2011 04 Ms

MACS Service Reports is the official technical publication of the Mobile Air Conditioning Society Worldwide, Inc., P.O. Box 88, Lansdale, PA 19446. The material published in MACS Service Reports expresses the views of the contributors and not neces-sarily 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 informa-tion 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 2011 1 MACS Service Reports

A service to members – $70 annually to subscribers © Mobile Air Conditioning Society Worldwide

The A/C compressor doesn’t engage on a 2006 Toyota Camry, but with a jumper wire to the clutch coil, it will. Before we write much more, we’ll bet most of you are thinking: “bad clutch relay.” If ever there was a “classic”

pattern failure, this is certainly one. But the truth is that the relay was substantially rede-

signed some six years ago, and although we still hear of failed Camry relays, the failure rate seems to be not

By Paul Weissler, MACS Senior Technical Correspondent April 2011

IT’S OBVIOUS… OR IS IT?

Figure 1: 2006 Camry wiring diagram shows the wiring from the A/C amplifi er through the dual pressure switch to the clutch relay. Although bypassing the relay with a jumper to the A/C clutch coil terminal would activate the clutch, the problem was a break in the wire from the pressure switch to the relay.

ALSO INSIDE THIS ISSUE:

SO YOU SUSPECT THE RELAY ..................................................................................................................................................... 2THE HYBRID COMPRESSOR OIL ISSUE .................................................................................................................................... 3THE BATTERY AND THE BODY COMPUTER ........................................................................................................................... 6A TOUGH DIAGNOSIS (A FOLLOW-UP TO LAST MONTH’S “EVAPORATOR TEMPERATURE SENSORS—SOME THOUGHTS”) .........................................6


When the clutch doesn’t engage, or a fan doesn’t go to high speed, the relay is invariably one of the items on the list of suspects. If you have another relay on the shelf and it’s the correct one, you can do a fast substitution. But there are lots of different relays, and in general, too many parts that are likely to not be on the shelf.

A better alternative is a new relay test kit recently in-troduced by Hickok-Waekon (www.hickok-inc.com, 800-342-5080). The idea is neat and simple. The kit (Waekon No. 77465) contains four plug-in replacements for all common relay applications (Figure 2). One is a four-terminal replacement, but some of the fi ve-terminals

also may work in place of a specifi c four-terminal. The replacement is sort-of a simulator. Install the appropri-ate one in place of a relay, activate the circuit, and if the circuit that includes the coil side of the relay is good, the body of the relay simulator will glow brightly (Figure 3). If there’s high resistance somewhere in the circuit (other than the relay), the body will glow dimly. If the body doesn’t glow at all, there’s apparently a break in that circuit.

If the simulator body glows brightly, the next step is to

check the secondary side circuit, using the kit’s remote test switch (which as shown in the photo of the kit, is a push button switch with wires). Plug the terminals of those wires into sockets in the relay simulator body, and with the circuit activated, press the button on the switch, which jumpers across the terminals of what would be the secondary side of the relay (Figure 4). If the circuit now works, the relay was the problem and replacing it should be the fi x. If it doesn’t, there’s a problem elsewhere in the circuit that includes the relay secondary, and a new relay would be a waste of time and money.

There’s also a new type of relay test kit, recently intro-duced to the market by Lisle Corp., another well-known specialty tool/test equipment maker. In fact, there are two kits, each with four “jumpers.” Each jumper is a plug-in replacement for a specifi c type of relay, and the removed relay is then plugged into the top of the jumper, with which it forms a unit (Figure 5). The jumper has

Figure 3: If the coil-side circuit of the relay is good, activating the ac-cessory should make the simulator body glow brightly. If the simulator body doesn’t glow, the circuit is defective, and if it glows dimly, there is resistance elsewhere in the circuit.

Figure 2: This Waekon relay simulator kit makes it easy to test relays and the two circuits in which they are wired. It includes the four simula-tors to replace different relays and a push-button test switch.

SO YOU SUSPECT THE RELAY

much different from those of A/C clutch relays on any make.

The technician believed the pattern failure and re-placed the relay, and by now you should not be surprised to fi nd that it didn’t fi x the problem.

