F or so long and so often, you’ve heard R-12supplies are running out, you’ve probablystopped believing it ever will happen. EPAofficials at the Mobile Air Conditioning Society(MACS) 2000 convention don’t blame you, butthey say they have hard numbers now and suggestthis summer will be the last with enough R-12. The total supply may be so close that all bets willbe off late in the season, especially if this summeris a scorcher.

The EPA’s numbers: 25 million pounds are available now, and 19 million will be neededthrough this season, leaving six million for 2001(when EPA predicts 15 million will be needed). So should you retrofit any good candidate now? If you’re replacing a compressor, the new pumpwas built for R-134a, so why not? Well, becausenothing ever is that simple. The joker in this deckcould be the condenser.

At low speeds and in very hot weather, R-134adoesn’t perform as well as R-12. So this raises thenext critical question: Are you in a location wherethe A/C could be under a cooling load that couldresult in a dissatisfied customer? If so, that oftenmakes it worthwhile to stick with R-12, unless …unless you also install a new condenser — and notjust any condenser that fits, either. See Figures 1-4.

Condenser Designs There are four mass-production condenser

designs, three of them are ‘more efficient’ than thefirst and earliest. The long-produced 3/8-inch tube-and-fin condenser is a perfectly good design, rea-sonably priced and used for a long time in R-12 sys-tems. But size for size, it can’t condense as muchrefrigerant gas to liquid as any of the newer designs.And with the higher pressures of R-134a, thatbecomes a cooling performance difference.Consequently, the 3/8-inch condenser has fewremaining applications in R-134a systems.

You can find the 3/8-inch round tube condenseras a replacement. But never use it to replace any ofthe following later-design condensers:

• 6 mm round tube-and-fin (smaller diametertubes, more densely packed to transfer more heatin less space), and with an improved refrigerantflow pattern,

• serpentine (snake- or wave-like tubing patternfrom inlet to outlet, typically several flow pathswithin that tube),

• parallel multipath (a series of oval tubes with parallel flow paths, each oval tube withmore than nine passages in the superhigh-efficiency designs).

8 July 2000

Up TheHeat

Turn

Summer 2000A/C Report

9July 2000

Condenser design seems to be the most criticalfor ‘underbody breathers,’ cars with theradiator/condenser air inlets below the bumper,drawing cooling ram air from just above the pave-ment. Among imports, Honda Accords with R-134a systems long have used high-performance,parallel-flow multipath condensers, and nothingless will work. Today, you can get aftermarketreplacements in reputable name brands. MostToyotas needing a replacement condenser willrequire the equal of their original condenser, someof which are high-performance serpentines.

Unfortunately, these high-efficiency condensersare more expensive, so replacing a 3/8-inch tube-and-fin condenser with one of these could add hundreds to your retrofit bill. If the compressorfailed and has to be replaced, too, this could makethe job a very tough sell. When a compressor fails,the scattered debris often restricts flow through thecondenser. A 3/8-inch condenser has large openings and a simple flow path, so you can oftenflush out failed compressor debris.

The more efficient condensers typically have verytiny flow passages to achieve a higher surface-to-volume ratio and thus improved heat-transfer. Aftera compressor failure, they often plug with debrisand defy all attempts to flush (see Figure 3). In fact,there’s no way you can tell how successful (orunsuccessful) flushing has been on a car, until youput the system back in service. Installation of an in-line filter on the high-pressure side is the only wayto catch debris residue. This keeps debris from cir-culating through the system and causing restric-tions or a repeated compressor failure. Finding asuitable location, however, isn’t always possible.Few imports have orifice-tube systems, but on thosethat do, inspect the orifice tube for compressordebris, and replace it if necessary.

Given all of these potential problems, are you bet-ter off just flushing a 3/8-inch condenser and re-using it for retrofit? As with many automotive A/Cproblems, there are no perfect answers.

If your customer simply wants moderate coolingand can tolerate the limits of R-134a in an older-design condenser even when the weather is torrid, a basic retrofit can serve his interests ‘enhancements,’ such as an auxiliary pusher fan,can be left to a later ‘let’s-see’). Just do the job‘by the numbers’ so it holds up.

Retrofit ‘By the Numbers’1. Check the manufacturer’s recommendations

for retrofit. They should be in yourCD-ROM service information system. Or get aretrofit manual from MACS (215-679-2220).You might find the system you’re servicingrequires some special seals or other parts.

