Air Conditioning

Q. Is the retrofit market still hot?

A. According to a recent survey by the Mobile Air Conditioning Society (MACS), approximately 40 percent of the A/C work thats currently being performed is on older vehicles with R-12 A/C systems. Of these, about 9 percent were retrofitted this year to R-134a.

Most shops will encourage customers to convert their vehicles A/C system to R-134a if major A/C components such as the compressor, condenser or evaporator need to be replaced. Most new compressors and reman compressors are manufactured to be compatible with R-134a, so theres no penalty to retrofit the system if these parts are being replaced. On some older Japanese cars, the compressor seals are not compatible with R-12, which means the compressor must be replaced if the vehicles owner wants to change refrigerants.

Changing refrigerants requires recovering any old refrigerant that may still be in the A/C system, and replacing some or all of the old mineral oil in the system with the required PAG oil or POE oil.

Cooling performance with R-134a is nearly the same as R-12 on most vehicles, but some may require the installation of a larger or more efficient condenser and/or a variable orifice tube to improve low-speed cooling.

Another reason to convert is that R-134a costs less than R-12, which is becoming scarcer and more expensive as time goes on. Consumers can also purchase small 14-oz. cans of R-134a and recharge their own A/C system if the need arises, which is a plus for your do-it-yourself customers. Federal law restricts the sale of R-12 to certified professionals only.

The MACS survey also found that owners of older vehicles are still spending money to maintain and repair their A/C systems, and that many people are spending upwards of $1,000 or more to repair and retrofit older cars and trucks!

The average A/C repair job, according to MACS, was $504 for all types of service work, plus an average of $176 extra to retrofit the system after repairs were made.

Q. What kind of A/C parts are replaced most often?

A. According to the same MACS survey, these are the A/C system parts that are most often replaced:

31 percent – Compressor (17 percent due to leakage, 14 percent due to internal failure);

10 percent – Leaky hoses;

8 percent – O-rings or seals;

6 percent – Compressor clutches (worn out or failed);

5 percent – Condenser (leaks, corrosion, damage, blockages);

4 percent – Evaporators (leaks).

Knowing this may help you decide what kind of A/C parts to keep in stock.

Q. Is flushing recommended to clean dirty or blocked condensers?

A. Flushing is a controversial issue because some vehicle manufacturers endorse it, while others prohibit it. According to the MACS survey, one out of four vehicles that had A/C service work done also had their A/C system flushed either because the vehicle experienced a compressor failure or the system was contaminated with sludge or debris.

Most shops (92 percent) say they use liquid refrigerant to clean the A/C system, while 5 percent reported using an approved flushing chemical. No cleaning chemical other than one that has been approved for A/C flushing should be used to clean A/C parts. Many chemicals attack plastic parts such as orifice tubes, o-rings and hoses, and can leave harmful residues in the system that may later cause problems.

Whats more, only certain parts can be flushed. This includes serpentine-style condensers (but not parallel flow condensers), evaporators, hoses and lines. Compressors should not be flushed, nor should hoses that contain in-line mufflers or filters.

Flushing is good for removing sludge and debris from contaminated systems and for removing excess compressor oil from the condenser (if the system has been overcharged with oil, which is a common problem).

To help technicians better understand the flushing process, ACDelco has released a new A/C Flushing video (SD-AC-1.01-SUP) that is available through ACDelco distributors.

One caution with respect to flushing is that it will not remove all of the metallic debris from a contaminated system. An in-line filter should therefore be installed in the liquid line to trap any residual debris that a flush may have missed.

Q. Is dye the best way to find refrigerant leaks?

A. Ultraviolet dyes that are added to refrigerant can make even the smallest leaks clearly visible. But some vehicle manufacturers do not approve their use because they fear dye may cause problems. OEMs who currently endorse the use of dye include Ford, GM, DaimlerChrysler and Nissan. OEMs who do not currently use or endorse dyes include Honda, Mazda, Toyota, Hyundai and Mercedes. OEMs who do not use or endorse dye may not honor a compressor warranty if it fails and is found to contain dye.

Too much dye can 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 will usually cause no problems, but multiple doses over a period of time can overload the system with too much dye.

