Alfa Romeo Owners Club of Australia Forum

Technical => 160 Series (90, 75, 164 Sedans) => Topic started by: 75Guy on August 18, 2010, 02:35:51 PM

Title: Alfa 75 heater fan problem...
Post by: 75Guy on August 18, 2010, 02:35:51 PM
Hello all, I am at my wits end trying to solve a problem preventing my car from being registered. It's the only thing the mechanic said that needs to be fixed before I can be driving it every day so understandably I'm rather tense right now.

The 75 is a 1985/6 2.5 V6 with air con of the same style used in the same year 90's.

The fan for the heater must be able to blow air onto the windscreen (defog purposes). Turn knob for heater fan and theres nothing.

Heres what I have done:

Checked fuses with test light: aok.
Checked switch with test light: receives power as it should.
Warm car up and hit the fan: nothing.

All other heater related controls work fine. That makes me suspect its the switch but as above, as the switch is changed power is as expected.

Really all I need is it to blow air, thats it even if it is like an asthmatic.

Any help would be great.
Title: Re: Alfa 75 heater fan problem...
Post by: dehne on August 18, 2010, 05:53:11 PM
i have the same prob with my 90, a mate had the same with his 90 and he fixed it it is something to do with the switch behind the unit im pretty sure he swaped the wires around so the fan then was either on or off no adjustment, ill try find out and post it if someone else has not already done
Title: Re: Alfa 75 heater fan problem...
Post by: 75Guy on August 18, 2010, 06:32:57 PM
That would be beautiful. I have had a stress headache all day from this problem...

For a bit I was so mad with it I was going to give up and buy a corolla  ;)
Title: Re: Alfa 75 heater fan problem...
Post by: dehne on August 18, 2010, 06:36:39 PM
thats not mad thats completly INSANE
Title: Re: Alfa 75 heater fan problem...
Post by: 75Guy on August 18, 2010, 06:45:07 PM
I have a absolute love/hate relationship with this car. Today it was all hate. Yesterday (driving to the mechanics from twisty country roads...) it was all love.

I can only assume the balance will shift once I can drive it every day.

P.S Also wouldn't buy a corolla, a twinspark 75 maybe if I went through this again though...





Title: Re: Alfa 75 heater fan problem...
Post by: Typhoon90 on August 18, 2010, 10:06:02 PM
With older cars, every time I have had an issue like this, it has been the resistor pack for the fan motor. In fact, I repaired this exact problem on my 90 on the weekend.
The first thing you need to do is establish that it is the resistor pack. The easiest way to do this is to use  a test lamp and check that the blower control knob has power going in to it and out of it when you turn the knob.
You will need to find the resistor pack if it tests good. On the 90, it is up and behind the bottom of the blower/heater casing. If you are REALLY skinny, you might be able to get to it from the passenger's foot well. At the least you will need to remove the console and find a very bright light. The resistor pack is about the size of  a box of matches and clips into an opening in the side of the blower case. There will be a metal spring clip at the bottom edge holding it in, it is  a circuit board with wire coil resistors that sit into the heater box. The resistor pack will have four wires going to it, one will be  a big red wire, a purple, grey and yellow. I took a photo as luck would have it:
(http://img.photobucket.com/albums/v418/typhoonpud/Alfa/Resistorpack001.jpg)
(http://img.photobucket.com/albums/v418/typhoonpud/Alfa/Resistorpack002.jpg)
I couldn't get a photo of the resistor pack installed, all you could see was the spring clip.
So, you have two options here. One is to join any of the other wires to the red wire to get the blower working, or, spend an extra 10 minutes and fix the resistor pack. The big red wire in my photo is the wire that powers the blower motor, the three other wires feed power from the rotary switch into one of three resistors, which then flows into the red wire, giving you three speeds. See how the red wire has  a piggyback terminal? Pushing any of the other three wires onto this terminal will give you full blower speed in only one switch positon, but fixing it properly is easy if you are this far in.
The resistor pack on most all cars is placed into the heater box, to ensure a cooling air flow over the resistors. With age, they tend to collect leaves etc up against the resistor wires, which overheats them and they either break or burn out. If you look at the resistor pack, you will see a broken wire somewhere, simply replace it, or if it's  a coiled wire, bend it then reattach it to where the old piece has broken off it's terminal. Changing the length of the wire changes the resistance, and hence blower speed on that fan setting, but it's rarely noticeable and you still get three distinct speeds. Once you have it repaired, plug the wires back in and test it with the resistor pack out of the case. You will find a whole heap of leaf litter blows out of your heater box through the resistor pack hole, you can help it out by digging it out with your finger.
Now, bear in mind the description was specific to my 90 with regards location of the heater pack, but I am betting that Alfa Romeo didn't change much between the 90 and 75, they were both 160 series cars and shared a lot of components and auto makers love reusing stuff that already works well.
I hope this helps, it sounds like  a much worse job than it is, but believe me, by far the hardest part is getting to the resistor pack in the first place, and the convenience that a working blower fan brings makes it well worth the effort!