Figure 1: Cutaway of 6 mm tube-and-fin condenser.The tubes are round, and because they’re narrowerthan the previous 3/8-inch tube-and-fin, more fit into asmaller package. Because of that and other design fea-tures, this condenser is a more efficient heat exchanger.

Figure 3: There are 19 paths in the flat-oval tubing of this parallel-flow multipath condenser, a veryhigh-efficiency design. Of course, the paths are sotiny that if the condenser plugs with debris fromcompressor failure, it’s impossible to flush.

Figure 2: Serpentine condenser is made from a flatoval tube, usually with multiple passages. The tubingsnakes horizontally as shown, from inlet to outlet andwith heat-transfer fins in between. Flat oval tubing ofthe serpentine condenser is cut away in the photo,showing this one has five passages across each tube.

round tubes

flat oval refrigerant tube

louvered air fin

Examples: Nippondenso compressors normallyrequire new O-ring seals. Sanden compressors forEuropean cars may require new shaft seals. And you can forget about retrofitting vehiclesequipped with Panasonic (rotary) or Keihin (piston) compressors.

2. Draw a deep vacuum, allowing the system to out-gas any refrigerant and any moisture. If the systemwon’t pull down to 28 inches and hold for a fewminutes with the pump off, find and fix the leak.R-134a may be less expensive than R-12, but thatdoesn’t mean a leaking system is acceptable.

3. Replace the accumulator or receiver-dryer withone using XH-7 or XH-9 desiccant. There areno options on this one, since that R-12 systemmust now be at least six years old. Recharge thesystem with the specified amount of R-134a,typically 85 percent of the original R-12charge. Charge accurately, as discussed in this report. Don’t add extra refrigerant to com-pensate for a small leak. Instead, find and fixthe leak.

4. Use the PAG (poly alkylene glycol) oil recom-mended by the compressor supplier Everycompressor supplier that ships ‘dry’ compres-sors recommends a PAG oil and will void the warranty if you use a polyol ester (POE) oil instead (and that difference can be identified easily).

5. Install a high-pressure cutout switch if the vehicle came without one. Again, this is not anoption; it’s the law. If the old compressor stillis usable, your best choice is a switch that cutsout at 400 psi. or lower (to protect the com-pressor clutch) and cuts back in about 280-300psi. (so there’s some cooling without a longdelay). Japanese compressors in R-12 systemsoften use a ‘melting-bolt’ pressure-relief valve,and if this opens, it can’t reset (Figure 5).You’ll have to replace it. Install the cutoutswitch with a fitting on a service valve or with a saddle fitting on the liquid line, both of which you can get from all the major A/Cservice parts distributors.

6. Pay attention to details. Fit plastic foam stripsinto front-end gaps around the condenser andradiator, around the headlamps, etc., so all theair must pass through these heat exchangersand none can pass around them. If there’s a fanshroud, make sure it fits properly. On systemswith an accumulator, wrap it with insulation(household foil-backed foam tape works).Secure refrigerant lines to their brackets,adding any brackets necessary to shield thelines from the exhaust or other hot surfaces ofthe engine.

7. Check the fan operation. A fan clutch that slipsor an electric fan that comes on late will raisesystem pressures, reducing cooling.

8. Don’t forget an R-134a-retrofit label to go withthe new fittings. And be sure to put a new retro-fitting on both service valves, not just the oneyou use to charge the system.

6. If you’re replacing a compressor that failed,explain your condenser decision to thecustomer, too.

Replacement CondensersThe condenser, part of the car’s crush-zone, is one

of the first parts to go in a front-end collision. Boththe motorist and the insurance company will putthe pressure on to do the repair for less. Savingmoney by installing a 3/8-inch tube-and-fin replace-ment condenser is tempting. But that solution maymean a 25-percent reduction in cooling capacity(maybe even lower capacity than that).

How to tell a good replacement condenser? It’s notsimple. Sticking with the major brands and pickingthe recommended replacement type are your bestbets. The big companies (and most smaller suppli-ers) just won’t list a woefully inadequate condenser.

10 July 2000

Turn Up the Heat

Figure 4: Cutaway of an ovaltube parallel-flow multipathcondenser. Baffles in the end manifolds produce the flow paths.

Figure 5: Japanese R-12 compressors typically have‘melting-bolt’ pressure-reliefvalves. High pressure pro-duces high refrigerant tem-perature, melting the specialsolder in the bolt and ventingthe refrigerant into the atmos-phere. Because this reliefvalve cannot ‘reset,’ you mustreplace it if it opens.

baffle

manifold

flat oval tubes

bolt

melt metal (special solder)

However, even among the 6 mm serpentine and par-allel-flow multipath designs, there’s significantvariation in design and manufacturing quality andtherefore, in performance.