Q. Are A/C system sealers safe to use?

A. In recent years, various sealer products have been introduced to stop refrigerant leaks. Some are activated by exposure to moisture, while others stop leaks by causing seals and o-rings to swell. These products may also be used to temporarily seal evaporator pinholes and other leaks when a customer cant afford to have parts replaced.

In spite of these benefits, no OEM vehicle manufacturer currently approves of the use of any type of sealer in their A/C systems.There is some concern that sealers may gum up refrigerant recovery and recycling equipment, service hoses and test gauges. To address this issue, several companies have introduced filters to protect service equipment from sealers and dyes. Technicians often have no way of knowing if someone has added a sealer to an A/C system in an attempt to stop a leak.

Q. What about other kinds of refrigerants (other than R-12 and R-123a)?

A. Although many refrigerants have been approved by the EPA, they can never be mixed. Its illegal, potentially dangerous and can ruin a technicians AC service equipment. This includes R-134a: It cannot be mixed with R-12.

Mixing different kinds of refrigerants alters the operating pressures and can cause system problems such as a failed compressor.Of course, its okay to convert from one refrigerant to another, but before that can be done, all the old refrigerant must be evacuated (not vented) using the proper equipment.

Batteries

Q. Is cold weather harmful to batteries?

A. The chemical reactions inside a lead-acid battery are affected by temperature. As the temperature drops, it slows down the chemistry and reduces the number of cranking amps the battery can produce.

At zero degrees F, most batteries can only deliver about 65 percent of their normal cranking amps. At 20 degrees below zero, battery power is cut in half!

But when the temperature warms up again, the batterys ability to produce power returns to normal, and the battery produces the same number of amps as before.

Cold weather also increases the cranking load on the battery. Cold weather thickens the oil in the engines crankcase. This increases friction and makes the engine harder to crank. Normal cranking loads can require 125 up to 200 amps or more from the battery depending on engine displacement, compression and temperature. At zero degrees F, that number can increase 200 to 250 percent depending on the viscosity of oil in the crankcase.

Actually, hot weather is hardest on batteries because it increases the rate at which water evaporates from inside the battery.

Q. How do you determine a batterys state of charge?

A. Battery charge can be determined in several ways. Some batteries have a built-in charge indicator. If a green dot is showing in the clear plastic window, it means the battery is 75 percent or more charged. A dark indicator (no green dot) indicates a low battery that needs to be recharged and tested. A clear or yellow indicator means the water level inside the battery is low. The filler caps should be removed from the top of the battery so water can be added to bring the level back up to normal. The battery can then be recharged and tested. If the top of the battery is sealed, the battery should be replaced. Do not attempt to recharge a battery with low water because there is a risk of an explosion!

Battery charge can also be measured with a voltmeter. A fully charged battery should read 12.6 volts. A reading of 12.4 volts equals about a 75 percent charge and is good enough for further testing. But anything less means the battery is low and needs to be recharged.

If the battery has removable filler caps, charge can also be determined with a hydrometer that measures the specific gravity of the electrolyte inside the battery.

Lead-acid batteries must be maintained at or near full charge to prevent deterioration of the lead plates inside. If the battery is allowed to sit more than a couple of days in a discharged condition, the plates can become sulfated and may not fully recover when the battery is recharged. This will reduce the batterys output as well as shorten its service life.

Q. How can you tell if a battery needs to be replaced?

A. By testing it with a battery tester. If a battery is run down or dead, it may only need to be recharged. A tester will reveal if the battery can hold a charge or if it needs to be replaced.

Older-style carbon pile testers apply a fixed load to the battery while monitoring its voltage. For accurate test results, the battery must first be recharged – a process that may take half an hour to overnight depending on the chargers output and the rate at which the battery accepts the charge.

Warning: Do not attempt to recharge a frozen battery. The battery should be brought inside and allowed to thaw before it is recharged or tested.

Many electronic battery testers do not require a fully charged battery for accurate test results. Testers that measure the batterys conductance can reveal the batterys condition whether it is charged or run down. Conductance testers send a frequency signal through the battery to determine how much plate area is available to hold and deliver power. As a battery ages, its conductance declines. Shorts, opens and other cell defects also affect conductance, so measuring conductance gives an accurate indication of battery condition.

