When an air conditioning compressor fails, many people think the only part that needs to be replaced is the compressor. They may not realize that a compressor failure is often a major catastrophe in terms of the damage it causes through the A/C system. Consequently, if the only part they replace is the compressor, it’s likely the A/C system will experience more problems down the road — including another failed compressor!
Nobody wants to replace A/C parts that seem to be okay, especially if those parts cost upwards of several hundred dollars. But unless they replace certain parts, they are going to have even more repair bills. Here’s why: When a compressor goes bye-bye, it often regurgitates a lot of metallic debris into the A/C system. Most of this junk blows out through the discharge port and collects in the condenser (the large heat exchanger that sits in front of the radiator). But some of it may also blow back through the compressor’s inlet port into the suction hose. Debris in the suction hose is especially bad because as soon as the new compressor is installed and starts to run, it will suck the debris right back into itself and likely suffer damage or seize up. Debris can damage any type of compressor, but scroll-style compressors are especially sensitive to any contamination inside the A/C system.
As for the debris in the condenser, it won’t stay put either. The nooks and crannies in the condenser will trap a lot of the contaminants, but some of the junk will be carried out of the condenser by the liquid refrigerant. It will travel to the next component in the A/C system, which is the orifice tube or thermal expansion valve (TXV), where it may cause a blockage. At best, the A/C system will stop cooling. At worst, the blockage will cut off the lubricant that circulates with the refrigerant, starving the compressor for oil and causing it to fail again.
There are some additional parts that should be flushed or replaced if a compressor has failed and there is debris or sludge inside the A/C system. The same goes for any compressor failure that was the result of black sludge in the system.
Parts that should be replaced in these instances include the orifice tube or thermal expansion valve, the accumulator or receiver-drier (I’ll explain why in a minute) and any hose that contains a “muffler” (a muffler may be used with a piston style compressor to dampen pressure pulsations in the system for quieter operation, but the muffler may trap debris that could dislodge and cause future problems). The hoses and evaporator can be flushed (more on this in a minute) and the condenser may have to be replaced if it is a type that cannot be completely flushed. Additional parts that can be recommended include a filter for the liquid line, and an inlet filter screen for the suction hose.
Your customer will also need the proper compressor lubricant. This would be mineral-based compressor oil for an older pre-1994 vehicle with a R-12 system — but only if the system is being recharged with R-12 refrigerant. If the vehicle is a 1994 or newer model with an R-134a A/C system, the compressor will require the specified PAG lubricant (there are different viscosities so make sure your customer gets the correct one for the application). If an older vehicle is being retrofitted (converted) from R-12 to R-134a, it will require either a PAG oil or POE oil.
Here’s something else you should know. Replacement compressors may or may not contain oil. If it does contain oil, it should be the proper type specified for the compressor and refrigerant. But on older applications that are being retrofitted to R-134a, the compressor may be shipped with mineral oil. This should be drained and replaced with PAG or POE oil.
Over time, moisture contamination in an A/C system will form corrosive acids that attack metal surfaces and breaks down the lubricating qualities of the compressor oil. The result is a dark colored sludge called “Black Death” that can gum up the orifice tube or expansion valve and ruin the compressor.
How does moisture get in the system? Humidity in the air can slowly infiltrate microscopic pores in seals and hoses over time (we’re talking years, in most cases). But a refrigerant leak due to a bad seal, hose or hose connection, or a pinhole leak in the evaporator or condenser can allow air and moisture to seep in as refrigerant leaks out. Moisture can also contaminate the system very quickly if the A/C system is discharged and a hose is disconnected and left open for more than a few hours (which often occurs when repairs are made). The higher the relative humidity, the faster the rate of contamination when the system is left open.
Another source of moisture contamination can be bad refrigerant. Virgin refrigerant contains no air or moisture. Neither does recycled refrigerant, provided it is recycled properly and the recycling equipment is maintained and working correctly. But if there’s a problem with the recycling equipment, the filters haven’t been replaced or the storage tanks have not been purged, residual moisture from one vehicle can be passed to the next via the recycled refrigerant. Consequently, if the A/C system is recharged with bad refrigerant, it’s doomed from the get-go.
A/C systems do have a limited amount of built-in protection against moisture contamination. It’s called desiccant. The desiccant consists of moisture-absorbing crystals in a small bag or pouch inside the accumulator or receiver-drier. The desiccant can absorb and hold up to several ounces of moisture, which is adequate to protect the system under normal conditions. But it isn’t enough to protect the system if there is a refrigerant leak or a hose is left open overnight. That’s why you should recommend replacing the accumulator or receiver-drier if the A/C system has had a moisture contamination problem.
Most of the moisture that enters an A/C system through an open hose during normal service procedures can be removed by vacuum purging the system prior to recharging it with refrigerant. This step is something every professional technician should do prior to recharging an A/C system because it pulls out both air and moisture. You don’t want air inside an A/C system because it displaces refrigerant and reduces cooling efficiency. Air also makes the compressor work harder and run hotter. This can make the system noisy and may eventually lead to premature compressor failure.
