EV fans for the 5.3L engine in 2003

[TxDoc]

Thanks to Cop Dodger:

 

Cooling Fan clutches have been used on GM vehiceles for many years, because they improve fuel economy and emissions, and contribute to lower engine noise levels. Historically, most rear-drive vehicles have been equipped with a thermostatic fan clutch, or in some cases, an electronic fan.

 

The 4.2L engine in the 2002 Chevy TrailBlazer, GMC Envoy, and Oldsmobile Bravada uses an all-new PCM-controlled Electro-Wiscous (EV) cooling fan. In 2003, this same device will appear on the 5.3L midsize truck engine.

 

When compared with the conventional fan clutch, the EV fan offers several benefits:

- Improved A/C idle and ciry traffic performance

- Reduced noise

- Reduced A/C compressor warranty, because the A/C system operates at a lower head pressure

- Reduced parasitic losses, for improved fuel economy

- Reduced false engagements at stop light idles

 

The conventional thermostatic clutch is a fluid coupling, belt-driven by the engine. The amount of fluid in the coupling is controlled by a bimetallic coil spring attached to a valve. More fluid is admitted into the coupling at higher temperatures, causing the fan rotation to increase. At lower temperatures, the spring closes the valve, decreasign fluid in the coupling, and the an rotation decreases.

 

Fluid is pumped from the reservoir in the fan clutch in to the coupling by the ation of the fan shaft.

 

The EV fan clutch also operates by controlling the amound of fluid admitted into the couplinjg. But insted of bimetallic spring, the valve is operated by an electrical solenoid.

 

The solenoid is controlled by a solidstate device, operated by a pulse-with-modulated (PWM) signal from the PCM. As the commanded state of the fan clutch increases, so does the ON time of the relay. And the relay ON time directly affects the amount of time the solenoid in the fan clutch is energized.