Many electronic battery testers also analyze the batterys cold cranking amp (CCA) capacity, which can be used to estimate the batterys remaining service life. Some also allow you to measure the amps drawn by the starter while cranking the engine and analyze the charging systems output under load once the engine is running. Some testers even provide a built-in voltmeter for checking connections.

Brake Materials

Q. What are ceramic brake pads?

A. The short answer is that they are pads that contain some type of ceramic fiber. The long answer is that there are literally hundreds of different friction formulas in use on vehicles today. These materials range from pads with high-content ceramic to low-metallic pads with some ceramic content to semi-metallic pads with no ceramic content. The exact recipes are all proprietary secrets, so there is no way to know how much ceramic content or what type of fibers are actually in a set of pads. All you can go by is what the brake supplier tells you on the packaging, product literature or advertising. Even then, the information thats provided may be confusing.

The term ceramic is badly misused and abused and can mean almost anything with respect to brake pads. Its like ordering pizza. Do you want mushrooms, pepperoni, sausage, extra cheese, thin crust, thick crust, hand-tossed, stuffed or what? Likewise, ceramic friction materials are all different. There are different types and shapes of ceramic fibers. Which fibers are used and how they are combined with other ingredients determines the noise, wear and braking characteristics of the friction material.

One brake supplier said that they use over 20 different ceramic formulas in their ceramic product line alone, while others use only a single ceramic formula. Those who sell single-formula ceramic linings typically suffer from high Mu Variability – thats engineering lingo for a lot of variation in hot and cold friction coefficients. This results in fluctuating stopping power as the brakes heat up. It can also lead to comebacks if your brake customer is unhappy with the way their brakes feel.

Some brake suppliers offer ceramic enhanced formulas that add a dash of ceramic to an existing conventional formula.

According to industry sources, ceramic linings are now used on 75 percent of 2004 cars and light trucks. But some linings are low-content ceramics, while others are high-content ceramics. Some formulas contain up to 30 percent iron to help dampen noise, while others use little or no iron.

Q. What are the advantages of ceramic pads?

A. It depends on the brand of ceramic pads and what is in them, but generally speaking, friction suppliers claim the following benefits for high-content ceramic pads:

Quiet operation (typically much quieter than other types of friction materials, especially semi-metallics). One of the characteristics of ceramic fibers is that they dont ring like steel fibers. Annoying brake squeal is eliminated because the ceramic compound dampens vibrations.

Smooth, rotor-friendly braking (less wear on pads and rotors).

Cleaner braking (no black brake dust to dirty up alloy wheels).

Q. Can ceramic pads be installed on any vehicle?

A. The best advice here is to follow the friction suppliers recommendations. Ceramic replacement linings are available mostly for later-model vehicles. As a rule, most friction suppliers recommend replacing same with same or better.

If a vehicle is originally equipped with ceramic pads, it should have the same type of pads installed when the brakes are relined. Aftermarket ceramic pads that are application engineered will have friction characteristics very similar to the OEM pads, and should have similar noise, wear and braking performance.

As for vehicles that are originally equipped with nonasbestos organic (NAO) pads, upgrading to ceramics can often improve stopping power and pad life.

Vehicles that are originally equipped with semi-metallic pads, on the other hand, should probably stick with semi-metallic replacement pads. Semi-metallic linings are designed for high-temperature applications. For severe-duty use, other types of replacement pads might not stand up as well. For normal driving, switching to ceramic pads may help reduce noise and extend rotor life. Ceramics also require less pedal effort then semi-metallics.

Q. Whats the difference between economy-, standard- and premium-grade brake linings?

A. Price is one difference, but of course its not the only one. Premium-grade replacement linings cost more because they generally provide better wear than standard-grade linings, and certainly much better wear than economy-grade linings. Premium linings also tend to perform better in terms of stopping distance, fade resistance, pedal feel and noise control. As a rule, premium linings will restore the like-new feeling and performance that makes most customers happy.

Brake suppliers use different grades of friction materials in their economy, standard and premium product lines – and that affects the price.