Aha, you might be thinking (as some technicians did), it must be the amplifi er (A/C module). Well, over the years we’ve heard of amplifi er failures, but considering the rate at which Toyotas sell, the rate is not indicative of a signifi cant pattern failure. So once more, the parts replacement wouldn’t fi x the problem. When it comes to relays, we have some additional thoughts, discussed in the following article, “SO YOU SUSPECT THE RELAY.”

What was the problem? Answer: a broken wire be-tween the relay and the dual pressure switch (Figure 1). Why do wires break? If you ask someone who does work

for body shops, like mobile technician and MACS Con-vention trainer John Anello, he’d probably say, “Collision damage is a major cause.” Technicians who work on a lot of very late models might say, “When add-on accessories are installed, the installers may yank on existing harness-es, damage existing terminals and bends pins in multi-way connectors, tap into wires with Scotchloks and then maybe move them somewhere else, leaving damaged wiring in their wake. And then there’s just the usual mis-handling from technicians doing unrelated underhood service. But we’ll tell you this: for every new car with a screw driven through a wire in a harness on the assembly line eventually causing a problem, there are probably a few hundred problems from things that happen after the car is put into service.■


contact tabs for jumper wires or multimeter leads, corre-sponding to the wiring connections of the relay that can’t

be reached with a jumper or meter lead. That permits easy testing for continuity and voltage at all terminals of the relay coil and contacts, so the technician can check for power at each, and jumper across with a conventional jumper wire to test the circuit operation.

The primary kit, No. 56810, contains four relay jump-ers, a red one for 1984-96 Ford, a blue for later Fords and Chrysler products, a green for General Motors, Navistar truck and Kia, and a yellow for that common Bosch type used on most cars since the 1980’s. The second kit, No. 60610 (Figure 6), has an orange relay for GM and Navi-star, a white for Honda, Toyota, Nissan and 2009 Hyun-dai, an orange for certain GM and Navistar, and a purple for Nissan fuel pumps to 2004, and 2009 Hyundai. The purple may not be particularly useful, but the kit other-wise has important coverage. ■

Figure 4: If the relay simulator glows brightly, the next step is to check the secondary side circuit with the test switch with two wire leads, so it actually forms a type of jumper wire. Just plug each wire terminal into one of the special sockets in the relay simulator, then press the test switch button. If the circuit now works, the relay is defective. If it doesn’t, the problem is elsewhere in the circuit and a new relay won’t help.

Figure 5: Lisle “jumper” replaces the relay in the fuse box cavity, and the relay itself plugs into the top of the jumper to complete the test setup. The jumper has accessible contact pads and tabs for circuit and relay testing with jumper wires and a multimeter.

Figure 6: This is one of the two kits of four Lisle “jumpers” that plug into the fuse box relay cavity.

THE HYBRID COMPRESSOR OIL ISSUE

If you’re a regular MACS Service Report reader, you know we’ve covered the subject of the effect of PAG oil contamination of A/C systems with electric drive compressors. We have explained that the on-board di-agnostics will check the ground isolation of the system and log a diagnostic trouble code if the resistance is low – something like the ground fault interrupter switch in many household circuits. One of the possible causes of that code is PAG oil in the system, instead of the specifi ed polyol ester (POE) oil, causing loss of resistivity in the chambers of the compressor.

However, there seems to be an impression that if the hybrid system turns on a ready light, all is okay, and if the car arrived at your shop without a warning , there is

no oil contamination problem with the A/C, even if the A/C hadn’t been on.

There are two things wrong with this theory, certainly on Toyota systems like the Prius, which are the bulk of the hybrid market with electric motor-drive compres-sors at this time. First, the oil issue (assuming only par-tial contamination and not a totally incorrect charge with PAG oil) that causes a trouble code to be logged, occurs only in the fi rst seconds of A/C operation. If the CAN (controller area network) data bus diagnostics detect the low resistivity, it may log POAG-611, and this can disable the A/C, but it does not prevent the vehicle itself from running. Neither Toyota nor DENSO, the manufacturer of the system, discloses the computer algorithm that sets


that code. So if the A/C doesn’t run, the fi rst thing to do is a trou-

ble code scan, and if that code comes up, check vehicle history for any A/C service, to determine if there’s any chance that the system was recharged and PAG oil added instead of polyol ester oil (POE) -- ND-11 recommended by Toyota for the DENSO system. If you trace the prob-lem to signifi cant oil contamination (Honda says any contamination), you probably have heard that the manu-facturers say to replace all the components, and that is really, really expensive.