Unfortunately, few do-it-yourselfers have access to an A/C vacuum pump and probably wouldn’t know how to use it properly even if they had one. Vacuum purging requires pulling a high vacuum (29 inches Hg) on the system and leaving it under the vacuum for 30 minutes to an hour or more (longer is better in areas of high humidity). Even then, there may be some residual air and moisture that remains trapped in the compressor oil. But as long as most of the air and moisture are pulled out, it should cause no problems.
The issue of flushing is a controversial one. Some vehicle manufacturers say contaminated parts can be cleaned by flushing them with R-134a refrigerant (GM, for example), or an “approved” flushing chemical (never ordinary parts cleaners or other solvents that may damage parts or leave residue in the system). Closed-loop flushing is usually recommended and parts must be thoroughly air dried before they are returned to service. Blowing them out with shop air is not recommended because shop air often contains oil and moisture.
Other vehicle manufacturers say flushing is an absolute no-no because it may not remove all of the contaminants and may introduce foreign chemicals into the system that could cause problems later.
Proponents of flushing say it is a much less expensive alternative to replacing expensive parts such as a condenser. But they also recognize the fact that most late-model condensers are not flushable, either because the condenser has a parallel flow design, or because it has flat extruded tubes with tiny internal passages that are nearly impossible to flush out. Flushing is only an option for older tube-and-fin serpentine style condensers with large round tubes. The same goes for evaporators.
Hoses can be flushed, provided they do not have mufflers. But other parts such as orifice tubes, expansion valves and the compressor itself should not be flushed. Replacement is the only option for these parts if the system is contaminated with debris or sludge.
Flushing can also be used to remove residual oil from hoses and the condenser, and may be necessary if a system has been overcharged with too much oil or the wrong type of oil. In this case, no parts have to be replaced.
OTHER KINDS OF PART FAILURES
Sometimes a compressor will just wear out from old age. Other times, it may lock up because it has run out of lubricant. In cases of lubricant-related compressor failure, the underlying cause may be the wrong type of compressor oil in the system, or a refrigerant leak that has also caused a loss of oil. If the missing oil is not replaced when the A/C system is recharged, the compressor may not get enough lubrication and fail. The amount of oil in the system is critical and should not be more or less than the recommended amount.
In the case of a refrigerant leak, you should recommend using leak detection dye to find the problem so it can be fixed. The dye glows under ultraviolet light and will reveal even the smallest leaks.
Caution: A small amount of dye is all that’s needed to reveal most leaks. Overcharging the system with too much dye may gum up the orifice tube or expansion valve, or interfere with compressor operation or lubrication.
Evaporator leaks are often the result of internal corrosion due to contaminated refrigerant or electrolysis. Evaporators are difficult to replace because of their buried location inside the HVAC assembly under the dash. One option here is to use an A/C system sealer product to temporarily plug the leak.
A/C SEALER PRODUCTS
A/C sealers come in three varieties. Some contain organic silicones and sealing compounds that solidify when they react with air and moisture. This type of sealer circulates with the refrigerant until it encounters a leak. As it starts to escape through the leak, it reacts and turns hard to plug the leak. Another type of sealer contains chemicals that cause o-rings and seals to swell. This can stop seal leaks but has no effect on leaks in metal tubes, or evaporator or condenser leaks. A third type of sealer product combines both approaches and seals both kinds of leaks.
Sealers are controversial because many technicians fear sealers may gum up their refrigerant recovery machines (hose filters are available to protect their equipment). Others say sealers may gum up the system or compressor, or cause seals to swell too much. Because of this, most compressor manufacturers will not honor their warranties if a compressor has failed and sealer is found inside the unit. In spite of these issues, the companies that make sealer products insist their products are safe to use and provide a simple, inexpensive fix for many common leaks.
We’ll wrap up this article on A/C parts sales with a few words about selling refrigerant. Current EPA rules do not restrict the sales of R-134a refrigerant or other “alternative” refrigerants, but the rules do prohibit selling R-12 to anyone who is not a “certified” technician. The California Air Resources Board, however, is now considering a ban on the sale of R-134a to non-certified technicians as well.
Though not a rule, the automakers have said the only refrigerant they officially endorse for “retrofitting” (converting) older R-12 A/C systems is R-134a. They say this reduces confusion and the risk of cross-contamination when servicing vehicles. Other alternative refrigerants that meet the EPA’s “SNAP rules” are available and can be used in place of R-12 in older vehicles. But these products should not be used in newer vehicles with R-134a A/C systems. Mixing different types of refrigerants in a vehicle is also prohibited by the EPA. Before one type of refrigerant can be substituted for another, all of the old refrigerant must be recovered. Venting is prohibited.
Flammable refrigerants that contain propane, butane or other hydrocarbon compounds are also illegal for automotive use. If a refrigerant leak occurs in the passenger compartment, a small spark could ignite the vapors and turn the car into a bomb. There’s also a risk of fire if the vehicle is hit in the front and the A/C condenser is ruptured.