RW>TOM WALKER wrote to ROY WITT:

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

Since the Engine temperature function has priority so the fans should
have run in high speed. Since it did not it indicatas either a bad
engine block sensor, a problem with one of the Relays, or an unusual
problem with the vehicle speed input to the PCM.

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

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

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

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

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

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

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

RW>         R\%/itt


RW>--- GoldED+/W32 1.1.5-31012
RW> * Origin: Texas Lone-Star - Texan, American, USAian  (1:387/22)
---
 þ SLMR 2.1a þ Typo Tom Strkes Again
 * Origin: Fidonet Since 1991 Join Us: www.DocsPlace.org (1:123/140)