Economy linings are for bargain-shoppers who want a quick fix and little else. Economy linings should never be installed on a vehicle that has a history of eating up pads or is obviously a hard-use application. Economy linings will not provide the same durability as standard- and premium-grade linings, and may not feel, sound or stop the same as the OEM linings. Economy product lines typically use only a few friction formulas, or even a one-size-fits-all formula. But in the real world, one-size-fits-all fits some better than others. There are always compromises because of differences in vehicle platforms, braking systems, weight and usage.

Standard linings, by comparison, are for normal-duty users and provide good value for the money. They may or may not use the same basic type of friction material as the OEM linings, but they generally provide satisfactory performance.

Premium linings typically use a greater variety of friction formulas for different vehicle applications. This is called application engineered or application specific lining selection. The product engineers who develop and choose the friction materials try to closely match the braking performance, feel and noise qualities of the original equipment linings and the vehicle platforms they come on. Their goal is to equal or exceed OEM braking performance.

Premium linings cost more because of this, but are also more profitable to install for your professional customers – and experience fewer comebacks because of noise, pedal feel and performance complaints.

And thats important. According to one JD Powers survey, the most important things that brake customers want are in the following order:

1. Stopping power;
2. Good pedal feel (no soft pedal);
3. Quiet operation (no squeals or other objectionable noise);
4. No brake pulsation (which is a function of rotor wear and runout);
5. Durability.

Q. What causes brake squeal?

A. High-frequency vibrations. When the brakes are applied and the pads contact the rotors, tiny surface irregularities in the rotors act like speed bumps causing the pads to jump and skip as they scrape against the rotors. This, in turn, causes the pads to shake and vibrate in the calipers and against the caliper pistons. It also causes the calipers to shake and vibrate on their mounts and bushings. The greater the play between all of these parts, the greater the amplitude of the vibrations and the louder the squeal.

Semi-metallic pads tend to be noisier than ceramic, low-metallic and nonasbestos organic (NAO) friction materials. The sound qualities of any friction material depends on the fillers, lubricants and other ingredients that go into the mix. Some manufacturers add graphite and other materials to pads to dampen noise.

The design of the pads also influences their ability to suppress noise. If the leading edge of the pads has a sharp edge, it increases the tendency to grab and bounce more than if the leading edge is chamfered. Thats why most premium-grade brake pads have chamfered edges. The pads may also have a slot down the middle to increase flexibility, cooling and venting. Some pads also have integrally molded shims and a multi-layer construction to reduce noise.

Some friction suppliers use Transfer Film Technology (TFT) to prevent noise. TFT is not a coating on the pads but part of the friction material itself.

As the pads wear, they continuously transfer a very thin film to the rotor surface. This film, which leaves a dull gray coating on the rotors, fills in tiny imperfections in the rotor surface to make it smoother and more compatible with the pads, thus eliminating squeal-producing vibrations.

The rhythmic vibrations of the pads rubbing against the rotors also creates harmonic vibrations in the rotors that causes them to ring like a cymbal. Researchers have found that rotor vibrations are not uniform all the way around a noisy rotor. The rotor has certain spots or nodes that oscillate more than other areas. By redesigning the casting and changing the location of the cooling fins between the rotor faces, some of this noise can be tuned out (a good reason to use replacement rotors that have the same cooling configuration as the original.)

Even the metallurgy of the rotors makes a difference. Some grades of cast iron are quieter than others.

Rotor finish also affects noise. The smoother and flatter the surface, the less the likelihood of the pads chattering and dancing as they ride across the surface. The rotors should be resurfaced when the linings are replaced if the rotors are not smooth and flat. Light sanding with a flexible abrasive brush after the rotors have been turned will improve the surface finish even more and provide an extra degree of assurance that the rotors will remain noise-free.

Engine Management

Q. If a vehicles Malfunction Indicator Lamp is on, will reading the Diagnostic Trouble Code (DTC) with a scan tool tell me which part needs to be replaced?

A. Indirectly it can, but the code by itself only tells you which circuit or system is involved. Whats more, some codes only describe a condition and dont give you any clues as to what might be the cause.