The details are still being worked out, so nothingis for sure in the following:

The real answer is a heat-exchanger rating system,and MACS supports a program to produce ratings forall automotive heat exchangers. The PerformanceReview Institute, an affiliate of the SAE (Society ofAutomotive Engineers) in cooperation with commit-tees of industry technical specialists, has been askedto help produce and then administer the program. If itgoes into effect, each condenser from a participatingmanufacturer would be compared with the originalequipment specification part, for heat-exchangecapacity, for fit and for durability.

Charge Accuracy Today’s R-134a systems take as little as 16-18

ounces of refrigerant. The systems are leak-tight,and the low capacities leave little margin for error,low or high. A 10-percent margin still is the rule ofthumb for charge accuracy. However, on late mod-els that translates into 2-3 ounces, not the 6-8ounces of older systems with their 3 to 4-1/2 lb.capacities and their giant receivers (handy reser-voirs because the old systems leaked a lot).

So did every shop that invested in charging equip-ment that promised ‘0.1 lb.-pinpoint accuracy via digi-tal scales and electronically-controlled solenoid valvesactually get that accuracy? The short answer is “no.”

Folks, there’s a big difference between a machine’scapacity to display a resolution of 0.1 lb. (1.6 ounces)and its capacity to meter refrigerant into an A/C sys-tem with such precision. In the early ‘90’s, GeneralMotors had its dealers buy then-state-of-the-artmachines, and GM soon found these machines typically delivered refrigerant with 15-20 percentvariation in charge volume — on three-lb. systems.With system-capacities coming down, the chargevariation percentages would go up, and that was a disaster in the making. Too much refrigerant raises pressures and causes noise; too little affectslubrication and causes noise; either reduces cooling.

New MachinesA/C performance after service wasn’t good in too

many cases, and perfectly good compressors werebeing replaced unnecessarily. So GM and Delphi (itsformer parts division) teamed up with equipmentmanufacturers to develop a new generation ofmachines that not only recovered, recycled andrecharged a lot faster, but also did so more accurately.

The so-called “Y2K technology” was promotedamong all the equipment manufacturers, not justthose who competed for the GM contract (Figure 6).So if you look at what’s new, you’ll find Y2K technol-ogy widely available and at a modest premium overthe older models. The Y2K technology machines havemicroprocessors that not only calculate the amount ofliquid refrigerant left in the line during a high-sidecharge, but may pull it back into the machine after therecharge is complete. If you want to use longer orshorter hoses, the machine can be reprogrammed tocompensate. These features can overcome charge-variance inaccuracies, which may occur if differenttechnicians use different recharge techniques.

The refrigerant scales are an improved, higher-accu-racy design whose calibration can be confirmed in theshop — no more excuses. There’s a new built-inrefrigerant identifier that’s more robust, so it won’t diefrom a few drops of refrigeration oil. If you alreadyhave a hand-held identifier that can read percentageof air in the system, you can hold off on this purchase.

12 July 2000

Turn Up the Heat

Figure 6: This recovery/recycle/recharging A/C serviceequipment is what GM dealersmust use for all A/C warrantywork. It’s electronically-con-trolled and designed forextreme accuracy in systemcharging. Although it includesa lot of features designed forGM dealers (including ahumidity gauge to tie in to GMdiagnostics), it’s also led theindustry to produce machinesthat work faster, charge moreaccurately and require lessmaintenance. Machines areavailable to the aftermarketthis year reflecting improve-ments spurred by the GMdevelopment program.

Figure 7: A clean machine isless likely to ingest dirt throughthe air intakes for its compres-sor (shown) and vacuum pump,and a clean machine performsbetter. So cover you’re A/Cmachine when it’s not in use.

Figure 8: The refriger-ant tank should fitsquarely on the scale. In this case, there’s araised retaining ring.

13July 2000

Your Old MachineWant to get more use from your

current A/C machine before youbuy a new one? Then don’t keeppressing the CONTINUE button(or bypass whatever tells you tochange the filter), but maintainyour machine. The simplest kindof all: Keep it clean and coveredwhen you’re not using it, so dirtdoesn’t accumulate and then getsucked in through the air intakes(Figure 7). Change your filters.Change the vacuum pump oil aftereach 10-15 hours of operation, sothe pump can consistently pull a

deep vacuum, and you don’t chaseimaginary refrigerant leaks (thenew GM-dealership machine hasan oil-less vacuum pump to elimi-nate this maintenance, but thisapproach has both pros and cons).Mount your tank squarely on the

scale so your reading is accurate(Figures 8, 9), and call the equip-ment manufacturer to learn howto recalibrate it in your shop (oftenthere is such a method, even if itisn’t published in the operatingmanual).