However, you should be aware that in addition to contaminated oil, the code could be caused by other is-sues, such as a defective electric motor in the compressor or a communications problem in the CAN itself, and a scan tool with OE-level diagnostics also may produce a CAN communication trouble code. But if the only code is POAG-611, a good vehicle history can give you the start-ing point, and if POE oil contaminated by PAG is strongly indicated, keep that in mind. But note that a basic check of the electric motor-drive is not diffi cult, and a defec-tive motor, which certainly could have been caused by oil contamination (if it occurred some time ago), is impor-tant to also keep in the diagnostic evaluation.

It is possible, although unlikely, for the A/C to log both

a CAN communication failure and an A/C failure from PAG oil contamination.

Compressor Motor Testing If you don’t know whether there is severe oil cross-

contamination causing the motor to fail, a good way to start is by checking the compressor motor for a short to ground. This is Toyota’s recommended procedure:

• Clear the trouble code(s) and turn the power switch (“ignition”) on.• Set the blower speed to High, the Temper-ature to MAX COLD and the A/C on.• After three minutes, turn the switch off and remove the high-voltage safety plug from the battery box cover.• Disconnect the two-wire connector from the high-voltage compressor and connect a grounded ohmmeter to each of the two ter-minals on the motor. Each should read ultra-high resistance (2 megohm or greater). Note the wiring schematic, which shows the eight wires that connect to the compressor. You want the two that go to the inverter. See Fig-ures 7 and 8.• If the readings are low, this indicates a

shorted motor. Replace the com-pressor assembly. If you get the acceptable readings (over 2 megohm resistance), try to oper-ate the A/C system but without a cooling load, this way:

A/C Cycle Test • Reinstall the connector to the compressor motor and refi t the high-voltage safety plug. • Clear any trouble codes and turn on the power switch (“ignition”).• Set blower speed to LOW, Temperature to 77 degrees F. and A/C (or defrost) on.• Run the A/C for 10 min-utes, which will collect a maxi-mum amount of oil in the com-pressor.• Turn the power switch off and let the system sit overnight.• Remove the high-voltage safety plug and repeat the test with the two-wire connector un-plugged from the high-voltage compressor (grounded ohmme-ter to each of the two terminals on the motor.• Once more you should get

an ultra-high resistance reading Figure 7: Wiring schematic for the electric-motor-drive compressor in a 2010 Toyota Prius. The two-wire connector is for those at the bottom, which run to the inverter.


(for this test, Toyota specifi es 3 megohm or greater).

If you get signifi cantly lower readings (be sure to check ohmmeter and connections to be sure), replace the com-pressor. If however, you have evidence that a PAG oil has been in the system, Toyota does recommend changing all the components in the A/C system.

Oil Contamination If you’re able to absolutely confi rm that a Toyota elec-

tric-drive compressor system was charged with PAG oil (such as with a vehicle history), do you really want to replace all the components? Well, better to ask, does the vehicle owner want you to do that? Almost surely not, and so long as the owner fully understands—and accepts the cost of the effort-- you do have the option of trying to remove as much oil as possible and recharge the sys-tem using the correct (ND-11 or equivalent) POE oil. The worst that can happen is that the effort doesn’t succeed, and then the vehicle’s owner can decide if he wants to make the investment in new parts.

Toyota does recognize that a small amount (undefi ned) of PAG oil may have been put into the system, causing the trouble code to log. So it suggests collecting the maxi-mum amount of oil in the compressor, then draining the compressor and adding fresh ND-11 oil. This could well

lower the oil contamination ratio suffi ciently for the sys-tem to function normally.

What would be “signifi cant oil contamination?” Toyota doesn’t say, but the Prius system takes only 3.5 oz. of oil because the compressor itself is designed with baffl es to minimize oil circulation with the refrigerant, keeping most of it in the compressor, both to improve lubrication and reduce energy used by the compressor to circulate it. So “a couple of ounces” is not minor stuff. However, as noted, Toyota does allow for the possibility of eliminat-ing the problem without replacing all the parts, so you’re not way out in left fi eld.

If you try to clear the codes, but POAG-611 comes back and the system will not operate, use a recovery/recycle/recharge machine. Then replace what oil you recover with pure ND-11 POE oil. Clear the code once more, and if the A/C is operative again, happy days.

