of what was originally introduced), no harm will occur to the compressor or any of the integral parts of the system.

There have been reports that oils used in the manufacture and assembly of condenser and evaporator coils may lead to capillary tube plugging in R-134a systems. The flushing of these coils at the point of manufacture rids the coils of excess cutting oil and production residues, thereby reducing the risk of possible cap tube plugging after the coils have been in use for some time.

Service technicians can use the coil-flush method to clean out refrigerant recovery cylinders. These cylinders can accumulate contaminated oil, carbon, and acid over a period of time. Even if you fill the tank with virgin refrigerant, coming into contact with the built-up contaminants inside the cylinder can contaminate it.

Consideration should be given to a coil-flushing agent that is environmentally friendly. This could be one that has a low volatile organic compound (VOC) level, is biodegradable, and is HCFC-free. Service companies must evaluate which coil-flushing agents will accomplish the task without compromising employee or customer health.

APPROACHING THE JOB

When cleaning a system after a burnout, the service technician has two alternatives: Sections of the system can be isolated and cleaned individually (condensing coil, evaporating coil, etc.) or the entire system can be cleaned.

To clean the whole system, use a flexible hose to bypass components such as the drier, accumulator, receiver, expansion valve, or capillary tube. This allows unrestricted flow and eliminates trapping the chemical at any point in the system.

To completely dissolve oil, carbon, and tar deposits, the coils must be completely filled with the flushing chemical. The flushing period should be no less than 20 minutes. Completely filling the coils with the flush will create a scrubbing action that breaks down and liquefies hardened carbon and tar. This scrubbing action is essential to completely clean the interior of the coils.

Because most chemical flushing agents are nonpressurized liquids, the technician must use a pumping device such as a motorized chemical/acid/oil pump to circulate this chemical throughout the system. Even a hand oil pump (up to 2 hp) can be used on small applications, such as domestic refrigerators, in order to move the flushing agent throughout the coils.

While most chemical pumps do an adequate job of moving the coil flush throughout the system, the materials that come into direct contact with the coil flush must be considered. Neoprene, santoprene, nitrile, and polypropylene have a limited compatibility with most coil-flushing agents. Swelling or deterioration may occur, which can cause the replacement of the impeller, diaphragm, O-rings, or valves. Pumps manufactured with Viton® or Teflon® appear to be the most resistant to the chemicals that make up most coil-flushing products.

Publication date: 06/04/2007

Sidebar: Using a Coil Flush for Refrigerant Retrofits

Here is a general guideline for using an internal coil cleaner when retrofitting a system from mineral oil to a POE.

1. Recover refrigerant from the system and drain all mineral oil. Measure the amount of oil removed as a guideline when refilling with POE oil. Note: Check the manufacturer’s oil capacity for the piece of equipment.

2. Disconnect the compressor, drier, expansion valve, or capillary tube from the system. Using flexible tubing, connect the vacated areas where the drier, expansion valve, and capillary tube were taken off line.

3. Measure the correct amount of coil flush according to the manufacturer’s recommended dosage chart. Using a hand pump, pump the coil cleaner into the system’s liquid (high-pressure) line. Connect the tubing from high- and low-side pressure to a circulating pump to create a closed-loop system; circulate the coil cleaner throughout the system for 10 minutes or longer.

Note: Pump into the low side and through the high side. If a circulating pump is not available, the coil flush can be pumped into the system as described above and left in the system for a longer period of time. A larger amount of coil flush may be necessary if a circulating pump is used.

4. Remove the tubing from the circulating pump and blow out the stem with dry nitrogen so that any remaining coil flush exits through the low-pressure side. Collect the used coil flush and compare the amount of flushing agent removed to the amount put in. Keep this fluid until completing step five.

5. Test the system for any oil, acid, or contaminants. Repeat steps two, three, and four if necessary; test again. If no oil, acid, or contaminants are found, proceed to the next step. (Some coil flushes can be reused for a second and third retrofit cleaning.)

6. Connect a vacuum pump to the system; evacuate the system to 500 microns to remove any remaining coil flush or nitrogen. Dispose of this byproduct according to federal, state, and local regulations for waste oil. Note: Oil-based flushing products cannot be vacuumed.

7. Refit the system with the proper capillary tube/expansion valve and drier according to industry standards. Note: High-moisture filter-driers are recommended.

8. Connect the compressor and recharge the system with refrigerant according to the manufacturer’s specifications.

9. Start the equipment and make any necessary adjustments.

This procedure is a general guideline. Check with the manufacturer of the unit for additional procedures or precautions regarding the use of a coil flush cleaner. This involves pumping a coil flush cleaner through a system.

Isolate the compressor by closing the discharge service and suction service valves. Disconnect the lines from the compressor and connect the hoses from the pump. Take off line accumulator, receiver and filter driers and bypass using hose sections. Clean these components separately. Pump the coil flush through the system for 10 minutes (retrofit) and 20-30 minutes for burnout.

At the end of the cycle, remove the pump inlet hose from the coil flush and continue running the pump to remove most of the coil flush from the system. Turn off the pump and disconnect the outlet hose. Blow lines clear with nitrogen (minimum of 100 psi for two minutes or more) and evacuate the system with a vacuum pump. Reconnect the system.

Publication date: 06/04/2007

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