Maintenance Object Repair Procedures
555-233-123
10-328 Issue 4 May 2002
Fan Replacement Procedure
NOTE:
The procedures in this section pertain to both non-variable speed (standard)
fans and variable speed fans.
First, determine which fans are defective:
NOTE:
The following instructions are for servicing a Medium Cabinet. For a Small
Cabinet (only two fans in the rear), follow Step 2A below, but start from the
rear of the cabinet.
1. If any fan is not rotating, a more detailed inspection is required to
determine why the fan has stopped operating. The fact that a fan is not
spinning is not always proof that it is damaged. Since each front fan is
electrically in parallel with a rear fan, an internal short circuit in a front fan
prevents power from reaching the rear fan (and vice versa).
Remove the fan assembly cover by pulling the cover outward. Remove the
power connector from each inoperative front fan.
2. The following must be done to determine if the front fan or the rear fan has
failed:
a. Test the front fan:
Measure the input impedance between the (+) and (-) input
terminals of the front fan with an ohmmeter. IMPORTANT: Attach
the “common” lead of the ohmmeter to the fan’s (-) input
terminal and the “ohms” or (+) lead of the ohmmeter to the
fan’s (+) input terminal.
Follow the guidelines in the table below:
b. Test the “paired” rear fan:
From the front of the cabinet, use a voltmeter to measure the DC
voltage across the two female contact pins in the connector housing
of the fan wire harness removed from the inoperative front fan in
Step 1. (This voltage is the same voltage seen across the input
terminals of the paired fan in the rear of the assembly.)
Input Impedance Fan Analysis Action Next Step
2.0M < ohms < 20M Good None Go to Step 2B
ohms < 2.0M Short Circuit Replace Go to Step 3
ohms > 20M Open Circuit Replace Go to Step 3
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