Heater blowers on full speed

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mat_fenwick
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Re: Heater blowers on full speed

Post by mat_fenwick »

Thread Bear wrote:That is what I do not understand. The blower, having been changed for a working one in and out of the car, it should work, to my head layout.
Only if the fault is with the motor.
If I cross the PCB directly it works at the differing speeds.
What do you mean by cross the PCB, and which one? I'm assuming you mean the one behind the heater dials rather than the one in the blower housing, but we need to be sure.
That leaves the relay on the blower.
There is no relay on the blower housing - that's the transistor. I don't mean to sound pedantic but if you are trying to test it as a relay this may just confuse the issue.
if the motor runs jumped to the PCB it must be working. Indeed I drove last night with a jump cable onto the PCB contact.

Can you explain this a little more - it may be a big clue as to what is wrong? The motor is fed with an ignition switched +ve supply so am assuming you've run an earth wire from the motor to somewhere, but which contact on which PCB?
I have my spare blower relay/resister here. There is a soldered in strap on this that seems to not be soldered to the back of the resister but just pressed against it. It has a loose end. What is this, a crude over-heat off.
This thread may help. The transistor earths through this strap so if there is poor or non existent contact, it won't work.
The problem here is that without a wiring diagram it is not possible to check each wire
There is one in the Haynes manual if you have one - I have posted the one for the AC equipped cars below. There are some extra components, and there are two blower motors but the principle is the same.

Image

658 is the transistor in the blower housing. Ignore 270 and 288 - they won't be fitted to yours.
Image

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Re: Heater blowers on full speed

Post by Thread Bear »

Thanks for input. I missed it before I had to go over to the house to receive goods in, while I attempted to resolve the blower. The good news is I have achieved a result. The bad news is I am not totally certain how!

Yes I was effectively jumping bits on the heater knob PCB board but I was reluctant to put full current through, in case there was something I could upset the other end of the circuit. I have a wire with a fuse holder on it, so if I short something, it takes out a bit a loose fuse wire. Great when you do not know what your doing!

Indeed I was kind of treating the resister like a relay. I worked out roughly what was going on today from your, someone's, earlier comments.

I was driving around with a power cable clipped to the faster blower take off from the lighting terminal on the dash PCB board. What with that and the innards of the column hanging out it was a dangley day.

All my manuals are packed somewhere in a shed full of moving stuff. However I found a Petrol Manual in the 1.4 so used that to try and understand the wiring, much as you can with the diagnostic diagram you just included, thank you. Not studied it yet, as only just got in and off to Evesham later

Anyway I think I was fundamentally misunderstanding the principle to which the system works.

Being as the blower resister PCB was the part I had not really fiddled with I took the old one off the failed blower assembly. It looked as if you could unscrew the plastic cover on removal from the blower assembly. This via a small star drive self tapper. However either this one was corroded, or you cannot, as the PCB broke under the tug to free the four spade connectors. Having broken it, I decided it might not have died in vane, so pulled it apart. Cannot say I fully understood what I was looking at, but seeing how it went together, I carefully cleaned the other one up. Bit of a sod, as a need to be gentle, and not easy to get in the corners. Put this back on, and hey presto. The system worked!
At least this is consistent with the electrics on this car. So many corroded joints and it was this I think that was hanging things up. But quite what was not contacting I could not tell you. I have to say I got crud out of the pressure contacting bar, so it might have been there. It remains to be seen if I have really got to it. Proof will be some long period of functioning heater. Otherwise something else is loose or not correct.

So what is learned. It is worth cleaning the Blower PCB insert carefully if it might be the culprit in a none functioning heater system? I can quite see the scraper on the knob inside being the weak point, but the Blower is near enough outside, so can corrode more than the rest of the system. I will hang onto the bust PCB as the resistor could be re used.

Thanks for taking the trouble to provide an answer. I will study the wiring to see if I can really Identify what might have been the problem better.
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