Trouble Shooter Is it a fault or a feature? When computers are involved, carefully controlled testing may be necessary to de- termine what constitutes ‘normal’ a/c operation.

An Engaging Problem overcharged a/c system? Any help you could pro- Our shop has a problem with a 2002 Chevy vide would be greatly appreciated. TrailBlazer. The hotter the ambient tempera- Jeff Rutledge ture, the more severe the problem becomes. Af- Ardmore, OK Karl Seyfert ter starting the vehicle, the a/c will blow cold air from the vents for a minute or two, then the Thanks for your letter, Jeff. Back when gasoline vent temperature begins to climb. The a/c com- cost about a quarter a gallon, engine cooling fans pressor clutch cycles when our a/c gauges show were bolted solid to the water pump shaft. If the a high-side reading of 375 to 400 psi (the low- engine was running and the was still at- pressure switch stays closed throughout). While tached, the cooling fan was spinning. The higher warm air is coming from the vents, the cooling the engine speed, the faster the cooling fan spun. fan turns at a very slow speed (so slow that you Somewhere along the line, somebody figured can reach down and stop the blades with your out this was unnecessary, and more than a little hand). The problem may continue for up to 10 wasteful. The cooling fan is needed at idle and minutes before the cooling fan fully engages and slower vehicle speeds. But a vehicle that’s tooling begins to pull air through the condenser. The a/c down the road at 60 mph doesn’t need a cooling high-side pressure then returns to normal and fan because plenty of outside air is being forced the a/c works great. The same symptoms will re- through the radiator without the fan’s help. This turn after another cold soak. discovery lead to the development of flex-blade A GM dealership has replaced three low-pres- cooling fans and cooling fan viscous clutches. The sure switches, two electric fan clutches and made latter allowed the fan blades to freewheel when some adjustments to the heater control doors. the extra cooling assist they provided wasn’t They will not attempt any further repairs because needed. This saved some gasoline and cut down GM tech support says the vehicle is operating on unnecessary noise under the hood. within specs. According to them, the fan clutch Fast forward to the beginning of the 21st centu- may take up ry. Today, everything and anything on a vehicle is to eight min- computer-controlled, and the engine cooling fan is utes to fully no exception. Your customer’s TrailBlazer is engage. I equipped with an electroviscous (EV) fan clutch. read the It has the viscous coupling technology you proba- Service bly already understand, combined with electronic Slants tip control. The powertrain control module (PCM) about Trail- monitors sensors for the following parameters to Blazer a/c decide the appropriate fan speed: engine problems in temperature, a/c refrigerant pressure, vehicle the August speed, air temperature, transmission fluid 2003 issue of temperature and ambient air temperature. M OTOR. The PCM regulates a 12-volt pulse width mod- Could the ulated (PWM) signal to the cooling fan relay to cooling fan’s control the EV fan clutch engagement. The relay’s Photo: Karl Seyfert Karl Photo: At first glance this looks like a conventional viscous engagement ON time increases in response to the PCM’s fan fan clutch, but this Chevy TrailBlazer is equipped behavior be clutch ON command. This ON time directly af- with an electroviscous (EV) fan clutch. The EV clutch the cause of fects the amount of time the fan clutch solenoid is is PCM-controlled, so it’s ON only when needed and the problem, energized. When the solenoid is energized, it its speed is infinitely variable. instead of an opens a spring-loaded valve and allows fluid to

