328 heater blower diagnosis

Discussion in 'Technical Q&A' started by GTB DownUnder, Oct 4, 2019.

  1. GTB DownUnder

    GTB DownUnder Rookie

    Nov 12, 2018
    Sydney, Australia
    Full Name:
    Timothy Martin
    Hi All

    Thanks in advance for any help - this is one of the many 'heater blower only works on full speed' issues. I've read other posts I could find and tried solutions but I think I now need help from those more accomplished than me. Car is a RHD Australian delivered 1988 328 GTS (pre ABS). It is relatively new to me and this issue was present when I got it.

    I've managed to restore the AC variable fan speed by replacing the transistor in the ac ducting as per other posts - all good and pretty straight forward. I assumed that he left/right heater blowers needed the same solution as they also only worked on full speed.

    So I replaced the transistors in the blower motor ducts but when I reconnect still no variable speed control - still only operate with speed switch on full

    I'm an electronics/car electrical newbie but have done the following (see attached sketches for the connections I describe):
    - verified that 12V is supplied with ignition to acc via the blue/red wire in the car harness connector leading to right side blower (red wire on the blower motor side of the connector)
    - checked for voltage change in the other three connections whilst the right side fan speed control switch is operated ....... multimeter shows no voltage changes at all across these connections

    I'm unsure of next steps. Assuming the new transistors are not faulty (as suggested in other posts I used motorola 2N5886 as replacements - same as I used for the AC fix that was successful) - does the fault lie somewhere else? Everything I've read suggested the transistors would be the issue. Given there is no voltage change (at the fan motor harness) as the heater fan control switches are operated from off to full could the problem be in the switches themselves? I believe the AC switch is interchangeable with the others so I think I will try swapping that in but beyond that I'm at a loss.

    I appreciate any help/guidance - and pls make any instructions idiot proof.

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