AC Update: Finding and Fixing Leaks – UnderhoodService

AC Update: Finding and Fixing Leaks

Finding refrigerant leaks is a major aspect of A/C service. It makes no sense to recharge a leaky system with refrigerant if it will soon leak back out. Ultraviolet dyes can make even the smallest leaks clearly visible. But not all OEMs approve of their use. The domestic OEMs (Ford, GM and Chrysler) all use and approve the use of dyes. The only import vehicle manufacturer who has publicly endorsed the use of dye is Nissan (since 1999).

Honda, Mazda, Toyota, Hyundai and Mercedes-Benz currently do not use or endorse the use of dye to find leaks. One reason they may be leery of dye is because using too much may dilute the compressor lubricant and increase the risk of compressor noise and failure. The standard recommended dose is only one-quarter ounce. A second dose won’t usually result in any problems, but multiple doses over a period of time can overload the system with dye and cause trouble.

Evaporator Issues
Evaporator leaks can be expensive to fix because the labor alone may be eight to 12 hours or more depending on the application. For customers who can’t afford such a repair, a sealer may offer a less expensive fix – though no promises should be made as to how long the leak repair will hold or if it will seal the leak at all.

When evaporator leaks are caused by external corrosion, the culprit is often an accumulation of leaves and debris in the evaporator case. The debris traps moisture and promotes metal corrosion. It may also jam the fan and cause noise or blower motor failure, too. Some vehicles do not have screens to keep debris from entering the HVAC inlet. Others have cabin air filters that not only stop debris, but also dust, pollen, bacteria and even odors from entering the passenger compartment. Many motorists have no idea if their vehicle has a cabin air filter or not, let alone where it might be located or how to replace it.

Cabin air filters are usually positioned behind the glove box or at the base of the windshield in the cowl area. The cabin air filter is an important filter to maintain because restrictions can affect the operation of the climate control system, yet it is often overlooked when other A/C service work is done. The recommended replacement interval for an activated carbon odor absorbing cabin filter is typically once a year or every 12,000 miles. Plain pleated paper dust filters can usually go two years or more before a change is needed.

Compressor Replacement
The only rule you have to know about replacing compressors is that there are no rules. Some compressors are shipped dry, others are shipped with assembly oil (which must be drained prior to installation) and others are shipped with mineral oil for R-12 applications, a specific type of PAG oil for OEM R-134a applications, or polyester POE oil for a retrofit. Make sure you read the instructions that come with a compressor so you can determine if oil needs to be drained or added before installation.

Most compressor manufacturers will void their warranty if the wrong oil is used, if the compressor is installed in a dirty system (contaminated systems must be flushed with refrigerant or an approved solvent, and a filter installed), if a non-approved flushing chemical is used to clean the system, or the accumulator or receiver-drier is not replaced.

Some replacement compressors may not look or fit quite the same as the original. This should not affect cooling performance, but can create installation hassles if you have to re-route hoses or modify brackets.

Some compressors come with new clutches and others do not. Most experts recommend replacing the clutch on high-mileage vehicles to minimize the risk of a comeback. Clutches do wear over time and can cause cooling problems if they slip or fail.

Condenser Concerns
You may have to replace a condenser if it is leaking, damaged or the A/C system is contaminated. If the condenser is not the type that can be completely flushed, don’t take chances. Replace it.

Replacement condensers should have the same cooling capacity as the original to maintain the same cooling performance. With some retrofits, installing a larger or more efficient condenser will help offset the slight loss in cooling effectiveness when switching refrigerants.

Final Charge
Charging accuracy is also essential to get the best cooling performance from an A/C system. The refrigerant capacity of most passenger car systems today is only about

1-1/2 lbs. or less. Consequently, it is easy to accidentally over-charge the system. Charging equipment with long hoses may contain 4 to 6 oz. of refrigerant in the hoses. If this extra amount is not taken into account, you may end up adding too much refrigerant.

