UH OH! YOU BROKE SOMETHING - Constant...

MACS Service Reports is the offi cial technical publication of the Mobile Air Con-ditioning Society Worldwide, Inc., P.O. Box 88, Lansdale, PA 19446. The mate-rial published in MACS Service Reports expresses the views of the contributors and not necessarily that of MACS. Every attempt has been made to ensure

the accuracy of the content of MACS Service Reports. MACS, however, will not be responsible for the accuracy of the information published nor will MACS Worldwide be liable in any way for injury, labor, parts or other expenses resulting from the use of information appearing in MACS Service Reports.

April 2017 1 MACS Service Reports

Total Vehicle Climate and Thermal ManagementTM

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Ugly happens in many ways when you’re working on a car, and although you learn to accept some of the damage, it hurts both your work schedule and your bottom line. The situation with today’s more complex vehicles raises a lot of “what do I do now?” questions.

Underhood is a real challenge. Components are “layered” into place, so you often face the challenge of removing several parts before you can reach the HVAC or cooling system ones that you have to service or replace. More and more cars and light trucks are turbocharged, and the trend is solidly in that direction. Turbos provide power boosts on smaller-displacement engines without noticeable effects on fuel economy, because most of the boost occurs outside the range of EPA economy testing.

But a turbo is not just a single assembly. It includes lots of hoses for air and coolant, and electro-mechanical parts, includ-ing solenoids. So you have to be really careful. A recent General Motors study showed that technicians often cause damage to them, and then face the problem of “restoration.”

General Motors has been warning about the 1.6-liter turbo in the 2016 Buick Cascada convertible, which seem to have been coming back from dealers with damage to the solenoid vacuum port fi tting on the wastegate actuator and the bypass valve port fi ttings. A friend of ours who has worked in the GM warranty returns department tells us that when a less-than-scrupulous dealer tech makes a mistake, he might do something additional (and untoward) to a component to “create” a warranty failure. An independent garage technician can’t get away with that. So

if you suffer a clumsy day and damage a turbo, you can’t just mount a new turbo assembly. In the case of the GM turbos, and likely other makes, there are service parts kits for the bypass valve, wastegate solenoid and wastegate actuator. See FIG. 1. It’s not a good day even to have to spring for any of those items, but it sure beats a new turbo assembly—what you get might be a stripped assembly anyway, with those parts listed for change-over. Yes, you have to be more careful working under the hood today, but at least alternatives exist. ■

April 2017UH OH! YOU BROKE SOMETHING

Figure 1: It’s important to be careful with removal and reinstallation of under-hood and underdash parts from today’s crowded areas, to avoid costly breakage. This underhood 1.6-liter GM turbo is an example. Fortunately, among the often broken parts are the solenoid port fi ttings on the wastegate actuators (labeled A) and the bypass valve port fi ttings (B). Fortunately, there are service parts kits for the bypass valve, wastegate solenoid and wastegate actuator, to keep the damage within reason.

By Paul Weissler – MACS Senior Correspondent

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ALSO INSIDE THIS ISSUE:Yes, turbos are new centers of attention ......................................................................................................................... 2

Evaporator failures—the hvac case “shortcuts” ............................................................................................................ 2

And now for an evaporator leak we’d like to talk about ................................................................................................. 3

What? Another General Motors anti-freeze .................................................................................................................... 3 Other antifreezes ............................................................................................................................................................... 4

We’re sounding like a “broken record” ........................................................................................................................... 5

The new denso compressors – discussion by popular request ................................................................................... 7

Oil separator ....................................................................................................................................................................... 8

Refrigerant blows open the pressure relief valve ........................................................................................................... 8


The more hoods you raise on late-model vehicles, the more likely you are to see a turbocharged engine. This means that there’s another heat exchanger at the front of the engine for you to pay attention to when there’s an air conditioning-related airfl ow issue to diagnose. And because most of the turbos are water-cooled, they’re an-other source of possible leakage.

Ford has become the “turbo leader” among U.S. brands, featuring its “Eco-Boost” label. Turbos help car makers increase fuel economy because the engine itself is of small displacement, so “it’s performance when you fl oor the pedal, but not when you’re doing ‘normal’ driv-ing and highway cruising,” which is when most of the tests measure emissions.