If you don’t remove any or enough oil with the R/R/R machine to clear the code, or perhaps you’d prefer an ap-proach that is more likely to remove a maximum amount of contaminated oil, you can proceed this way:

Perform the A/C cycle test for 10 minutes to collect oil in the compressor, turn off the power switch and remove the high-voltage safety plug from the battery cover. Then remove and drain the compressor. As we’ve noted, the Prius electric-drive compressor is designed to trap a lot of oil, so it is possible you may be able to get much of it out this way. It probably won’t be a quick and easy drain, but from the vehicle owner’s standpoint it beats replacing expensive parts. It is possible that the compressor won’t run (and the code to be cleared), but then, there still may be enough oil collected in the compressor for a drain to work.

If you have a case of major oil contamination, an in-operative system as a result and no fi x from the previ-ous suggestions, we’re back to the possibility of fl ushing, which although not recommended by Toyota, is some-thing the motorist may prefer as an alternative to replac-ing all the parts.

However, you’ll have to explain to the motorist that the fl ush also may not cure the problem, and remember, the cross-contamination limit specifi cation is just 1% for DENSO systems used by Toyota, just 2% for the Mitsubi-shi compressors used by Ford. Although DENSO does set that limit, we cannot tell you at what voltage indica-tion the code sets, or for that matter, if that relates to a specifi c oil contamination level. The chances are there’s a test or maybe more than one that the computer makes and a voltage limit that it looks for. The number may include a deterioration factor for the insulation on the electric drive compressor motor windings. Whatever the exact algorithm, there’s probably is a giant safety factor for the possibility of a technician not using lineman’s in-sulated gloves touching the compressor the instant the A/C is turned on.

Although refrigerant fl ushing removes oil, there pres-ently is no data on how effective it may be in removing

Figure 8: Illustration of compressor shows location of the motor termi-nals. Each should produce ultra-high resistance with an ohmmeter test to ground.


The once simple act of disconnecting the battery can now cause all kinds of issues, including the loss of computer memory, the triggering of antitheft codes in the radio, the setting of data bus communications codes, etc. So if you don’t have a computer memory saver, you could face this problem. Then, what if you have one, but it plugs into the cigarette lighter (which typically is part of the dashboard), and you have to pull the dash for a job, such as a heater core or evapo-rator replacement?

Outwardly, there seems to be not much choice for saving the radio and computer memories, if all you have is that simple computer memory saver. You cer-tainly do have to disconnect the battery – after get-ting the radio antitheft code from the motorist (if the antitheft is activated). And if it takes some doing on his/her part to locate the code, so be it. Otherwise, if you disconnect and the audio system and it locks up, you or the customer probably will have to go through the dealer to get a factory-programmed code to reset the system. Fortunately, many late-model GM cars just automatically sense the VIN, so if the audio system hasn’t been changed, it should reactivate. But never assume the car you’re working on will reinitial-ize. Check the owner’s manual if the motorist doesn’t know.

If you just remove the dashboard without discon-necting the battery, surely the instrument cluster com-puter, and likely the body computer if part of the dash assembly, will continue to be powered until the ve-hicle electronics suddenly lose the ground provided through the dashboard. That loss of ground may cause an internal body computer spike that could blow ei-ther or both modules (and any others that might be grounded through the dash). Whereas if you first just disconnect the battery, the entire car will lose power (and all the computer modules will be electronically

safe). But then, except for some safety systems and the

Figure 9: The computer memory saver is an essential special tool. But when you’re working under the dash and may have it out and apart for a while, you need more than a saver with a 9-volt battery. And you certainly want some place other than the cigarette lighter socket to plug it in for power, if the socket is in the dashboard. This EZ-Red unit plugs into the OBD II connector, and includes both a battery and a power cord for lengthy operation.

THE BATTERY AND THE BODY COMPUTER

enough contaminated oil to be successful. And a refrig-erant fl ush is not some super-fast procedure, although much of it may be done automatically, without a techni-cian in attendance. A solvent fl ush is another alternative, although it has been used primarily for removing debris and dirty oil. One system, Hecat, reports success for re-moving debris and dirty oil from condensers, evapora-tors and hoses after a compressor failure. However, it must be performed very precisely to both work and not leave any more than the slightest residual trace of the sol-vent. And here again, there is no lab data for using a sol-vent fl ush to correct a problem of PAG oil contamination of a hybrid system.

