Fan Clutch 4.2 Question

[markhart1]

Hello all,
New to this forum and really appreciate all the good information. I have a 2005 LS and I'm really pleased. I've only had one issue, a whining serpentine belt pulley that was replaced. I'm very impressed with the 4.2, smoothest engine I've ever had. I like looking under the hood and seeing what's-what and I would like to know how the fan clutch on these work? I notice it's belt driven, yet has wires connected to it! Mine is working fine, I'm just curious and like to know how things like this operate.
Thanks, Mark

[ScarabEpic22]

Hello all,
New to this forum and really appreciate all the good information. I have a 2005 LS and I'm really pleased. I've only had one issue, a whining serpentine belt pulley that was replaced. I'm very impressed with the 4.2, smoothest engine I've ever had. I like looking under the hood and seeing what's-what and I would like to know how the fan clutch on these work? I notice it's belt driven, yet has wires connected to it! Mine is working fine, I'm just curious and like to know how things like this operate.
Thanks, Mark
Welcome to another Pacific NW member!
I think that makes about 5 of us to about 500 MI guys!:laugh:

The fan clutch is computer controlled, it spins until the engine warms up and then disengages and only comes on when the engine is overheating. I know how it works, but my explanation isnt that good, sorry about that.

BTW, where are you actually located? It just Pacific NW in your info. Thanks, and welcome!

[markhart1]

Interesting. I wonder why they wouldn't just use a electric fan instead?
I'm based out of Gig Harbor and travel WA-ID-MT

[EnvoyON22s]

here's an pretty damn good explanation that should help clear things up a lil: FOUND THIS INFO ON: http://www.findarticles.com/p/articles/mi_qa3828/is_200311/ai_n9306187


Thanks for your letter, Jeff. Back when gasoline cost about a quarter a gallon, engine cooling fans were bolted solid to the water pump shaft. If the engine was running and the fan belt was still attached, the cooling fan was spinning. The higher the engine speed, the faster the cooling fan spun.

Somewhere along the line, somebody figured out this was unnecessary, and more than a little wasteful. The cooling fan is needed at idle and slower vehicle speeds. But a vehicle that's tooling down the road at 60 mph doesn't need a cooling fan because plenty of outside air is being forced through the radiator without the fans help. This discovery lead to the development of flex-blade cooling fans and cooling fan viscous clutches. The latter allowed the fan blades to freewheel when the extra cooling assist they provided wasn't needed. This saved some gasoline and cut down on unnecessary noise under the hood.

Fast forward to the beginning of the 21st century. Today, everything and anything on a vehicle is computer-controlled, and the engine cooling fan is no exception. Your customer's TrailBlazer is equipped with an electroviscous (EV) fan clutch. It has the viscous coupling technology you probably already understand, combined with electronic control. The powertrain control module (PCM) monitors sensors for the following parameters to decide the appropriate fan speed: engine coolant temperature, a/c refrigerant pressure, vehicle speed, intake air temperature, transmission fluid temperature and ambient air temperature.

The PCM regulates a 12-volt pulse width modulated (PWM) signal to the cooling fan relay to control the EV fan clutch engagement. The relay's ON time increases in response to the PCMs fan clutch ON command. This ON time directly affects the amount of time the fan clutch solenoid is energized. When the solenoid is energized, it opens a spring-loaded valve and allows fluid to flow from a storage chamber to the fan clutch fluid coupling, increasing the fan speed. When the solenoid is deenergized, the spring-loaded valve closes. This blocks the fluid path to the fan clutch fluid coupling, reducing fan speed.

The PCM commands the cooling fan to 100% ON under the following conditions:

*When engine coolant temperature exceeds approximately 264°F (129°C).

*When transmission oil temperature exceeds approximately 304°F (151°C).

*When a/c refrigerant pressure exceeds 240 psi (1655 kPa).

*When DTCs P0116, P0117, P0118, P0125, P1481, P1482 or P1484 are set.

Even though the cooling fan is under PCM control, there's still a viscous coupling involved. So if the PCM commands 100% fan ON, it can take up to two minutes for the fan to respond at 2000 rpm. The lower the engine speed, the longer it takes for the fan to engage. And when the PCM decides to disengage the fan, it can take an additional two minutes at 2000 rpm. The lower the engine speed, the longer it will take to disengage. In lower ambient air temperatures, the cooling fan will engage in less time; however, it will take longer to disengage due to the properties of the viscous coupling fluid vs. temperature.

You can engage the cooling fan clutch with a scan tool. The ON/OFF command can be found in the engine controls special function menu. Try turning the EV clutch ON and OFF, observing how long it takes for the clutch to respond. Remember, the slower the engine speed, the longer it will take for the clutch to respond. Remember, too, the PCM commands the clutch to 100% as soon as the a/c refrigerant pressure exceeds 240 psi, and the fan should be up to speed a couple of minutes after that. If the clutch responds faster during the scan tool test than it does when the a/c is in use, the system may have a legitimate problem.

And finally, like many things automotive, a fix may be available in the form of a software update. Check with the dealer to make sure the HVAC control module has been updated with the latest software. A full description of the procedure can be found in Chevy TSB #02-01-39-005.

Copyright Hearst Business Publishing Nov 2003
Provided by ProQuest Information and Learning Company. All rights Reserved

[EnvoyON22s]

hope that gives u a better idea on how it works...

[tblazed]

If you hurry you can read the GMTechlink article about it here

http://www.gmtechlink.com/images/issues/arcv_pdf/7_02_e.pdf

Unfortunately GM is shutting down public access to Techlink after the first of the year (really p'sses me off GM!) so you might go to the Techlink archives, download and save any old Techlinks that are of interest. Yet another attempt to dumb-down the customer IMO, and I told GM about it. Reading Techlink helps keep old techies like me interested in buying GM products. I like to know how things work too!

[markhart1]

Hey guys,
thanks so much for the info. I do find this kind of stuff interesting and understanding it might help me (allo f us) out down the road when trying to diagnose or describe an issue to a tech. I never even knew about the tech newsletters and found it very informative. Thanks again

[willnavarro]

Welcome to another Pacific NW member!
I think that makes about 5 of us to about 500 MI guys!:laugh:

The fan clutch is computer controlled, it spins until the engine warms up and then disengages and only comes on when the engine is overheating. I know how it works, but my explanation isnt that good, sorry about that.

BTW, where are you actually located? It just Pacific NW in your info. Thanks, and welcome!

Hello, I have an 02 trailblazer and presents this problem: when I start the engine the fan clutch engages and it blows 100% (a little noisy), then when temperature rise up until 75°C, it desengages until the engine comes overheated (about 120°C) and engages again, but its too late to cool the engine. why is this happening? it´s the thermostat wrong?

[markhart1]

Howdy,
I would suggest you use the "search" feature for this forum and type in "fan Clutch". You'll find their have been quite a few posts describing it's function and diagnoses. Fortunately, I haven't had any issues with mine, it's the factory original. Best Wishes, Mark

[markarock]

Search feature is highly recommended.

Until then, here is one of the best threads on this topic.

http://forums.trailvoy.com/showthread.php?t=19604