Heater Blower HELP!

andycadabra · Post by **andycadabra** » Fri Apr 09, 2010 3:54 pm

I have a similar problem to the Ian, the OP. Fan speed wavering, sometimes working on full, sometimes not at all, or just blowing weakly.
I'd be interested to know if replacing the motor solved the problem,or whether it was the PCB/resistor. I have an old '87 16 TRS for spares, so hopefully that motor would be the same as the one in my '92 17TZD?.

Post by **Defender110** » Sat Apr 10, 2010 3:23 pm

andycadabra wrote:I have an old '87 16 TRS for spares, so hopefully that motor would be the same as the one in my '92 17TZD?.

What your hoping that one's buggered aswell?

andycadabra · Post by **andycadabra** » Sat Apr 10, 2010 6:36 pm

It did work years ago and the car had only done 70k. My TZD, 125K

andycadabra · Post by **andycadabra** » Wed Jun 02, 2010 9:03 pm

I had assumed it was the fan at fault but a direct feed from the battery to the fan connecting lead, made it spring to action like it hasnt for ages, so it may be the transistor/resistor/pcb at fault?.
Yet I cant figure out where it is since the fan's connecting lead (yellow wires) disappears into the bulkhead. if its in the fan housing it would have hindered the fan working when connected to the battery direct?

Post by **Defender110** » Thu Jun 03, 2010 12:24 am

Have you had a look at the fan speed controler board behind the switch? it is a very common BX problem?

andycadabra · Post by **andycadabra** » Thu Jun 03, 2010 1:32 pm

Thanks Defender, you think it might need replacing? I've tried to remove the facia panel (containing controls and 2 vents) to see, but removed knobs and obvious screws behind them, but while I can pull out the bottom its fixed somewhere at the top, and cant figure out where and how.
Maybe i can bypass the system and install a dimmer switch?!

Post by **mat_fenwick** » Thu Jun 03, 2010 2:00 pm

So you've removed the Torx screws behind the knobs? The top of the panel is held in by a couple of spring clips into the air vent trunking - you have to remove the two centre vents (which it sounds like you've done).
I too have the same problem, despite 3 different (used) boards, so I replaced the fan transistor with a new part - the problem remains so I think I have just been unlucky with second hand parts. The transistor is in the fan trunking (on the rear) between the motor and the entrance to the cabin. You can get it out without removing the fan assembly, but you have to remove the plastic scuttle panel (base of windscreen) first.

andycadabra · Post by **andycadabra** » Thu Jun 03, 2010 5:27 pm

Hi Mat - You too eh? I heven't removed the vents - can't figure out how to - once they are removed the spring clips become visible?
As far as the transistor is concerned I can feel a connector going into rear of fan motor in scuttle is that where the transistor is?. I have a BX for spares with same system - should I try replacing pcb first?

DFF53 · Post by **DFF53** » Thu Jun 03, 2010 8:45 pm

I got so sick of trying to fix mine that i just unplugged motor and connected to a 12v power supply to test if it was ok , and it was. Next what i did was made up a new loom connected to variable resistor and cigarette lighter plug So now when i have to use the blower i just do the normal, opening the vent control which also controls the fan speed, set the temp control and level control as usual but then plug the cigarette lighter plug and adjust the variable resistor to my required fan speed. The hardest bit was running the cable neatly through the bulkhead into the channel where the fan sits. I kept all the bits and didnt butcher anything so i can reinstate the factory system when i want to. To be safe the cigarette lighter plug is fused.

Post by **mat_fenwick** » Thu Jun 03, 2010 11:21 pm

To remove vents lever them out with a slim screwdriver from the side. Then pick up small springy bit of metal that drops out in the least accessible place. (It sits around the pivot stub and provides a bit of friction so the vent stays in the desired position).
It will be obvious once the vents are removed!

Yes, that is the transistor assembly, I wouldn't worry about that if you can swap with a known good PCB.

andycadabra · Post by **andycadabra** » Fri Jun 04, 2010 12:31 am

DFF53 - good to hear there's a workaround! A variable resistor is the same as a potentiometer I believe, as used in electric guitar volume controls I believe. Yes have some of those - do you route the live through it or the neutral? Would a dimmer switch work the same?

Thanks Mat, I figured out how to extract it, and managed not to lose the friction springs. Cleaned up the PCB a bit, but it seems like such a simple thing not much could go wrong. Anyway I substituted the one on my old spares car which had much the same effect. Weak and wavering fan..

I suspect it's the transistor - there is a small random popping noise coming from the fan motor area when it's running which might be it. Will swap it for one from spares car and see. That'll have to be next week though. Away for the weekend and hoping for no traffic jams in hot weather, or we'll cook!

andycadabra · Post by **andycadabra** » Mon Jun 14, 2010 11:57 am

since returning from my weekend away, the fan has been working perfectly, so either
1. a delayed reaction after applying WD-40 to PCB and all connections or
2. the therapeutic effect of driving at more than 50 miles an hour, or
3. my car's miraculous powers of self correction, which also appear to have stopped the water pump leaking in recent months.
And with the car running better than ever, it seems like the Phoenix has finally risen from the ashes of scrappage temptation of 6 months ago..

andycadabra · Post by **andycadabra** » Tue Jun 22, 2010 5:59 pm

I forgot to mention the odd fan speed behaviour seemed to be exacerbated by turning the fan to full, or the last centimetre before full.
So having had it work perfectly for a week, couldn't resist the temptation of seeing if it'd really fixed itself by turning it up to full, and guess what? Back to square one - weak and wavering. Might have to look at the transistor after all...

andycadabra · Post by **andycadabra** » Fri Jul 02, 2010 2:15 pm

Well, I removed the heater fan and housing in order to get at the transistor, to find something that looks like a circuit board from the 1940s set on a corroded aluminium heat dispersing plate. After cleaning all contacts with WD-40 and reassembling everything seems to be fine.

The thing that puzzles me is that having taken the heater fan, and housing out of my old spares car, an '87 16TRS, I've found that in the position where the transistor is positioned on my '92 17TZD, there was nothing but a removable plate. This would suggest that the transistor was perhaps originally located inside the car, yet if it needed cooling so badly that it needed to be fitted on a cooling plate directly in the path of the airflow from the fan, wouldn't it have overheated anywhere else?. And if they had created a provision for it in the housing by 1987, why didn't they originally fit it there?.

Another puzzling thing is that the 1987 housing sat quite happily fixed by 3 nuts, yet the similar 92 one has an additional bracket above it - none of the screws to remove it are accessible, and without it being removed, or bent, the housing can't be removed. Without it the housing did rock back and forth a bit (unlike the 87 one), but managed to make it firm by tying some chicken-wire around it and pulling it towards and fixing it to the bulkhead.

Anyway, glad to have that in-car hurricane restored in time for this weather!

Vanny · Post by **Vanny** » Fri Jul 02, 2010 5:04 pm

That sharp horrible pointy bracket is easily removable with the right tools, namely a stubby ratchet screw driver.

The aluminium plate isn't for keeping the PMOS cool, but is the whole reason the PMOS is there. The device adjusts the blower level based on the temperature of the air coming into the car. Might sound pointless, but at 70MPH both the amount and temperature of the air entering the blower compared to idle speed are very different. Also the current draw (and thus speed of the motor) will change according to atmospheric temperature. When the aluminium plate gets cooled, the PMOS adjusts its power output.

It's kind of temperature controlled relay really.

(PS i hope i've explained that correctly)