Regards, Andrew.
Title: Re: Alfa 75 heater fan problem...
Post by: 75Guy on August 18, 2010, 10:11:25 PM
Thanks so much for that informative post! Really very helpful.

Tomorrow I'll have a crack at it. If its a case of having the dash out that's no problem - I've had the entire dash out before and once you have done it once it's not all that bad.

I'll let you all know how I go.

Cheers!

Title: Re: Alfa 75 heater fan problem...
Post by: Typhoon90 on August 18, 2010, 10:31:21 PM
You'll just need the console out at worst, you should be able to see what you are doing once it's out. I'd consider pulling the passenger's seat out if you can, it makes access easy, just lay down on the floor with head up under the dash.
The easiest way to find the resistor pack will be to follow the four wires from the back of the rotary blower speed control, or work back from the red wire on the blower motor.

Regards, Andrew.
Title: Re: Alfa 75 heater fan problem...
Post by: Anthony Miller on August 19, 2010, 07:30:43 AM
Well done Andrew, sound advice. Alfa engineers were a lazy bunch in the 70's & 80's (the 75 is just a Joolie on steriods) they used the same switch gear all the way through. Two of my joolies suffered from the same problem and were rectified with replacing or repairing the resistor pack. Good luck 75Guy
Title: Re: Alfa 75 heater fan problem...
Post by: 75Guy on August 19, 2010, 04:05:54 PM
EUREKA!

Everything fixed!

My resistor was a different design to the one you posted but was similar enough to work a solution.

Thank you so much Typhoon and if I ever meet you in person beers will be on me  ;D
Title: Re: Alfa 75 heater fan problem...
Post by: Typhoon90 on August 19, 2010, 05:26:27 PM
Great that it worked out!

Regards, Andrew.
Title: Re: Alfa 75 heater fan problem...
Post by: oz3litre on August 19, 2010, 06:36:51 PM
Quote from: 75Guy on August 19, 2010, 04:05:54 PM
EUREKA!

Everything fixed!

My resistor was a different design to the one you posted but was similar enough to work a solution.

Thank you so much Typhoon and if I ever meet you in person beers will be on me  ;D

Did you have to take the console out or were you able to get at it from underneath? My fan has stopped working too. I have a parts car with a fan that works though.
Title: Re: Alfa 75 heater fan problem...
Post by: 75Guy on August 19, 2010, 10:08:27 PM
Basically what I did was remove the centre console, disconnected the radio and sat it to the side. Then I reclined the passenger seat, laid down and followed the wires until I found the resistors. Hardest part was getting it off theheater itself - stuck on pretty tight.

Apart from that it was easy - as soon as you know what your looking for its very, very easy.

For a quick guide to getting the console out go here:

http://www.users.on.net/~craigf/heaterconsole.htm

cheers!
Title: Re: Alfa 75 heater fan problem...
Post by: dehne on August 19, 2010, 11:10:48 PM
i also have done mine today i left every thing in tacked as i looked at the race car first found where it was then just went straight to the source and bang away it went, shlt i forgot how bloody hot the heater was
Title: Re: Alfa 75 heater fan problem...
Post by: bteoh on August 20, 2010, 01:03:07 PM
Hey Andrew,
I wish I had read your post a few days earlier as that is what happened to mine. Ripped out the whole dash etc on wednesday and found the resistor pack . However, someone had modified it and soldered a 15Amp fuse between the slightly thicker coil. The fuse blew and that's why the fan stopped working?
Any idea why anyone would solder a fuse between the resistor coil? (There's 2 coils on the pack - a slightly thicker coil and a thinner one; the fuse was linked to between the thicker coil) Will tyr to take a pic when I can.
Anyway, will try to blow out any debris in the box - there's a rattle when the fan is on......  :)

Cheers,
Brian
Title: Re: Alfa 75 heater fan problem...
Post by: Typhoon90 on August 20, 2010, 06:26:15 PM
There's a good chance the fan is drawing too much current. If it blew a 15a fuse, something is wrong with the motor I'd say.

Regards, Andrew.
Title: Re: Alfa 75 heater fan problem...
Post by: MD on June 15, 2014, 05:36:49 PM
Radiator fans often draw 18 amps and more on initial start up. Very likely the  heater fan does too. If its appropriate at this location, it is likely to have blown due to too much current going through it for its rating.
Title: Re: Alfa 75 heater fan problem...
Post by: jazig.k on July 06, 2014, 05:52:25 PM
Fixed my twin spark today. Pulling out the resister pack was easy, you can get to it without removing anything (kneel beside the car and twist under the dash, you can see just the metal clip.).

Mine has a single wire, in the centre of the thicker resistor coil, that was melted and blew like a fuse. I soldered a 20a fuse in to replace it. I figure if anything went haywire or whatnot it would be the safe way to repair it.

