328 heater blower diagnosis

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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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

 

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!