A cylinder misfire code, for example, tells you a cylinder is misfiring but does not tell you why or which parts may be involved. The misfire may be caused by a worn or fouled spark plug, a bad plug wire, a weak or faulty coil if the engine has a distributorless ignition system with multiple coils, a dead or plugged fuel injector, a burned exhaust valve that is leaking compression, or a leaking head gasket. Any of these can cause a misfire, so additional diagnosis is needed to isolate the fault before any parts can be replaced.

Q. What is flash reprogramming?

A. Its a technique for updating or recalibrating a vehicles Powertrain Control Module (PCM), or any other onboard module that has this feature can be accessed with a specially-equipped scan tool. Flash reprogramming is done to cure driveability and emissions problems, to calibrate new and reman PCMs, and to change fuel and ignition curves and other functions for performance applications.In the early 1990s, some vehicle manufacturers began adding Electronically Erasable Program Read Only Memory (EEPROM) chips to the circuit boards of their PCMs. Prior to this, the only way to change the PCMs programming was to physically remove the old PROM chip and install a new one.

With programmable PCMs, updates and changes can be installed electronically in a matter of minutes using a pass-through scan tool, a personal computer and new software downloaded from the vehicle manufacturer. If a PCM is being custom modified for a performance application, the software changes would be made by somebody who knows how to hack into the PCM using special access codes. This requires a high level of expertise and is not approved by the OEMs.

There are also special aftermarket performance scan tools that allow a user to get into a PCM and play around with the spark advance, fuel mixture and other functions such as the engine rev limiter, vehicle speed limiter, torque converter lockup, etc. The tools are available from several camshaft manufacturers and are necessary to make changes to the PCM when a performance cam is installed in an engine.

Some remanufacturers who supply reconditioned PCMs now flash program PCMs for specific vehicle applications. But to do this, they need three critical pieces of information: the vehicle identification number, the type of transmission and the emissions type.

Q. What do I need to flash reprogram a PCM?

A. You need three things: a scan tool or J2534 pass-through device that is flash capable; a Windows 98 or higher PC with a modem and Internet access for downloading the flash software from the vehicle manufacturers website; and a subscription to the manufacturers database so you can access the software. Other items that are needed include a cable to connect the PC to the scan tool or J2534 pass-through device, and a cable to connect the scan tool or J2534 pass-through device to the OBD II connector on the vehicle.

For GM applications: you need a Tech 2 scan tool or Vetronix Mastertech, or aftermarket scan tool with flash capability.

For Ford applications, you need a Ford New Generation Star (NGS) scan tool, or aftermarket scan tool with flash capability.

For Chrysler applications, you need a Diagnostic and Reprogramming Tool (DART). Chrysler dealers use the Mopar Diagnostic System (MDS2) and DRB III scan tool. Or, you can use an aftermarket scan tool with flash capability.

For import applications, you need whatever factory scan tool the dealer uses, an aftermarket scan tool with reflash capabilities for that vehicle, or a J2534 pass-through device that will work on the vehicle.

The flash procedure usually takes only a few minutes and is similar to installing new software into a computer. The only difference is that youre downloading the new software through a modem and scan tool into the vehicles PCM through the OBD II diagnostic connector.

Exhaust

Q. Which parts in the exhaust system are most likely to fail?

A. Drive any vehicle long enough, and it will eventually need a new muffler, exhaust pipes and converter. The more the parts are exposed to road salt, moisture, road hazards and severe vibration, the more likely they are to fail.

Exhaust system parts live in a very corrosive environment. The hot exhaust gases that exit the engine pass through the catalytic converter where some of the byproducts of combustion are changed into sulfuric acid. The acid combines with the moisture in the exhaust and eat away at the muffler and pipes from the inside out. Especially vulnerable to this type of corrosion are mufflers and resonators located behind the rear wheels where exhaust temperatures are cooler and the potential for corrosion is higher. When the engine is shut off, the gases cool, condense and puddle inside the system eating away at the metal from the inside out. Short-trip driving is especially hard on the exhaust system because it never gets hot enough to dry out all the moisture.