Charge air coolers that use ambient air for cooling are primarily in large trucks; cars and small crossovers/SUVs use water-cooled and have for many years (think Subaru). The Ford Eco-Boost engines are a modern ex-ample, and they should be kept in mind for cooling sys-tem issues. Example: the 2014-on Ford Fusion with the 1.5-liter direct injection EcoBoost turbo (plus the 2017 Es-cape with the same engine), which occasionally has suf-fered from white smoke (certainly a coolant tipoff) and low coolant level. The problem turns on the MIL and logs fi ve misfi re codes, plus one or two overtemperature codes (P0217—coolant, and P1299-cylinder head over-temperature active).

The basic check is a cooling system pressure test. If the system doesn’t hold pressure, you have to go through

normal cooling system diagnostics. If it does hold pres-sure for at least two minutes, remove and inspect the charge air cooler at the lower edge, where you’ll likely fi nd contact with an intake manifold bolt that backed out and damaged it (FIG 2). Ford recommends replacing the manifold and the charge air cooler. If all you fi nd is leak-age from the CAC, replace that. Service details are in a Ford bulletin, so once more we won’t go into them, or list all the part numbers. The point is that turbos and CACs are now a major factor in cooling system service and even A/C performance. ■

YES, TURBOS ARE NEW CENTERS OF ATTENTION

EVAPORATOR FAILURES—THE HVAC CASE “SHORTCUTS”

Figure 2: Damage to this lower edge area of the charge air cooler on 2014-17 Ford Fusions with the 1.5-liter EcoBoost turbo, that results in coolant leak-age, likely was caused by a bolt backing out from the intake manifold. If this happens, both intake manifold and charge air cooler must be replaced.

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Evaporator leaks are not only the toughest to positively identify, but usually the toughest to repair, because of the access issue. On most late-model cars there’s a cross-body brace under the dashboard that makes it necessary to remove the dashboard, and that often is a full-day job, or even longer. So you want to make sure the problem really is the evaporator. What can be even worse is when the evaporator is “just” a half-day job—still not inconse-quential—and the shop goes ahead with an R&R and dis-covers nothing wrong with the evaporator.—talk about a reason for a grown man to cry.

Because so many evaporators are so diffi cult, there’s a “cottage industry” in shortcuts for an R&R. Almost ev-ery HVAC technician can tell you how he turned a partic-ular 10-hour evaporator case R&R into a great time-saver with his secret method.

Some of the shortcuts involve careful bending to clear a

beam so you don’t have to remove it. But there also have been a few that involve cutting a bolt head instead of re-moving a bolt you can’t reach with any known wrench or alternative. Or the technician can get a particular bolt out, but during the HVAC case installation, there is ab-solutely no way he can get it back in. Because the part is held by other bolts, he is confi dent it won’t loosen (badly?) and create a problem. However, there’s soon an offensive rattle and he has to explain to the customer that he saved him hours of labor charge and the rattle should be no real issue. Well maybe. We have heard of using that bolt with the cut-off head as a pilot, so at least it functions as a guide into a mounting hole. We think we’ve gone as far as we can with this. It comes down to knowing the customer, and having a good “feel” for that missing bolt. ■


The evaporator is an object of high suspicion when there’s a small but still needs-attention refrigeration system leak, and the shop can’t fi nd it at an O-ring joint or compressor (shaft seal or head cover seal). Of course, we’ve covered many causes of hard-to-fi nd leaks of this type, which often turn out to be rub-throughs on refrigerant lines buried out of sight. And on sys-tems with rear evaporators, the underbody refrigerant lines fre-quently hold the cause.

With today’s sensitive-but-not-too-sensitive electronic leak detectors, going through the A/C registers for evaporator access is a common procedure, and although it seems to work on some cars, it’s hardly universal on all. At one time a leading maker of HVAC cases was considering marking each case with a place to make an access hole, using a hole saw, that would permit use of borescope and leak detector probes. Many technicians remove the evaporator temperature sensor to gain access to the evapo-rator area, and just probe the evaporator core face with an elec-tronic leak detector.

Nothing wrong with that, of course, provided it’s an SAE cer-tifi ed J2791 detector. But combining with borescope inspection is even better, when it confi rms the leak is actually from a local-ized area on the evaporator core face. We say this because if the probe tip lands on case joints or the gasket surfaces, the detector may be responding to emissions from the elastomer used. That used to be more of an occurrence than we hear about today, but the borescope confi rmation can’t hurt.