With all these facts in mind, you should carefully ex-plain the situation to the motorist, so he doesn’t expect an assured positive result. And because the compressor is designed to trap oil, we’d be inclined at this time to stop with a compressor drain. All we can say at this point is that if we get any data – lab tests or even in-depth case histories of successful fl ushes (with refrigerant or sol-vent), we’ll report them to MACS members. All that said, there have been a few technicians’ online reports of fl ush-ing after replacement of a failed Prius compressor, but no details and following the compressor replacement, no long-time performance and durability data. ■


A TOUGH DIAGNOSIS (A FOLLOW-UP TO LAST MONTH’S “EVAPORATOR TEMPERATURE SENSORS—SOME THOUGHTS”)

The 2003 Lincoln Town Car came in with a no-cooling complaint. The technician jumpered the clutch relay and the system worked, so he replaced the relay. But that didn’t fi x the problem and he noticed the compressor was noisy and the high side readings were bouncing. So he replaced the compressor (and accumulator), and al-though the pressure readings then were okay, there was obviously still a circuit problem that had to be resolved.

He ran a scan that produced enhanced Ford power-train trouble code P1462, which is for the A/C high-side

pressure switch circuit. He went through the Ford pin-point diagnostics, but found nothing wrong. However, the system would repeatedly come on intermittently for a few seconds, then cut out. He replaced the high-side pressure “switch” (a pressure transducer), but that didn’t help.

He didn’t know where to go from there, because he saw no other possibility in the wiring diagram (Figure 10). He asked for help, and then someone who knew something about the Town Car of that vintage, said it

Figure 10: 2003 Lincoln Town Car diagram in factory website shows both evaporator sensor (circled, bottom) and low refrigerant charge protection switch (circled, upper center). However, the evaporator sensor and its connection to the Powertrain Control Module did not appear in an early wiring diagram that is used in an aftermarket service information system. Even this particular factory website diagram, however, does not show the high-side transducer.

odometer, which have capacitive back-up electrical power, you’ll also have all sorts of trouble codes to erase, possibly some module initialization issues, etc., issues from loss of memory.

Better Way To Retain MemorySure, you have that little computer memory saver

that holds a 9-volt battery, and if all you’re doing is changing a battery or other quick job, and you use a fresh 9-volter, it’s fine, eliminating the worry about loss of data (although recording the radio antitheft code still is something very worthwhile doing).

But when you’re doing something significant to the air conditioning system, the job can take a day or more. There are memory savers with lantern batter-

ies, etc., but many of them just plug into the cigarette lighter socket, the same way as the 9-volter. And how often is the lighter socket not working, leaving you with a problem just as you’re starting the job? The savers that connect somewhere else, such as directly to the battery cables, and have some form of power backup are what you should have. And over the years we’ve talked about a few.

A new saver from E-Z Red, the MS4000 (www.ezred.com, 800-522-7947) is an alternative. It plugs into the OBD II connector under the dash, so it saves all the memory and presets (including the antitheft codes). It has an internal five amp-hour battery and an external charger, simple off-on switch, low-volt indicator that comes on at 11.7 volts (Figure 9). ■


MACS Service Reports is published monthly by the Mobile Air Conditioning Soci-ety 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.Nonmembers wishing to receive MACS Service Reports should contact the na-tional office. Non-member price for 12 issues is $70.

Editors: Elvis Hoffpauir, Paul DeGuiseppiProduction Designer: Laina CaseyManager of Service Training: Paul DeGuiseppi

Mobile Air Conditioning Society WorldwideP.O. Box 88, Lansdale, PA 19446

Phone: (215) 631-7020 • Fax: (215) 631-7017Email: [email protected] • Website: www.macsw.org

had been changed from 2002, to include an evaporator temperature sensor. The technician checked his wiring diagram, and it didn’t show this sensor, but the sensor was there in the evaporator, and replacing it fixed the problem.

What happened? The answer is that the wiring dia-gram in the aftermarket service information system was an early factory diagram that was in error. The di-agram on the factory website (www.motorcraftservice.com) was not perfect either. It shows the evap sensor and the low-pressure/low refrigerant cutout switch, but not the high side pressure transducer – you have to go to another diagram to see that (Figure 11).