Complete evacuation of the system is also a must before you add the refrigerant. Air is a non-condensable gas that reduces the operating efficiency of the system. Moisture is a contaminant that reacts with refrigerant and compressor oil to form acids and sludge. If not removed, air and moisture will cause problems sooner or later. The normal vacuum cycle during refrigerant recovery is only about five minutes, which is not long enough to thoroughly evacuate all the air and moisture from the system.

Most experts say it takes 29.7 inches or more of vacuum for 45 to 60 minutes to completely purge the system, 60 to 90 minutes for dual (front/rear) A/C systems, and up to two hours to purge a contaminated system in a colder or humid climate. The accumulator or receiver drier should also be changed if the system has been open or without a charge for a long period of time.

Another suggestion: If air contamination has been causing noise or other problems, deep vacuum purge the system and recharge it with virgin refrigerant rather than recycled refrigerant. Why? Because recycled refrigerant may contain 2-3% air.

In recent years, various sealer products have been introduced to stop refrigerant leaks. Such products are marketed as an inexpensive way to fix troublesome refrigerant leaks. Some of these products are activated by exposure to moisture, others stop leaks by causing seals and O-rings to swell, and some combine the two approaches.

The main drawbacks of using a sealer are the risk of a comeback if the sealer fails to stop the leak, clogging up service gauges and recovery/recycling equipment (filters are available to protect your equipment), and plugging the orifice tube if the system is contaminated with air and/or moisture. Because of these risks, no vehicle manufacturer, import or domestic, currently approves the use of sealer products. Yet, there is a demand for these products.

The best cure for a leaky evaporator is to:

  1. Replace the evaporator with a new one;

  2. Thoroughly flush the hoses and condenser to remove as much contamination as possible;

  3. Replace the accumulator or receiver drier (which contains a bag of moisture-absorbing desiccant to protect against further corrosion);

  4. Replace the orifice tube since the old one is probably dirty or plugged;

  5. Install an in-line filter in the liquid line to trap any contaminants that were not removed by flushing;

  6. Suck all the air and moisture out of the system with a vacuum pump once everything has been reassembled; and

  7. Recharge the system with a fresh dose of clean refrigerant and compressor oil.

Educate Your Customers about Hydrocarbon Refrigerants

As a shop owner or technician, you can provide common-sense tips to your customers regarding protecting the environment, without endangering safety. According to the Mobile Air Conditioning Society (MACS), vehicle manufacturers, automotive parts suppliers, the U.S. Environmental Protection Agency (EPA), and other organizations are warning car and truck owners to avoid the use of flammable hydrocarbon refrigerants, which are being marketed on the Internet, at flea markets and swap meets, and in some service shops, but are not authorized for this use.

In the U.S., it is illegal to use hydrocarbon refrigerants to replace CFC-12 used in cars manufactured before 1994. Hydrocarbon refrigerants used in newer vehicles designed for refrigerant HFC-134a will void the air conditioner warranty and may endanger service technicians. Leaking air conditioning systems charged with hydrocarbons pose serious risks of fire or explosion under the hood or inside the passenger compartment.

“Professional service protects the environment and saves money,” said Elvis Hoffpauir, president of MACS. “Hydrocarbon refrigerants are dangerous products being sold to unsuspecting consumers.”

So what are some things to inform car owners who want to help protect the environment? Explain to them to:

  • Hire a certified technician to service your A/C system using quality parts.

  • Insist that leaks be repaired before systems are recharged.

  • Retrofit CFC-12 systems to HFC-134a.

  • Service your HFC-134a air conditioner only with HFC-134a.

  • Have your refrigerant tested for hydrocarbons if you suspect improper service.

Source: Mobile Air Conditioning Society

Tech Q&A

Q. How can I tell if an A/C system is contaminated?

A. The presence of particulate matter in the compressor ports and any other internal A/C components will tell you there is a contamination issue. (Note, however, that some aluminum chips in the first window of the orifice tube are normally left over from the manufacturing process and are not indicative of failure.) The presence of desiccant beads in the system indicates the desiccant bag has ruptured. In this case, the system should be serviced in the same manner as it would following a catastrophic compressor failure.

Note: Always refer to the vehicle manufacturer’s service manual for the specific requirements of a cooling system or A/C repair.

Information courtesy of Visteon Corporation

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