On vehicles with rear evaporators, we just heard of another leak source, at the rear evaporator. But although it was anything but conventional, it actually was a rear evaporator version of a leak we had encountered several years ago on the front evapora-tor of a Volvo.

In this case, the leak affects 2013-on General Motors full-size crossover SUVs, specifi cally the Chevy Traverse, Buick Enclave and GMC Acadia. The symptom is a low refrigerant charge that the technician traces to the rear HVAC system. Although these rear systems don’t exactly fl y out of the rear quarter panel, they are a lot easier to service, and some partial disassembly should provide good access. In the case of these GM SUVs, the access

to the evaporator is by removing the rear blower control module (accessible through the rear console) and inserting the probe of an SAE J2791 leak detector.

What could cause the rear system evaporator core to develop a leak? Well, it’s surely corrosion, but why and how at the rear system. Turns out that the rear blower motor has brushes (there are brushless motors, but not this one). As the brush wears in against the commutator, it picks up copper particles from it, and those copper particles blow off the brushes and onto the evap-orator—aluminum and copper react to cause corrosion and a leak results.

Interestingly, there’s nothing functionally wrong with the blower motor after it wears in, so don’t replace it. But that leak-ing rear evaporator has to go. And of course, remove the blower motor (FIG.3 ) and with a shop air gun, thoroughly clean carbon dust and copper particles from the blower motor assembly and the blower case, then reinstall. ■

Figure 3: Blower motor for rear system on GM full-size SUVs sheds cop-per particles as it wears in. Particles are picked up by the motor brushes and blown onto the aluminum evaporator, causing corrosion and leakage. Evaporator must be replaced, but motor and brushes may be cleaned with shop air and kept in service

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AND NOW FOR AN EVAPORATOR LEAK WE’D LIKE TO TALK ABOUT

WHAT? ANOTHER GENERAL MOTORS ANTI-FREEZE

Every engineering group of every car company wants exclusivity, and that often extends down to the small-est things. Then the corporate purchasing teams for the parts departments look them over and decide there are too many parts in the system that seem to be duplicative, and they start eliminating them.

That’s why the car companies have multiple anti-freezes at the start of new model families, and some time thereafter they’re down to a single antifreeze. GM has been using “DexCool,” a mixture of two organic acid inhibitors (2-ethylhexanoic acid and sebacic acid, plus a copper-brass inhibitor called TT (tolythriazole). This is

formulated with an orange dye.GM now has a new line of Chevrolet low cab forward

medium and heavy-duty trucks and one of the engines is a 5.2-liter diesel four-cylinder. But it’s supplied by Isuzu and that pretty much explains why there’s specifi c an-ti-freeze. Isuzu has certifi ed its engines with a formula that it tested and supplies, and describes as a “long life” formula. So GM has to use that anti-freeze, for openers anyway, until it can validate an alternative.

That anti-freeze is green as supplied, and GM warns not to use conventional American green, but a yellow dye antifreeze that is available from dealers (FIG. 4.


That green antifreeze is not the green that GM used in the early 1990’s on Saturn either—that was a low-silicate “extended life” antifreeze that was picked up from the Mercedes-Benz shelf, a rather curious selection because it contained nitrite, an addition that Mercedes found was helpful in protecting diesel engine cylinder wet liners.

So what is that antifreeze? We had it analyzed and it turns out that it’s just a single organic acid – 2-EHA plus TT. That differs from DexCool, which has the second or-ganic acid (sebacic acid), and some other antifreezes that use other ingredients, such as molybdate, along with TT.

You can get that specifi c antifreeze at dealers, although our view is you can use DexCool, as the DexCool mix has certainly proved to be compatible with 2-EHA and TT.

These new medium and heavy-duty trucks are primar-ily for “upfi tters,” who attach specifi c design bodies to them, such as for construction and garbage removal.

That green antifreeze is used only with the 5.2-l diesel, and GM has made it clear that the specifi c antifreeze is essential, however. Why you ask?

First, there is a green propylene glycol antifreeze around, and if you use that, bad news (engine damage) says GM. Second, Isuzu provides the diesel engine war-ranty for GM, and (as has happened with many engines from outside suppliers) mandates a specifi c coolant.

Also noteworthy on the new Chevy medium-to-heavy duty models, the Isuzu diesels have a fuel-to-air fuel system cooler, which is mounted in front of the rear axle (FIG. 5).