The stainless steel exhaust systems that are used on many late-model cars and trucks are corrosion-resistant and may last seven to 10 years before they fail. Theyre covered by a new car bumper-to-bumper 3/36 warranty, but beyond that, anything can happen. Catalytic converters are under warranty for eight years or 80,000 miles.

Heat and vibration from normal driving is also hard on pipes, connectors and flanges. Stainless steel resists corrosion, but it is also hard and brittle. Its not unusual for fatigue cracks to form that eventually lead to exhaust leaks.

With transverse-mounted engines, the head pipe must have some type of flexible coupling or section to handle engine movement. Many failures occur in this area because this is the most highly stressed part of the system – and also one of the most expensive to replace. Head pipes with flex sections are commonly used on import vehicles and have a high failure rate.

Q. Why are exhaust leaks so dangerous?

A. Ever heard of carbon monoxide? Its an odorless, invisible gas that is a byproduct of combustion – and it can kill in minutes!

It doesnt take much carbon monoxide to make a driver dizzy or cause him to pass out. Fumes that enter the passenger compartment can be deadly, so warn anyone who has an exhaust leak what theyre risking and to make the necessary repairs.

Leaks can occur anywhere from the exhaust manifold gaskets to the tailpipe. Exhaust manifold leaks are quite common and occur because the gasket has failed from thermal stress and scrubbing. A customer who is replacing an exhaust manifold gasket will probably also need new exhaust manifold bolts.

Q. Exhaust noise from the engine compartment usually means what?

A. A leaky exhaust manifold gasket, a cracked exhaust manifold or a leaky head pipe connection. Cracks in exhaust manifolds are a common problem on some engines. An exhaust manifold goes from stone cold to hundreds of degrees in a matter of seconds when an engine is first started. Stomping on the throttle and working the engine really hard sends manifold temperatures soaring. This puts a lot of thermal stress on cast manifolds, which eventually leads to cracks and exhaust leaks. Cast iron does not weld very well in this kind of application, so the best fix is to replace the manifold with a new one. New manifolds should always be installed with new gaskets and bolts.

Q. Whats the number one killer of catalytic converters?

A. Ignition misfire. A single misfiring spark plug can allow enough unburned fuel into the exhaust to overheat and damage the converter. It can make the converter run so hot that the catalyst inside the converter melts causing a partial or complete blockage in the exhaust system.

Theres no way to clean or unplug a damaged converter. Replacement is the only fix. But a new converter should not be installed until the underlying cause of the failure has been diagnosed and repaired. The cause may be a fouled spark plug, bad plug wire or dead coil on an engine with a distributorless ignition system or coil-on-plug ignition.

Converter overheating can also be caused by a burned or leaking exhaust valve that allows unburned fuel to pass through the engine.Contamination is another common cause of converter failure. Contaminants include phosphorus from burning oil (worn valve guides or seals, or worn piston rings or cylinders), silicone from internal coolant leaks (bad head gasket or cracks in combustion chamber) and high levels of sulfur in gasoline.

Replacement converters must be the same basic type as the original (two-way, three-way or three-way plus oxygen), and be installed in the same location in the exhaust system. Replacing a converter with a straight pipe or test pipe is illegal.

Fuel Pumps

Q. How much fuel pressure should a good fuel pump produce?

A. It depends entirely on the vehicle application and fuel system.

Fuel-injected engines require a lot of pressure to operate the fuel injectors. The pump has to push fuel from the tank to the injector supply rail on the engine, and then force it through each injector when the injector opens to spray fuel into the engine. The amount of pressure is critical and must be within specifications for the injectors to deliver their normal dose of fuel. The amount of pressure required may vary from 35 to 85 pounds of pressure depending on the system, application and load on the engine.

On older carbureted engines with mechanical fuel pumps, much less pressure (2 to 6 lbs.) is needed because all the pump has to do is keep the carburetor bowl filled with gasoline. Intake vacuum sucks the fuel through the carburetor.

What happens if fuel pressure is not within specifications? Too much fuel pressure in a fuel-injected engine will create a rich fuel condition, causing an increase in fuel consumption and carbon monoxide (CO) emissions. An engine thats running really rich may also experience a rough idl