Heater Blower and Resistors

[James_EG_940]

Hello all,

Blower fan stopped working the other day on settings 1-4, only blowing on full speed (5). I suspected resistor pack so took it all apart today to check.

The blower has been squealing for a long time and indeed was very rough to turn by hand. Resistor pack I did some digging and it turns out that it was actually just the thermal fuse on the side that has gone. Quite easy to replace and still available: https://cpc.farnell.com/thermodisc/g...84c/dp/FF01030 So if your fan has stopped then check this tiny component before spending £65 on a new resistor pack!

Otherwise though I think it failed in the first place simply due to how difficult it was to move the fan, thus causing it to stall out, pull excessive current and blow the thermal fuse. Does anyone have a known good blower fan (no AC!) they could sell me? There doesn't seem to be much option for anything else now as all the new ones available seem to be for cars with AC. Mine has the wide, flat connector with two locking tabs - one on each short edge.

[Laird Scooby]

Good work on the diagnostics James!

Not sure how viable it would be but you could probably get new bearings for the fan motor, try these people once you've got a bearing number off the old ones :

https://simplybearings.co.uk/shop/

Also if you measure the brushes, you should be able to find some replacement brushes on ebay by typing in the size - don't forget the length will be longer than what you've got in yours as they will have 20+ years of wear on by now!

[James_EG_940]

Thanks, Dave.

I would gladly replace the bearing but I don't think it can be got at non-destructively.

Both the brush assembly and the bearing assembly are peined to the main stator section. This comes apart carefully with judicious use of a hammer and chisel but doesn't offer much use. The nylon fan itself was probably moulded in place on the rotor and the bearing assembly sits between it and the windings. The bearing itself is a fairly standard sealed ball bearing but it's housing is held in place with rivets which would need drilling out. You could carefully cut off the old bearing with a dremel but without being able to take off the actual fan blades you'd never be able to install a new one.

Brushes weren't too bad by the way, still about 2cm left in them, they probably were about 4cm when new going by various other sizings. They are crimped and spot welded in place though, so again not trivial to replace.

A squirt of wd40 loosened the bearing up but it will only be a temporary fix I'm sure.

There are a couple of used fans on eBay right now but I'd rather buy from someone on here who is more likely to be selling a known good one and not just another squealer!

[Laird Scooby]

Can't argue with anything you've said there James, it's more or less what i hinted at when i said i didn't know how viable it would be.

Might be worth checking part numbers for the 740 heater fan as well, most of those were non-A/C so could be an easier find than one for a 940.

[James_EG_940]

Just to update this.

I have reinstalled the original blower fan and resistor pack after repairing both.

Fan doesn't actually have any ball bearings - I was mistaken. It is actually just a oilite bronze bushing at either end of the rotor. I gave a generous slathering of moly grease and worked it all about while cleaning it and the fan is back up and running for now, no longer squealing.

Resistor pack was indeed just the thermal fuse as I mentioned previously. It's not quite straightforward to repair as the original thermal fuse is spot welded and due to being positioned directly in the (damp) air stream for cooling all the exposed metal tends to oxidise. Old fuse was clipped off and the remaining wires thoroughly wire brushed to clean them and bring out the copper. This makes soldering possible and easy. Be careful soldering the thermal fuse as they are single shot devices and obviously can be blown from the heat of the soldering iron - keep dwell time as low as possible.

Hopefully the above will be useful and save people the expense when resistor packs "blow" on their cars in the future. (£60 for some nichrome wire wrapped around a ceramic block by the way!)

[Laird Scooby]

You can make your own thermal fuse if you're stuck James. Take two pieces of single strand copper wire (fairly thick) and solder them in place so one goes to one end of where the thermal fuse would be and the other piece goes to the other point so the two wires are close but not touching.
Tin the area on each strand where the other wire would touch if the wires were squeezed together then hold them together and apply just enough heat from the soldering iron to melt the tining and hold until it cools.
Now if it gets hot again (about 150-160C - melting point of solder) the solder will melt and the two pieces will pop apart again.