The diesel fuel cooler is intended to compensate for

higher fuel pressure and temperature (caused by changes in camshaft timing). The cooler is part of the fuel return circuit and it reduces temperature of the fuel before it goes back into the fuel tank.

Those new low cab forward chassis are Class 3 to 5 (3500, 3500 HD, 4500, 4500 HD, 4500 XD, 5500 HD and 5500 XD). The engine lineup also includes a 6.0-liter gasoline V8, 6.0 CNG/LPG-capable version and a second Isuzu four-cylinder diesel, with a displacement of 3.0 li-ters, which also gets that green antifreeze as the OE fi ll. ■

Ford once had at least four anti-freeze formulas world-wide, and is working its way down to one (a Dexcool or-ganic acids type), even though it took a lot of engineering work on the powertrain cooling systems to do that (and

dropping the 5.4-liter V8 and 6.8-liter V-10, among other things).

Fiat Chrysler’s domestic line used “conventional American green” (called “inorganic additive” technol-

Figure 5: Fuel cooler mounted in front of rear axle on low-cab-forward heavy—duty and medium-duty chassis serves to cool Isuzu diesel fuel as it fl ow back to the tank.

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Figure 4: New GM anti-freeze is just a single organic acid (2-EHA) for Isuzu diesels in low-cab-forward Chevy heavy-duty and medium-duty chassis converted for work uses by upfi tters.

OTHER ANTIFREEZES


Of course, no one (except classic vinyl collectors) has “pho-nograph” records anymore, much less broken ones. But it was a common expression for repetitiveness, and we are going to sound a bit repetitious, although with a new example. It’s the importance of being able to refl ash modules, but also to be aware that not everything is caused by corrupted software. And the diagnostics may be more tedious than you’d like (well, that’s no surprise, is it).

Some 2013-14 Chevy Malibus have been encountering instru-ment cluster issues--- HVAC and radio displays and the cluster gauges going blank, which may be accompanied by no-crank-ing, U-codes on the scan tool and airbag warning lights (traced to a blown fuse if it comes into the shop). Although possible, it’s unlikely this is a software issue. However, the motorist may re-port that the car goes months on his daily commute and there’s never a failure. However, it did occur when he and his wife were out shopping on a weekend.

You can replace the fuse and test drive the car, but the prob-lem probably won’t recur, which likely would convince you that you fi xed it by replacing the fuse. No such luck. Eventually the customer will be back with the news that the problem recurred.

Which would seem to indicate it’s some sort of intermittent. So you install still another fuse, and this time if you take the motor-ist with you on the test drive, the failure will recur. That is the clue—check the harness under the passenger’s front seat.

Figure 6: Fiat Chrysler has used three antifreezes over the years, a conventional American green to 2000, when it switched to an orange-dye “hybrid” organic acid formula -- G-05, sold in the aftermarket with yellow dye. In 2013, it switched to a purple dye organic acid formula.

Figure 7: If 2013-14 Malibu suffers IP wiring glitches, check to see if pas-senger side wiring harness (1) goes through seat frame (2). If so, it likely has been damaged, and should be re-routed and repaired.

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ogy—silicates, phosphate, borate, nitrate and other min-eral inhibitors. That was replaced in 2000-2012 by what was called a “hybrid OAT” (organic acid technology) anti-freeze, basically a low-silicate formula sold in the af-termarket as G-05—yellow dye vs. the OE orange dye. In

2013 FCA switched to purple dye organic acid antifreeze. FIG.6 Some early FCA products, primarily Fiat models, had an orange dye organic acid antifreeze but that was dropped shortly after production started, and the purple dye went across the board. ■

WE’RE SOUNDING LIKE A “BROKEN RECORD”


That’s not particularly easy, although you may be able to detect wiring harness damage by feel. More likely, you’ll have to remove the seat for an inspection. If the harness was routed through the seat frame, that can cause a short to ground, usually from the harness making contact with the seat frame, or within the harness. The fi x is to separate damaged wires, tape them over with premium electrical tape and route the harness away from the frame. You may have to unplug the wiring harness in the process. See FIGS. 7, 8, 9.