If you go back to the 2002 Town Car, the cycling was controlled by the cycling clutch switch on the accu-mulator (closes at 28 psi, opens at 44.5 psi). The high-pressure side has a cutout switch, not a transducer, to signal the powertrain control module to break the clutch circuit if pressures reach 420 psi (switch closes

again at 250 psi to restore compressor operation). Although there are trouble codes for switch and sen-

sor failures, you basically have to go through all the diagrams and component listings to see what’s in the system, and check everything out.

That’s a lesson that’s tough to learn. All we can sug-gest is that when you have an apparently insoluble problem, certainly an electrical one, a visit to the fac-tory website might give you later information and corrected diagrams. We can remember when errone-ous wiring diagrams, with missing circuits, could take years to correct – if ever. These days, with online information, the corrections get made, if the factory has enough people working to upgrade the website. We send in correction notices, but we have seen some slow responses – one took over a year for the change to be made, and that was with a factory site. It’s a tough business, so just accept the fact that an occa-sional struggle is par for the course. ■

Figure 11: It’s necessary to fi nd this additional wiring diagram for the 2003 Lincoln Town Car to see the circuit that includes the high-side transducer (circled) and its wiring to the Powertrain Control Module.

1. When performing diagnostics, “sub-stituting with a known good part” isunderstandable EXCEPT for when:

a. The part is a high-failure item.b. There is an applicable servicebulletin.c. The part is relatively inexpen-sive.d. The part is easy to replace.

2. On a 2001 Hyundai Santa Fe:a. The A/C system’s triple pres-sure switch “low” and “high” con-tacts are wired in series.b. The A/C system’s triple pres-sure switch “low” contacts closeat pressures of about 30 psi andunder.c. The A/C system’s triple pres-sure switch “high” contacts closeat pressures of about 385 psiand higher.d. All of the above.

3. Technician A says if it detects a hardfailure of the ambient temperature sen-sor, the A/C system on a 2001 HyundaiSanta Fe inserts a fail-safe value of 25degrees C (77 degrees F.). TechnicianB says if it detects a hard failure of thein-car temperature sensor, the A/Csystem on a 2001 Hyundai Santa Feinserts a fail-safe value of 20 degreesC (68 degrees F.). Who is right?

a. Technician A.b. Technician B.c. Both.d. Neither.

4. Technician A says to initiate ATCsystem self diagnostics on a 2001Hyundai Sana Fe, press the AMB(ambient) switch at least five timeswithin two seconds while pressing theAUTO switch. Technician B says an

indication the system has successfullygone into self-diagnostics is that thedigital display will flash three times inquick succession, then display two-digit trouble codes (if any are present).Who is right?


5. Technician A says the de-iceswitch is a form of evaporator temper-ature sensor intended to prevent evap-orator icing. Technician B says that ifthe switch sticks closed, the compres-sor clutch probably will not engage.Who is right?


6. Technician A says the evaporatortemperature sensor is used on sys-tems with an expansion valve.Technician B says the evaporator tem-perature sensor is never used with anorifice tube/accumulator system. Whois right?


7. Technician A says that the evapo-rator temperature sensor should be atight fit between the fins. Technician Bsays sensor looseness, however, is anissue only if there is evaporator sur-face corrosion, and the sensor shouldnot be relocated otherwise. Who isright?

a. Technician A.b. Technician B.

c. Both. d. Neither.

8. An airstream sensor, used insteadof the conventional evaporator tem-perature sensor, is located:

a. In the plenum just before theevaporator core.b. In the plenum close to theevaporator outlet face.c. In the air duct to the A/C cen-ter registers.d. Either a or b is correct,depending on system design.

9. Technician A says the airstreamtype evaporator temperature sensoron General Motors Cadillac DTS andBuick Lucerne is removed by takingout the HVAC case, taking it apart anddepressing sensor retaining tangsaccessible on the inside. Technician Bsays that for replacement, a failedairstream type sensor on DTS andLucerne must be detached from theharness with a special tool. Who isright?


10. A periodically-seen cause of inter-mittent operation with some conven-tional evaporator temperature sensorsis when the sensor:

a. Must issue rapid changes intemperature detection.b. Sees no changes for anextended period, and goesthrough a “drift” as a result.c. Is coated with moisture, asmay happen with high humidity.d. All of the above.

MACS Service Reports Quiz #MSR0311Based on March 2011 issue of MACS Service Reports

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