4 November 2003 Trouble Shooter STATEMENT OF OWNERSHIP, MANAGEMENT AND CIRCULATION flow from a storage chamber to the fan (Required by 39 U.S.C. 3685) clutch fluid coupling, increasing the fan Editor & Publisher John Lypen speed. When the solenoid is deener- 1. Title of publication: MOTOR MAGAZINE 248-312-2700 gized, the spring-loaded valve closes. 2. Publication No. 00271748 Managing Editor This blocks the fluid path to the fan 3. Date of filing: October 1, 2003 Paul M. Eckstein clutch fluid coupling, reducing fan 4. Frequency of issue: Monthly. Art Director speed. 5. No. of issues published annually: 12 Harold A. Perry The PCM commands the cooling 6. Annual subscription price: $48.00 Detroit Editor 7. Complete mailing address of known office of publi- fan to 100% ON under the following cation: 645 Stewart Ave., Garden City, NY 11530 Tom Nash, AF-SAE, STS conditions: 8. Complete mailing address of the headquarters or 248-312-2708 •When engine coolant temperature general business office of the publisher: Same as above. Technical Editor-at-Large 9. Full names and complete mailing addresses of pub- Karl Seyfert, CMAT, L1 exceeds approximately 264°F (129°C ). lisher, editor, and managing editor: Publisher & Editor Senior Writers •When transmission oil tempera- — John Lypen, 5600 Crooks Rd., Troy, MI 48098; Man- Bob Cerullo, AF-SAE ture exceeds approximately 304°F aging Editor — Paul M. Eckstein, 645 Stewart Ave., Garden City, NY 11530. Mike Dale, SAE (151°C ). 10. Owner: Hearst Holdings, Inc., registered office, Dan Marinucci, AF-SAE, L1 •When a/c refrigerant pressure ex- 1209 Orange St., Wilmington, DE 19801—Stockholder Bob Savasta, AF-SAE, ASE ceeds 240 psi (1655 kPa). owning or holding 1% or more of total amount of stock Mark Warren, AF-SAE, CMAT, L1 of Hearst Holdings, Inc., is: The Hearst Corporation. Contributing Writers •When DTCs P0116, P0117, P0118, 11. Known bondholders, mortgagees, and other secu- Ken Layne P0125, P1481, P1482 or P1484 are set. rity holders owning or holding 1% or more of total Bob O’Connor Even though the cooling fan is under amount of bonds, mortgages or other securities: None. Paul Weissler PCM control, there’s still a viscous cou- 13. Publication name: MOTOR MAGAZINE 14. Issue date for circulation data below: September 2003 Contributing Artist pling involved. So if the PCM com- Russell von Sauers 15. Extent and nature of circulation. mands 100% fan ON, it can take up to No. Production Manager two minutes for the fan to respond at Average No. Copies of Jennifer Herrmann Copies of Each Single Issue 2000 rpm. The lower the engine speed, Issue During Published Production Coordinator Preceding Nearest to Ann Ehlert the longer it takes for the fan to engage. And when the PCM decides to disen- 12 Months Filing Date 248-312-2700 A. Total no. of copies Circulation Manager gage the fan, it can take an additional (net press run) ...... 147,911 147,731 Dale Boehle two minutes at 2000 rpm. The lower B. Paid and/or 516-227-1401 the engine speed, the longer it will take requested circulation 1. Paid/requested outside- Director of Brand Marketing to disengage. In lower ambient air tem- county mail subscriptions Lori Aemisegger peratures, the cooling fan will engage in stated on Form 3541...... 144,372 144,251 248-828-0000 2. Paid in-county Research Director less time; however, it will take longer to subscriptions...... — — Catherine Smith disengage due to the properties of the 3. Sales through dealers and carriers, street vendors, Classified Advertising Manager viscous coupling fluid vs. temperature. counter sales, and other non- Donna Butera You can engage the cooling fan clutch USPS paid distribution ...... — — 800-858-3137 with a scan tool. The ON/OFF command 4. Other classes mailed through the USPS ...... — — National Sales Manager can be found in the engine controls spe- Dave Marlowe C. Total paid and/or requested cial function menu. Try turning the EV circulation (sum of 248-312-2720 clutch ON and OFF, observing how long 15B1-4) ...... 144,372 144,251 PUBLISHED BY it takes for the clutch to respond. Re- D. Free distribution by mail, HEARST BUSINESS PUBLISHING, INC., carrier or other means (samples, complimentary, A UNIT OF THE HEARST CORPORATION member, the slower the engine speed, the longer it will take for the clutch to re- and other free copies): Victor F. Ganzi Outside-county as stated President & Chief Executive Officer spond. Remember, too, the PCM com- on Form 3541/In-county mands the clutch to 100% as soon as the as stated on Form 3541/ George R. Hearst, Jr. Other classes mailed Chairman a/c refrigerant pressure exceeds 240 psi, through the USPS ...... 3,414 3,480 Frank A. Bennack, Jr. and the fan should be up to speed a cou- E. Free distribution outside Vice Chairman ple of minutes after that. If the clutch re- the mail (carriers or other Richard P. Malloch means)...... 125 — President & Group Head, Hearst Business Media sponds faster during the scan tool test F. Total free distribution William M. Wright than it does when the a/c is in use, the sys- (sum of 15D & 15E)...... 3,539 3,480 Executive Vice President & Deputy Group Head, tem may have a legitimate problem. G. Total distribution Hearst Business Media And finally, like many things auto- (sum of 15C & 15F) ...... 147,911 147,731 William K. Baker H. Copies not distributed...... — — Vice President & General Manager, motive, a fix may be available in the I. Total (sum of 15G & 15H) ..... 147,911 147,731 Hearst Business Media form of a software update. Check with Percent paid and/or requested Robert D. Wilbanks the dealer to make sure the HVAC circulation (C/G x 100)...... 97.61% 97.64% Group Controller, Hearst Business Media control module has been updated with 17. I certify that all information furnished on this Kevin F. Carr form is true and complete. President, Motor Information Systems the latest software. A full description Signature and title of editor. of the procedure can be found in John Lypen, Publisher 5600 Crooks Road, Suite 200, Troy, MI 48098 Chevy TSB #02-01-39-005.

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