Now let’s look at what seems to be a seat heaters issue that may have a similar cause that has been occurring on a slew of GM cars, including that Chevy Malibu; 2010-15 Chevy Cama-ro, Equinox.and Terrain; 2011-15 Buick Regal and Chevy Cruze; 2012-15 Buick Verano and Chevy Sonic; and 2013-15 Malibu.

The failure of the heated seats to operate is intermittent, and there should be a communications code – U-0209 (lost commu-nication with the front seat heating control module), set in the HVAC module.

The temptation is to replace the heated seat module, (FIG.10 ) on the underside of the driver’s seat. But do not; it won’t help. If you check OE service information, you should fi nd this is a software issue, and although you can get a temporary fi x by removing then reinstalling the module fuse (K29), there is new software that really provides a durable fi x. If you don’t fi nd the U code, however, then you should go through the OE service information’s heated seat diagnostics. ■

Figure 10: Failure of heated seats on a range of late-model GM cars and SUVs may seem to be caused by heated seat module on underside of driver’s side seat, and because it’s held by just a couple of screws, it’s a tempting parts change. But it’s unlikely to be responsible.

Figure 8: Remove harness from seat frame (1), disconnecting electrical connector if necessary (2). Figure 9: Repair harness (1) with premium electrical tape and secure to seat

wiring harness (2) with tape.

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Shops seem to have heard that Denso compressors in a range of Toyota products have something called a fl ow sensor, and we’ve been asked to comment and explain.

The subject came up because when the sensor fails, techni-cians have reported, the air conditioning performance fails – warm air from the HVAC vents. They’ve discovered that this sensor is involved because there’s a trouble code—No. B1479 and the service information says it’s in the fl ow sensor circuit. The code may be stored as an active one or a history code.

There apparently were some issues with the A/C compressor on a number of Toyota products, particularly the 2012-13 Camry with the 2AR-FE—that’s the 2.5-liter in-line four-cylinder; and the 2GR-FE, which is the 3.5-liter 60-degree V6. And both those engines have that compressor with the fl ow sensor (as do other Toyota products, including the Prius). The important thing to note is that the sensor is not available as a detail part, so if it’s bad, the only fi x is to replace the compressor, on which the sen-sor is mounted.

Now let’s take a look at this sensor and its circuit.The sensor is engineered to determine the amount of refrig-

erant fl ow into the compressor, converting the fl ow to a volt-age that varies inversely and proportionally, and that voltage is transmitted to the A/C amplifi er.

As the fl ow increases, the voltage drops; as the fl ow drops, the voltage increases. It’s a fi ve-volt circuit, with the reference voltage supplied by the amplifi er, which produces a proportional signal to the engine control mod-ule (ECM) through the CAN bus (Controller Area Network). The ECM uses that signal to control engine r.p.m. while the A/C is on. If the system has an electric motor-driven com-pressor, the r.p.m. of the compressor (as with a Prius or other hybrids) is increased or de-creased as indicated. So the sensor readings serve to “tune” the compressor output to the cooling needs of the system.

How the sensor works: it’s basically a mass fl ow device that uses a spool that moves ac-cording to the amount of refrigerant fl ow (FIG. 11). There is a magnet on the spool, and the spool movement changes the magnetic fl ux, which changes the output voltage from the sensor.

That sensor should output a fl uctuating 0.7 to 3.8 volts with the blower switch on high and the system running. With the A/C and blower off, and ignition on, the voltage should be 3.8-4.2 volts. If the voltage is constant (0.7 to 4.2 V) for more than four seconds with the system turned on, that confi rms the sensor is defective.

The voltage measurements are per the Toy-ota Techstream, connected to that underdash

diagnostic link connector (“DLC3”) and using the data list for air conditioning from the body electrical menu. If you don’t have a Techstream (basically a dealer scantool), you can get a Tech-stream Lite kit, which allows your PC to run the factory soft-ware . The “Lite” features the Drew Technologies “Mongoose Pro Toyota 2,” which you can buy from the manufacturer or in a full kit from Toyota dealers. Yes, it gives you the capability to reprogram, so here’s “another broken record” recommendation from MACS Service Reports.

The B1479 code, as noted, is the defi nitive word for the fl ow sensor circuit, and if you don’t have that code, the problem with the A/C is elsewhere. The diagnostic sequence with the “Lite” is in a service bulletin, and we always assume that you have ac-cess to bulletins, and rarely repeat material from them in these pages.

