A Volkswagen Up had an interior blower fan that was not operational. On the initial scan, no AC or blower system faults were present.

A diagram was sourced for the climate system to investigate the blower circuit. Using the wiring diagram, it was found the fuse supplying the blower circuit was without power. Backtracking the circuit to the Auxiliary Power Relay, the power supply to terminal 86 was also missing, with the ignition in the run position. Terminal 85 is a permanent earth at this relay. The power supply to this relay terminal 86 comes directly from the ignition switch.

The ignition switch was the issue, so a replacement switch was fitted. With the new switch installed, the interior blower worked correctly. As a bonus, the customer had not mentioned that the rear wiper had not worked since the fan had stopped. The power supply for the rear wiper also come from the Auxiliary Power Relay.

So, if both the heater blower and rear wiper on the VW Up fail, it is common for the ignition switch supply to the Auxiliary Power Relay to be the issue.

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