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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
    11
    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.

    Cheers.......
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  3. Victor Sullivan

    Apr 19, 2020
    20
    London
    Full Name:
    Victor Sullivan
    Hello Rookie
    I am having the same problem with the heater fan blower speed control on both driver and passenger side. Mine is a 1988 GTB LHD. Had you resolved the issue? If so what was the solution please?
    Thanks
    Vic
     
  4. GTB DownUnder

    GTB DownUnder Rookie

    Nov 12, 2018
    11
    Sydney, Australia
    Full Name:
    Timothy Martin
    Hi Vic

    Not solved yet - it went on the backburner whilst I drove the car instead! Have you replaced the blower motor transistors? I think the issue for me is not at the blower motor (I know the motor works and the transistors are new) but is at the switch/rotary dial end or somewhere inbetween. I suspect the PO had someone fiddling around there trying to fix it and may even have replaced the original switches. My next step is to pull apart the centre console and swap the a/c switch with the fan swtiches (they are the same supposedly) to see if that fixes the issue - if so I know the switches are the problem. There are some articles on repairing the switches but as far as I can see replacements are very hard to come by. Sorry I can't be more helpful but I will post up any insight/answers if I figure it out.
    Tim
     
  5. Victor Sullivan

    Apr 19, 2020
    20
    London
    Full Name:
    Victor Sullivan
    Hi Tim

    Thanks for your answer. No I have not yet attempted to change anything yet but as you suggest its worth a go at swapping the aircon fan speed control for the heater fan speed control to test if its the speed control. Its funny how both driver and passenger sides of my heater fans are faulty rather than just one. The speed control is the same part for aircon and heater according to the parts diagram. I shall let you know the outcome.

    Regards

    Vic
     
  6. Victor Sullivan

    Apr 19, 2020
    20
    London
    Full Name:
    Victor Sullivan
    Hi again. I am sharing this link that shows how to remove the centre console switches in case it's needed. Will attempt the swap this weekend and let you know how it goes. Vic
     
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  8. Victor Sullivan

    Apr 19, 2020
    20
    London
    Full Name:
    Victor Sullivan
    Hi Tim. I have swapped the AC fan speed control with the Heater fan speed control and this solved the problem. This means that both heater fan speed controls are not functioning. Do you know if its possible to repair the controls rather than replace ?
     
  9. Stimorolgum

    Stimorolgum Rookie

    Jan 16, 2021
    8
    Full Name:
    Martin
    Hello !

    Did you manage to repair the heater blower control?

    I’m having the exact same problem, only max blower speed or nothing.


    Cheers/ M

    And one more question, the amber fan light on the dashboard, is it supposed to be on when the fan is on?
     
  10. GTB DownUnder

    GTB DownUnder Rookie

    Nov 12, 2018
    11
    Sydney, Australia
    Full Name:
    Timothy Martin
    Hi there - have to confess to having let the fan controls drift to the 'work in progress list'.....my A/C works well and I tend to use that rather than the fans so still no definitive solution for me. The usual problem for the 'all-off or all-on' scenario is the transistors mounted to the actual blower motors themselves (in the front of the car - quite easy to get to and replace by removing front left wheel, arch liner and an under panel). It could be faulty rotary switches in the centre console (I suspect this is my issue). If your AC works fine fan speed wise then just swap your AC fan control dial with the blower motor dials as this will show whether the dials are faulty or not.

    I believe a specialist could repair the rotary dials (my local Ferrari independent in Sydney can) and some have found a DIY cleaning or just reseating of connectors can do the job too.

    And yes - the amber dash lights should be on when the fan speed controls are in an 'on' position.

    Hope that helps!
     
  11. Victor Sullivan

    Apr 19, 2020
    20
    London
    Full Name:
    Victor Sullivan

    I managed to fix both blower speed control knobs . Once opened up I found loose contacts on the circuit boards. All they need was reheating with a soldering iron and contact made. Blowers now work with speed control.
     
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  13. Stimorolgum

    Stimorolgum Rookie

    Jan 16, 2021
    8
    Full Name:
    Martin
    Thanks for your answers :)

    I swapped left and right heater switches on the center consol and no difference (still only ON or OFF), so must be the transistor on the blower motor in the front.
    Those blowers are exposed to dirt and water so close to the road, can guess they fail.

    Are those Transistors exchangable or rapairable? :rolleyes:

    /M
     
  14. Victor Sullivan

    Apr 19, 2020
    20
    London
    Full Name:
    Victor Sullivan
    Try removing both fan speed controls and open them up. If you see any loose transistors on the circuit board then reheat the solder to make them make contact..this may be the problem
     

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