Figure 9: This tank was simply placed onthe scale, but not in the retaining ring.The tank is tilted against the side and the scale cannot register accurately, socharging weight may be incorrect.

Figure 10: An R-12/R-134a-compatibleconventional leak detector that meets themost recent leak detection standards isan acceptable substitute to find refriger-ant leaks when trace dyes are not permit-ted by the manufacturer.

Tracing LeaksNissan explained at the ’99 MACS convention

that its own dealer techs had trouble tracing refrig-erant leaks and that Japanese techs did even worsethan their U.S. counterparts. With trace dye in thesystem, however, both Japanese and U.S. techsfound about 90 percent of the leaks, so Nissanapproved a trace-dye kit. This year, Nissan techexecutives said trace dye was installed in vehicleson the production line. Nissan started on Japanese-built models last August and on U.S.-built vehiclesthis January. If the system contains dye, the under-hood refrigerant label color is green (instead ofblue), and there’s a green dot on the top of thereceiver/dryer.

Toyota’s U.S. tech people concede they would liketo see a trace dye approved, but the hangups are inJapan, where the engineering work must be complet-ed. And that hasn’t happened yet. Until then, use anup-to-date conventional leak detector (Figure 10).

Hose CollapseAn Import Service reader reported this problem in

the April 2000 issue, and it also was covered at theMACS convention. Today’s barrier hoses have amulti-layer construction, and with the manufactur-ers tweaking the designs to increase hose flexibility,it wasn’t surprising to find the innermost tube(through which the refrigerant flows) separatingfrom the next layer.

The Toyota Camry and Lexus ES300 are the first carmodels on which the problems surfaced, but we’ll betthey won’t be the last. When the problem occurs in asuction-side hose (as it did in our reader’s case), thatdelaminated hose section forms a restriction. Suction-side pressures go up, and high-side pressures hold ordrop somewhat (depending on operating conditions).The pressures on both sides often end up close to eachother, so it looks like a classic case of a bad compres-sor. A lot of compressors have been replaced unnec-essarily as a result.

Just remember also that the suction side can forma restriction, even without an accumulator. In addi-tion to internal hose collapse, there’s a suction-sidepressure regulator on Lexus LS and SC models. TheNissan Maxima/Infiniti I30 with R-12 systems had asuction-throttling valve, which performed a similarfunction. If one of these fails high, it also mimics acompressor problem (Figure 11).

One MACS member flushed a suction hose andsaw no evidence of a restriction. But the high pres-sure of the flush probably just flexed the innermostlayer out, because once he cut the hose open, hefound it permanently deformed inward.

Belt Lock Controller FailuresThey may not happen often, but as Toyota and

Mitsubishi tech trainers told the MACS convention,Belt Lock Controller failures often are misdiagnosed.The BLC is commonly used on Japanese cars with anaccessory belt shared by the A/C compressor andsuch critical components as the water pump, alterna-tor and power steering. It’s supposed to sense beltslippage and, at a certain slip threshold, open theA/C clutch electrical circuit so the other more criticalcomponents continue to function.

14 July 2000

Turn Up the Heat

Figure 11: This A/C diagnostic diagram has reinforced the ideaamong many techs that if the suction-side reading is high andthe high-side pressure is low, the compressor is bad. However, asuction-side restriction can produce the same readings.

Figure 12: The belt lock con-troller is a separate electronicmodule as shown, or it may bepart of the A/C module(“amplifier”) on Japanese carswhere the A/C compressorshares a drive belt with otheraccessories.

Figure 13: The com-pressor rpm sensoris at front of com-pressor, as shownon the inboard side.Remove compressorfor access andreplacement.

