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Question
On my 2002 Trailblazer, I don't think my PCM is "telling" my cooling fan clutch to "come on". I have replaced the fan clutch and it's doing the same thing as the old one. I can see the fan turning but I can never HEAR the fan turning, (like I used to), even when the temperature gauge moves up to 230 degrees in traffic, and returns to normal when I start moving again. How can I test to see if the clutch is "getting the message" or not?
Certainly you would expect to hear the fan work when it IS moving air, and not merely freewheeling loosely on the fanclutch bearing, so I certainly accept your observation as good evidence that something might be amiss. In fact, it would surprise many people if you were to tell them that fans - and propellers and pumps, for that matter - have a power requirement that is related to the speed of operation by a CUBE power law. Fans take little energy to start, so many feel they take little power to run as well - the truth is that, until cavitation relieves the load, the required torque and power increases dramatically.
You have replaced the fan clutch itself, and the situation is unchanged. This suggests that the clutch activation signal is not reaching the clutch. You can verify that as a start, and then proceed to work back to find along the circuit to find the problem, apparently an open circuit.
I have no data on your 2002 Trailblazer, so I can only suggest that - with the engine OFF - you find the point of connection nearest the electric fan clutch, and connect a digital multimeter to it, set up to detect the 12-14V signal when it is applied. Then, start up and let the vehicle warm to the point where the fan should activate. (You may have to arrange your setup to include an extension wire so that you can monitor that clutch activation signal from the cab as you drive around.)
Should a 12-14V signal become present, you can then pull over and stop and then, with the engine running, take a good look at and listen to the fan, and also place your hand in front of the radiator grill (NOT repeat NOT behind the moving fan!) to note if air flow can be felt. Wetting your hand will make it more sensitive as moving air will quickly evapourate the water and cool your hand.
If the fan IS working, end of problem.
If the fan is not working but voltage is present, there is an open in the sliding contact assembly that brings power to the clutch.
If the fan is not working and voltage is not present, shut things down and then do a continuity check back through the circuit using an ohmmeter or continuity tester.
Any continuity problem most likely is a bad, possibly corroded, connector. I have written a number of things about dealing with those over the past three months I have been doing this. Check out some of those answers if you wish, or query me again.
Good luck and cheers ... EGK
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Answers by Expert:
Ernest (Ernie) Kenward
Expertise
The challenges I most enjoy are thoughtful technical questions of a trouble-shooting nature in both electrical, power electronic and mechanical systems, mainly automotive but also machine control and small-machine PLC applications. Please note, however, that I am NOT a walking shop manual! I DO, however, make it a point to have those manuals and other service literature for those vehicles I DO own, and highly recommend that anyone serious about maintenance or modification of their vehicles do the same; MOST of your answers WILL be found there. For that matter, I do NOT go out of my way to acquire shop manuals for any vehicle I do NOT own! That being the case, any general query to me along the lines of "What is the meaning of this code read from the ECU of my 2015 XYZ?" or "Where is the fuse for the windshield washer pump found?" (try your car's electrical distribution panel for a start!) will not go far. What I do offer is a pretty good collection of literature, insights and hands-on experience with 1950s to 1980's Ford products (plus a developing database of information and practice with the Mercedes diesel cars), along with an engineering perspective and the ability to design and implement custom control, electrical and mechanical subsystems for vehicles. For that reason, I am happy to make my thoughts and efforts available to those who are of like mind and/or are seriously making a point of learning about their vehicles. Use the Opportunity to Learn!
Experience
A key skill in my work and hobby pursuits both is STRATEGIC TROUBLESHOOTING. I am a senior instructor in Electrical Engineering Technology at a leading Canadian polytechnic, my areas being Electrical Power and Industrial Control, electrical and electronics design and manufacturing, and AutoCAD and related CAD/CAE software - plus equipment problem-solving and new equipment design and prototyping.
Hobby-wise, I have 30-plus years of experience in auto restoration, mostly in electrical and mechanical systems. Ongoing projects include a 1959 Edsel Corsair, my 1978 Ford E250 class-B motorhome conversion, and the care and upkeep of my Mercedes 300CD.
My vehicles become engineering test beds for electrical and mechanical upgrades as ideas present themselves. This includes the design and production of circuit boards to restore or enhance features for which no OEM replacement parts are obtainable, or where better specifications or reliability can be had via newer concepts. Regarding the E250 RV conversion, I designed and continue to revise a custom power distribution system, managed by a Programmable Controller (PLC); this has made most revisions as easy as uploading new firmware as I develop it.
The "mini" PLC is a powerful device for custom automotive control systems. One good example (there are many) would be the Moeller "Easy Relay"; these offer a wealth of control, monitoring and variable-and-status display options for such projects. A good example project which has worked well is that one for my RV noted above, which has been on the job - revised in firmware only - for a decade now. It is a load management and charging control system to avoid the sulfation-induced early failure that often befalls deep-cycle batteries used in RV power applications. The battery installed in 2003 lasted long enough to more tnan pay for the PLC that contributed to its longer life ... and the PLC will be there for the next battery as well!
Organizations
IEEE - senior member ... past WCC Student Activities;
SME - senior member ... past chair, greater Vancouver chapter chair 318;
Edsel Owners' Club - have served in various capacities on chapter executive during seventies;
have been Power and Driveline resource on the Edsel Owners' Club "E-team" for more than a decade.
Education/Credentials
Graduate of UBC
Awards and Honors
Certificates of appreciation from IEEE and SME for work in student and chapter activities
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