Toyota also includes a harness test that requires nothing more than an ohmmeter (remember, the B1479 code is a circuit code, not a parts failure code). The harness test is made at the A/C amplifi er with the sensor wiring unplugged, and the procedure is to look either for low resistance (“below 1 ohm”, although it shouldn’t be surprising to get readings slightly higher) or 10,000 ohm or higher. Once again, the details are in a service bulletin. ■

Figure 11: Flow sensor on many Denso compressors is an effi ciency tuning device that changes engine r.p.m or compressor speed according to refrigerant fl ow. But if sensor fails, it is not avail-able as a detail part—entire compressor must be changed. Sensor operates a spool valve that changes fl ux of magnet, which provides output signal to A/C amplifi er.

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THE NEW DENSO COMPRESSORS – DISCUSSION BY POPULAR REQUEST


MACS Service Reports is published monthly by the Mobile Air Conditioning Society Worldwide. It is distributed to members of MACS Worldwide and is intended for the educational use of members of the automotive air conditioning service and repair industry. Suggestions for articles will be considered for publication, however, MACS Worldwide reserves the right to choose and edit all submissions.

Unless otherwise noted, all photos/art by author.

Editors: Elvis Hoffpauir, Steve SchaeberProduction Designer: Laina ForceyManager of Service Training: Steve Schaeber

Mobile Air Conditioning Society WorldwideP.O. Box 88, Lansdale, PA 19446Phone: (215) 631-7020 • Fax: (215) 631-7017Email: [email protected] • Website: www.macsw.org

OIL SEPARATOR

The oil separator is a key part of the newer compres-sors, and its purpose is obvious: with today’s lower oil charges, the compressor gets effective lubrication by keeping almost all of the oil in the compressor, not allow-ing it to fl ow out through the circuit with the refrigerant. That also reduces the energy required to operate the com-pressor, as even droplets of oil take power to be circulat-ed. It’s not uncommon to see oil charges of four ounces or less, and as an example, the Chevy Cruze oil fi ll (with R-134a at this writing) is just two ounces.

Here’s a look at the Denso unit in the Camry we’ve been talking about. The oil and refrigerant fl ow into the separator (FIG. 12) from the discharge chamber port into the separator. The movement of the fl ow causes the oil separator cylinder to turn, which produces centrifugal force that separates the oil and refrigerant. The refriger-ant fl ows to the condenser through the discharge port. The oil fl ows through the reservoir chamber, into the in-let, cylinder and discharge chambers, lubricating the in-ternal parts of the compressor in the process. This separa-tor does make it diffi cult to drain oil from compressors of this type, and because of the low charge, you should not expect a lot to be removable, during refrigerant recovery or when trying to remove oil to balance the charge prior to compressor replacement. The draining issue will be something you’ll encounter on many new compressors with oil separators, some more diffi cult than others. ■

REFRIGERANT BLOWS OPEN THE PRESSURE RELIEF VALVE

When a pressure relief valve starts popping off, the problem (refrigerant escape) should be reasonably straightforward to di-agnose, right? The PRV is defective, something is causing the high-side pressure to go way up, or there’s a restriction. It be-comes an issue when the technician can’t seem to fi nd the an-swer in one of these “obvious” possibilities.

The vehicle was a 2006 Ford E-450 outfi tted as an ambulance with the 6.0-liter Super Duty diesel. No, we’re not going to fi nd something weird with the engine creating the problem. And al-though the long hoses in ambulances do create a leakage issue, this case is a verifi ed loss through the PRV.

The pressures started at 30 psi low side and 325 psi high side at idle, and when the technician blipped the throttle, the high side pressures went to 500 psi (low side drops to about 20 psi), at which the PRV obvious would open. The shop already had

“replaced everything,” – the compressor (well it was leaking, so…), condenser, orifi ce tube, radiator, fan clutch assembly and the rear expansion valve. And when the throttle was blipped, the technician could verify good airfl ow through the front cool-ing module. Yes, the technician also had fl ushed all the refriger-ant lines and hoses, and even the evaporator. So what could he have missed?

The answer: getting a full vehicle history, which would have told him that a compressor previously had been installed. That compressor failure had left debris wedged in the line to the con-denser, and despite the maximum effort at fl ushing, it hadn’t budged. Use of a premium infrared thermometer should have picked up the pressure drop to the condenser, instead of having to go through a physical inspection with a rod. ■

Figure 12: Oil separator keeps most of the oil within the compressor, so oil change can be minimized for maximum effi ciency. Separator sends oil through reservoir chamber, inlet chamber, cylinder and discharge chamber. Only refrigerant (and a minimum amount of oil for circulation of any trace dye) fl ows with the refrigerant.

