IBM 343 manual Cooling Subsystem, Ambient Temperature Control

Cooling Subsystem

The cooling subsystem contains a fan array (as shown in Figure 9) consisting of two 80 x 38 mm fans and two 40 x 28 mm fans to cool the server board and other components. A fan failure is indicated by one of the fault LEDs located on the front panel.

OM12820

Figure 9. Fan Array with Four System Fans Installed

Air flows through the bezel, over the peripheral bay and the hard drive tray, passes through the fans, over the server board, and exhausts through the rear of the chassis.

Each fan provides a tachometer signal output to the server board to indicate a fan failure.

Ambient Temperature Control

The server board contains a pulse-width-modulation (PWM) circuit, that cycles the 12 VDC fan voltage to provide quiet operation when system baseboard temperature is low, and there are no fan failures. Under normal baseboard temperature conditions (less than 45 ° C), the fan power circuit supplies an effective fan voltage of 7.0 VDC. When the baseboard temperature exceeds 45 ° C, the fan control circuit ceases cycling and delivers 12 VDC. Following a baseboard temperature excursion above 45 ° C the fan voltage does not reenter PWM mode until the baseboard temperature drops below 45 ° C and all fans are operational.

The cooling subsystem’ design meets acoustic and thermal requirements at the lower fan speed settings. At the higher fan speed settings, thermal requirements are met for the maximum ambient temperatures but acoustic requirements are not met.

26 xSeries 343 Hardware Maintenance Manual