Tinned copper wire is better for this really as the uniform tinning along the length enhances its springiness but ordinary copper wire will do.

[quevatre]

Hi James. I have just removed and tested my heater fan - works fine across 12 v . I have also checked the four pins on the connector to the resistor pack while rotating the switch . I get 12v at four different pins depending on the switch position so I'm guessing that's okay too. The thermal fuse on the resistor pack isn't open circuit but when I measure across the resistors instead of seeing a variety of resistances I can only measure a short. I'm guessing that the pack is knackered but my experience is that resistors will go o/c not s/c. Unless you (or anyone) can offer any other advice, I guess my only logical option is to order a new resistor pack . Any other ideas/advice welcomed .

Cheers

André

[Laird Scooby]

Originally Posted by quevatre

Hi James. I have just removed and tested my heater fan - works fine across 12 v . I have also checked the four pins on the connector to the resistor pack while rotating the switch . I get 12v at four different pins depending on the switch position so I'm guessing that's okay too. The thermal fuse on the resistor pack isn't open circuit but when I measure across the resistors instead of seeing a variety of resistances I can only measure a short. I'm guessing that the pack is knackered but my experience is that resistors will go o/c not s/c. Unless you (or anyone) can offer any other advice, I guess my only logical option is to order a new resistor pack . Any other ideas/advice welcomed .

Cheers

André

1. Get a decent multimeter

2. Set it to 0 - 200 Ohms

3. Check each resistance for the blower motor, they will be in the single ohms range, if not less - they are small coils of resistance wire so some will be under 1 Ohm

4. If your meter will not measure under 1 Ohm, measure the voltage on the motor while selecting the different speeds.

You also need to check all your fuses and you still haven't said whether you have air-con in your car or not?

[quevatre]

Hi Dave,

Thanks for your help here. I have the base (Torslanda?) model without aircon. I had looked at the resistor pack and seen 4 x resistances labelled as R36K, R44K, R72K and 1R20K. I took this to mean that the resistors were in the 1000 ohm range but, on reflection a couple of ohms will drop a couple of volts at an amp so I can see that I had made a wrong assumption.

In the attached image B & D would appear to be linked and I guess are ground. A & C seem to disappear off to the same place at one end of the resistor pack where one end of the fuse appears to go to as well. The other four connectors are clearly connected to the four ends of the resistors. Having measured the four way feed on the connector which supplies this, I can see that different pins give 12v depending on the fan switch position so hence my assumption that the switch is fine.

I will go back home (at work at the moment) and re-measure between a/c and the four pins to see what we have. If I find a variety of low resistances as described then I will be scratching my head!

The only other thing is clearly a ‘dry’ joint/connection. I have given all the connectors on the resistor pack a bit of a file. I would have thought that plugging and unplugging them a couple of times would be enough to improve the contacts anyway. Perhaps a bit of WD40 is in order.

PS Liking the thermal fuse idea – simple but ingenious!

Cheers

André

[Laird Scooby]

If you can get a photo of the actual resistor pack Andre that would be helpful. I wanted to check you didn't have A/C as many of them don't have a resistor pack at all.

Looking at those resistances you've listed, 1R20 would be 1.2 Ohms and the R36, R44 and R72 suggest they would be 0.36, 0.44 and 0.72 Ohms respectively. Looking at the diagram on Pg73 of this pdf shows the resistors are connected in series so the theory floated in my previous sentence may not be correct.

http://www.myvolvolibrary.info/Tech_...ction-3-39.pdf

The slowest speed would be on the 1.2 Ohms, next slowest 0.72, then 0.44 and 0.36 Ohms giving the fastest speed before the full battery voltage reached the fan motor. However see my comment above.

Looking at the diagram, if none of the intermediate speeds are working but the fastest is, it points to either the switch or there is a break in the resistor pack somewhere.