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MACS Service Reports Quiz #MSR032017Based on March 2017 issue of MACS Service Reports.

This test must be received within 30 days in order to be processed.Fill out the information at left, and circle the correct answer for each question in the box below.

Mail or fax your completed test to: MACS Worldwide, P.O. Box 88, Lansdale, PA 19446; Fax: (215) 631-7017

1. Two technicians are discussing a DTC which describes an issue for high voltage on the AAT (Ambient Air Temp Sensor) signal wire. The service records on the vehicle indicate the ra-diator has been replaced recently. Technician A says that the problem may be the sensor signal wire may be pinched under a radiator bracket causing the condition. Technician B says the sensor may have been left disconnected. Which technician is correct?

a. Technician A onlyb. Technician B onlyc. Both Technicians A and Bd. Neither Technician A or B

2. A negative coeffi cient thermistor’s internal resistance _____________________

a. Increases when sensed temperatures increaseb. Decreases when sensed temperatures decreasec. Remains constant but increases current when sensed temperatures decreased. Increases as sensed temperatures decrease

3. Typical OAT and AAT sensors will read __________________ volts with a voltmeter con-nected between the module’s sensor ground and the sensor’s signal wire (harness side) when the sensor is disconnected.

a. Between .2 and 4.8 voltsb. Between 2.4 and 2.6 voltsc. Steady .5 voltsd. Steady 5.0 volts

4. Two technicians are discussing a late model Cadillac’s lack of ambient temperature displayed on the center stack radio / DIC. Technician A says the M.O.S.T. data bus may have a communications problem. Technician B says there may be a problem with the sensor’s mounting bracket having a proper ground. Which technician is correct?


5. OAT / AAT sensors are used by both the PCM and HVAC / IPC for temperature inputs. True or False?

a. TRUEb. FALSE

6. When a vehicle is stopped in traffi c the OAT sensor will ________________________

a. Cool down and update the PCM and IPC with a new outside temperature readingb. Heat up and update the PCM and IPC with a new outside temperature readingc. Cool down but has its new reading delayed for update by whichever module it connects to until the vehicle begins moving again.d. Heats up but has its new reading delayed by whichever module it connects to until the vehicle begins moving again.

7. Which of the following best describes the M.O.S.T. bus control signal?

a. Goes from 5 volts to ground when the ignition is switched on to wake up the modulesb. Goes from low to high (12-volts) when ignition is switched with momentary pulses to ground from the radio to request module status on the bus.c. Has a constant pulse from 1.5 volts to 3 volts whenever the BCM is awake and the ignition is switched on.d. Contains a pair of 120 ohm termination resistors.

8. When corrosion is discovered in a splice connector for a sensor circuit, a portion of that spliced circuit should be ____________________________________________________________

a. Cleaned with hot soapy water and dried with dry shop airb. Sprayed with a water dispersant such as WD-40c. Treated with a conductivity enhancer like Stabilant 22 and taped up with electrical taped. Replaced with a new section of wiring and re-spliced with either solder and heat shrink or a crimp splice connector that has sealant in it that seals the splice effectively.

9. Two technicians are discussing an AAT / OAT sensor’s wiring. Technician A says that a voltage drop can be performed by measur-ing from one end of the sensor’s circuit to the other when the sensor is heated with a hair dryer / heat gun. Technician B says the sensor and module can both be disconnected and a power and ground source can be connected at one end and a substitute load drawing no more than the wiring size can handle connected at the other end to load the circuit properly for a dynamic voltage drop test. Which technician is correct?


10. Looking at the PID titled “Surrogate” in the M.O.S.T. bus on a scan tool can be helpful in de-termining _______________________________

a. There is no A/C request on the scan tool but the scan tool can command the compressor on and the A/C works.b. The cabin air temperature scan reading is minus 40 degrees F. Technician discovers the sensor is missing and replaces it.c. The outside air temperature sensor indicates plus 39 degrees F. when it was 95 degrees F. ambient. The sensor is defective.d. All of the above.

UH OH! YOU BROKE SOMETHING - Constant...

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