Initially nothing worked. Tried jumping a wire straight to the red piggyback terminal and the resistor just heated up and got burning hot. Quickly unplugged it and put it back where it belonged.
I knew the motor was getting power now so stuck a finger through a intake vent to spin the fan. It was stiff, It freed up quickly and then started spinning under power because is forgot to turn it off at the knob. Each time it started for a full stop it was a bit slow to start. Stiff I guess. Ran it I. High for a few minutes and watched for smoke...

Now it runs fine.

I have pictures of the resistor and fuse I soldered in, as well as a picture of under the dash pointing to the clip which I'll upload later (pictures posted earlier don't work for me?)
Title: Re: Alfa 75 heater fan problem...
Post by: jazig.k on July 06, 2014, 06:38:49 PM
Here's pointing to the rusty mark where the clip is.
(https://scontent-b-sjc.xx.fbcdn.net/hphotos-xpf1/v/t1.0-9/10388193_10152146886012109_2459943624304313519_n.jpg?oh=65f221b5b1c827426cbf864cc96d749f&oe=54318055)


Wiring configuration.
(https://fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-xpa1/t1.0-9/1545659_10152146886292109_2760005429066301930_n.jpg)


The board with a view of the single wire that burnt out. Also the fuse I soldered in to replace it [I picked 20a because that matched the fusebox fuse]
(https://fbcdn-sphotos-d-a.akamaihd.net/hphotos-ak-xap1/t1.0-9/10520104_10152146885912109_6929559344907676283_n.jpg)

Fuse sits perfectly between the 2 posts.
(https://scontent-a-sjc.xx.fbcdn.net/hphotos-xpf1/t1.0-9/10437759_10152146885807109_7172470224875135151_n.jpg)

Edit: Images dropped out. fixing it.
Title: Re: Alfa 75 heater fan problem...
Post by: shiny_car on July 06, 2014, 09:09:21 PM
Good work. Same resistor board as the V6. I have opened and cleaned the HVAC unit over the past month on my car, which I'll show with my next update.

:)
Title: Re: Alfa 75 heater fan problem...
Post by: MD on July 07, 2014, 08:05:35 AM
No it's not good work at all because its a foul up.
To bridge a fuse over the resistor coil means it is by-passed by no resistance which is part of the fan speed regulation.
That fuse needs to come off to allow the coil resistor to do its job.

Any fuse required needs to be wired well outside of the enclosure so you don't have to pull it all apart to replace it.

Please don't shoot the messenger.
Title: Re: Alfa 75 heater fan problem...
Post by: jazig.k on July 07, 2014, 09:25:09 AM
Quote from: MD on July 07, 2014, 08:05:35 AM
No it's not good work at all because its a foul up.
To bridge a fuse over the resistor coil means it is by-passed by no resistance which is part of the fan speed regulation.
That fuse needs to come off to allow the coil resistor to do its job.

It doesn't bypass the resistor. The only original part about joining those 2 posts is the straight wire that runs in the centre of that resistor coil. The resistor coil doesn't touch those 2 posts, only one of them [this would be the full fan speed, no resistance = full speed].

Slow speed runs power though the small/thin coil then through the thick coil. Highest resistance. Bottom right, through the small coil to middle left then thought the thick coil to the top right.

Medium speed runs power through the thick coil only. Medium resistance. In the middle left, through the thick coil to the top right.

Full speed runs power through the straight wire, which I replaced with a fuse, so it will still pop should anything go wrong, Just like the straight wire did once before. Minimal resistance. In the top right and out the top right.

(https://fbcdn-sphotos-d-a.akamaihd.net/hphotos-ak-xap1/t1.0-9/10520104_10152146885912109_6929559344907676283_n.jpg)

I have full fan control, as original. If I bypassed any resistor the fan would fun full speed at a lower knob level.
Title: Re: Alfa 75 heater fan problem...
Post by: shiny_car on July 07, 2014, 09:41:53 AM
Agreed. The fuse connection correlates with a direct connection, for 'no resistance' and full speed.

Mind you, I haven't measured the resistance across the 'direct connection' terminals, but I expect it to be zero. Makes sense, for full speed (full '12V').

:)
Title: Re: Alfa 75 heater fan problem...
Post by: MD on July 07, 2014, 11:34:45 AM
jazig.k

Only provided feedback from what I could interpret from the photos. Your explanation sorts it out. Good.
Still suggest relocating the fuse to facilitate replacement and fault finding. Up to you.
Title: Re: Alfa 75 heater fan problem...
Post by: jazig.k on July 07, 2014, 11:50:12 AM
Yeah, the picture kinda of shows it but I see it because I did 'read' it while I was holding it. I didn't shoot the messenger.
Yeah I kind of agree with changing it to make it easy to get to, but it really is SO easy to get to without pulling anything out. I expected a pain in the ass job but it's easier than changing then removing a CD player! And I'm not a small guy [6'1" and ~120kg]