Abnormal Indications1. high suction reading2. low head pressure3. cooling insufficient

15July 2000

The BLC is an electronic mod-ule under the dash – Figure 12 (orpart of the A/C module – calledthe “amplifier”). It receives anA/C-on signal from the controlhead (or a pressure switch) andcompares compressor rpm (sensorsignal, Figure 13) with enginerpm. If it detects belt slip, themodule should open the clutchcircuit and trigger a blinking redlight on the HVAC display(Figures 14a and 14b). Refer tothe schematic in Figure 15. If theclutch doesn’t engage but thewarning light also doesn’t flash,the engine idle doesn’t increase,etc., forget the BLC system: Yourproblem is elsewhere. But if thelight flashes and the A/C clutchfails to engage or quickly disen-gages, you do know where to start.

• The belt isn’t slipping? Thenlook for a BLC failure. But if youunderstand the circuit, youwon’t just throw parts at theproblem until that light stopsblinking. Start with a warmed upengine and press the A/C switch.

• But the clutch doesn’t click and engage! Over abrief period, the engine idleincreases, the warning lightflashes, and that’s it. Forgetbelt slippage or the compres-sor rpm sensor, because thatcompressor shaft didn’t turn adegree. If a Toyota electric fanis running at high speed, thatshows the powertrain com-puter believes the engine isoverheating, and in that caseit would not permit engage-ment of the A/C clutch.Denying an A/C requestbecause the engine is runningtoo hot is a standard strategy,so checking the enginecoolant temperature sensorsignal should be part of yourroutine diagnostic procedure.Depending on the computerstrategy, the coolant tempera-ture sensor issue may or maynot trigger the BLC warninglight. However, this is basicallyan electrical/electronic prob-lem, in the circuit before theBLC module comes into play.

The warning light flashes when the belt-lock-controller circuit triggers. Inthis illustration above the light is in thecar outline, and the outside air arrowpoints to it (14a). Warning light on themodel below is a red snowflake (14b). OnMitsubishi Expo LRV, warning light maybe at the underside of the dash, close tothe steering column.

Figure 15: Representative circuit for abelt-lock-controller system. The BLCmodule gets an engine rpm signal fromthe engine control module, a compressorrpm signal from the compressor and twoA/C-on signals, one from the A/C switchand another from the A/C module.

Figure 14a

Figure 14b

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service equipment: theEEAC312B RefrigerantIdentifier, the ACT725Leak Detector, andthe ACTR 5134

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17July 2000

• The clutch clicks or tries toengage, but it doesn’t succeed!Within a brief period the engineidle increase cancels and thenthe warning light flashes. This time, you’ll have to gothrough the circuit, checking allthe inputs, connections andgrounds, and the amplifier(which includes the BLC circuiton many cars). You’ll also haveto test the compressor rpm sen-sor, and although a simple resis-tance check is included in mostshop manuals, the more mean-ingful test is with a scope. Thepatterns are similar from onemake to another (Figure 16). Thesensor is replaced easily oncethe compressor is removed.

Clean Out the Air IntakeIf leaves and other airborne

debris jam the fresh air intake,that’s trouble. If the stuff packs up against a hot blowercontroller or resistor, that can setthe leaves smoldering. Even ifthere’s an intake air filter, thisdebris can prematurely plug the filter and reduce airflow. The manufacturers have tweakedtheir intake grille designs to keep debris out, but nothing is a perfectly satisfactory answer.Nissan has released a number ofreplacement grilles and seals forits vehicles, most recently for the1992-95 pickup, the 1995-97Maxima (cowl cover) and 1995-70(wiper shaft seals) and 1993-97Altima (cowl seals).

Volkswagen has a shield overits intake air filter, but somehowthe filter on an Import Service testcar accumulated a substantial col-lection of leaves and other debrisin just a few thousand miles.

If the motorist complains aboutpoor cooling, maybe the realproblem is poor airflow becauseof accumulated debris. And oncars with no filter, that debriscoats the moist evaporator faceand provides an ideal breedingpen for malodorous fungus. Putyour shop vacuum to work earlyand often (Figures 17 and 18). �

—By Paul Weissler

Figure 17: Plastic shield at the fresh airintake of a VW Passat. With an intake airscreen above it (not shown) and thiscover itself, you’d think the cabin air fil-ter underneath was well isolated fromanything but the finest airborne dust.

Figure 16 (right): Representative wave-forms for the compressor rpm sensor, asmeasured at the rpm sensor terminal ofthe BLC module under the dash, using ascope. The top illustration is from aMitsubishi, the bottom one from aToyota. Simple resistance checks alsocan be made, but are less accurate.

Figure 18: But when the plastic shield isremoved and we pull out the filter, itshows a surprising amount of leaf debrisafter just a few thousand miles.

RPM Sensor Signal

LOCK IN Signal Waveform

Turn Up the Heat