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Heater fan not working - where to start?


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Hi all! New owner of a 1980 TR7 convertible here, and the heater blower fan isn't working. Where to start looking for the culprit? I've already replaced the fuse in the glovebox fusebox but still no go.

What's the common cause with these refusing to work (on any of the three settings), and what's the sneaky forum fix that everyone knows? :)

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The best way to fix this, or any electrical fault, is to buy a multimeter.

They can be less than £10, and while looking complex, using it just in volt sensing mode (turn the central knob to "20V" DC) will show you where the volts are getting to, and where the aren't.

That will point directly to the fault, or at worst to which length of wiring it is in.

 

A circuit diagram will also be invaluable.

Good luck!

John

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Hello John! Nice to see you outside the TSSC forum!

With what appears to be over 5000000 feet of wiring behind the dash, I was hoping someone would say: "check the red and white wire" or whatever...

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One of the main causes of the electrical problems with the TR7 are the plugs and sockets, There are loads of them, they are un-plated and tend to corrode up. If you need to check around the fan heater controls area you will need to remove the radio console. The bit of plastic where the heater controls come through. Screws on the front and the side. Plus you may need to remove the light section above the radio to get the console out, the screws are on holes facing upwards.

 

Dave

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One of the main causes of the electrical problems with the TR7 are the plugs and sockets, There are loads of them, they are un-plated and tend to corrode up. If you need to check around the fan heater controls area you will need to remove the radio console. The bit of plastic where the heater controls come through. Screws on the front and the side. Plus you may need to remove the light section above the radio to get the console out, the screws are on holes facing upwards.

 

Dave

Done that already Alan - centre radio console is out (so is the dashtop / instrument cluster to replace failed bulbs). I need to know where the three-position switch connections go; my wiring diagram is black and white and yes tells me the wiring connections and colours, but there's no substitute for someone who has done it before telling me to 'look for this or that in this or that position...' At present I'm assuming the heater unit is inside the car and not accessible from the engine bay, not even the wiring?

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Colin, Yes the heater unit and motor is up under the dash. Go to the passenger side foot-well and look up under the dash and you will see the motor on the side of the heater unit and the feed wires.

 

Also there are a couple of plug/sockets up on the passenger side it's worth checking. Water can leak in through the heater water pipe opening in the bulkhead onto them and cause corrosion.

 

Dave

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You may find this helps you. Its my redrawn version of the TR7 wiring diagram for the 81 model and the fan controls are shown on sheet 5:-

 

https://drive.google.com/open?id=166ybTKW659oVdXGNM-Q911n13FZ_LqA9

 

There are two possible issues. The resistor bank has failed or the fan speed control lever contacts are not making contact to earth.

 

I suggest you check that the fan speed control has volts on the live terminals first (obtaining access is a challenge ..). If there are volts the problem is with the switch, otherwise the resistor unit may have failed - loose connection, or burnt out - which can be accessed in the space above the heater fan casing. This does not need the heater to be removed, but Robsport replaced this unit for me. Check this next.

 

Cheers

 

Howard

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That's very helpful, Howard - thanks. I've the dashtop out (the centre panel and instrument cluster) plus the centre console removed, so should have access to most of the bits. I hope!

Is this motor like the early Triumph wiper motors, where they're permanently live, and the switch merely earths the power? I'm debating stringing a power source to the motor to rule out a defective fan motor, but am wary that it may just do more harm than good; however from this it appears if I merely run a fresh earth source to the control contacts I can bypass the earth at the levers and again see how well everything runs?

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Colin, According to the the diagram yes. An ignition switched fused supply is fed directly to one side of the fan motor. The other connection of the motor is fed to the speed control where it switches resistors to control the speed.The other end of the switch is connected to earth.

 

Dave

Edited by DaveR
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May seem a basic answer, but my fan didn't work when I purchased the car. It had been stood for a while and just needed the slider switch connection cleaning.

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Thanks Mike; I'm waiting on a tin of Servisol contact cleaner coming through the post then I'll strip, clean and protect all of the contacts from one end to the other. I'm hoping it's just dirt or rust, so it may be as simple as yours. It's really holding me back as I can't rebuild the dashboard until then, so can't do any other servicing jobs that require the engine running or battery power.

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Latest update is that I've got the engine running, which was a problem in itself, and managed to get the blower working on the 3rd setting on the sliding contact... but only if I bend it about a bit. The other two positions don't work at all, so now I know where the fault lies. Any problems with taking this off the car to clean it properly - there only appear to be two rivets holding it on? Are the sliding switches available new?

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  • 1 month later...

....and another most recent update, for anyone struggling with their heater: I swapped the spade terminals about on the slider control and found that all three worked, but only in one speed. This points to the resistor control on top of the heater being kaput.

I've removed the heater completely, and the resistor unit is now accessible on top with only a spring clip holding it in place. It's very badly corroded so I've ordered a second-hand replacement, which is all that's available; however I've contacted the original manufacturer to enquire if any old stock resistors remain, or what the modern equivalent might be.

DSCF5913.jpg.d10a4ad6e97d938eed6512060cad1b58.jpg

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Brand new thermal sensor obtained today; according to the explanation:

"This is a thermal cutout switch. I'm not familiar with the TR7 but on the Rover SD1 you have two fan speeds, and this switch is designed to cut power to the fan motor if the unit overheats. They tend to fail so that the fan only works on the fast speed, not the slow one. If you want your fan to work as originally intended, you need this switch working."

So I'll solder this one in to the system and see if things work as they should.

Otter.JPG.bdb2649cd7913037abb395b28ad605e5.JPG

 

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