TOM WALKER wrote to ROY WITT:

Mine says the same thing. It even has 4 stages of procedures to check the
AC system. However, it doesn't have a procedure to check out why the
radiator fans don't engage as the engine temps get higher than normal
operating temps when the PCM detects that the system is low on freon.

 TW> From the service manual of a 1998 5.7L F-car (Camaro/Firebird) here
 TW> is the descriptio of the cooling fan controls

 TW> Engine Cooling Fan Description - Electric
 TW> The electric cooling fans are used to cool engine coolant flowing
 TW> through the radiator. The fans are also used to cool the refrigerant
 TW> flowing through the A/C condenser.

 TW> The electric cooling fans are controlled by the PCM. The PCM controls
 TW> the ground path for the three cooling fan relays. The relays are used
 TW> to control the high current flow to power the cooling fan motors.
 TW> Both fans operate together. When minimum cooling is required, the PCM
 TW> energizes cooling fan relay #1 and both fans operate at low speed,
 TW> since the fans are connected in series through cooling fan relay #3.
 TW> Cooling fan relay #2 is open (not energized) and is not used for low
 TW> speed operation of the fans. When maximum cooling is required, the
 TW> PCM energizes all three cooling fan relays. The left fan is still
 TW> powered through cooling fan relay #1, but is now grounded through
 TW> cooling fan relay #3. The right fan is now powered directly through
 TW> cooling fan relay #2 and both fans operated at high speed.

 TW> The PCM will also enable the cooling fans after the ignition is
 TW> turned off. When the engine coolant temperature exceeds 113øC (235øF)
 TW> and the ignition is turned off, the cooling fans will be enabled on
 TW> low speed for 150 seconds.

 TW> Cooling Fans
 TW> The cooling fans are controlled by the PCM based on the
 TW> following inputs:

 TW> The A/C system.
 TW> The Engine Coolant Temperature (ECT) sensor.
 TW> The Vehicle Speed Sensor (VSS).

 TW> Looks like SEPERATE Functions to me controled by a combination of
 TW> Sensors and Relays.
 TW> ---
 TW>  þ SLMR 2.1a þ Typo Tom strikes agaoin
 TW>  * Origin: Fidonet Since 1991 Join Us: www.DocsPlace.org (1:123/140)

         R\%/itt


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