Volkswagen Mark IV Forum banner

1 - 20 of 57 Posts

·
Registered
Joined
·
611 Posts
Discussion Starter · #1 ·
I checked my V5's cooling fans today and they are no longer running on the low speed. I've disconnected them and checked the fans by themselves and the internal resistors are burnt out on both fans.

I have reread the posts by Andymac and others about this problem and I have decided to fit external resistors to repair the low speed function.

From Andymacs previous posts it looks as if the resistor for the bigger of the two fans is approx 0.8ohm.

I have just tried a 1 ohm high power resistor in series with each fan and measured a current of 7.0A (with engine running) for the big fan and 5.5A for the small fan. This means that the big fan will need a minimum of a 50W resistor and the small fan a 30W resistor.

My question is, has anyone actually measured the low speed current drawn by each of the fans when running with the internal (unbroken) resistor? If not does anyone know the internal resistor values for both sizes of fan?

I will publish details of this mod when I have finished it.
 

·
Registered
Joined
·
628 Posts
i'm also intrested in this as my slow speed fans are not working.

it's not causing any bother though as the temp needle never moves over the 90 mark,even if i just let it idle til the high speed fans cut in,is this normal(in a broken sort of sense)i.e what temp is the fast cut in supposed to be?

BigAl- if it's not too much bother could you explain how you tested the low speed supply to the fans so i can check mine.
 

·
Registered
Joined
·
4,528 Posts
HAHAH I was keeping this a secret till id done it, basically my internal repair has worked but it failed after 6000 miles, SO i have been investigating an external repair. What I plan to do is use

2 x 1 ohm 100 watt resistors from CPC and a 4 inch square piece of aluminium as a heatsink.

The other thing I have figured out is it is not essential to push the lower voltage/current down the broken side of the fan, all I will have todo is push the reduced voltage/current down the highs speed line. I figured this out from a wiring diagram on this site http://www.volkswagen.msk.ru/ this means that a plug in resistor heatsink circuit could fix the fans and it will only cost ?20 for all the bits
 

·
Registered
Joined
·
142 Posts
With the high power aluminium clad resistors which I assume you will be using - the power rating quoted is for when it is mounted on a fairly large aluminium heatsink, and 25C ambient temperature.

For a 50W resistor without a heatsink the maximum power is only around 10W and the temperature inside the engine compartment will be higher than 25C, so it could overheat.

If using one of these resistors I would recommend using the next power rating up (ie. 100W) and bolting it to a bracket made from sheet aluminium or copper (which will also help attachment to the car) and placing in the airflow from the fan to aid cooling.

Or a ceramic type could be used without a heatsink, still a good idea to place in the airflow.

Resistor 1ohm 50W aluminium clad from farnell :

http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=3063719&N=401

Datasheet :

http://www.farnell.com/datasheets/6700.pdf

Resistor 1ohm 100W aluminium clad :

http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=652453&N=401

Datasheet:

http://www.farnell.com/datasheets/32367.pdf

Resistor 1ohm 100W ceramic :

http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=3064505&N=401
 

·
Registered
Joined
·
4,528 Posts
Quote: posted by JonJon on 09/04/2005 19:46:12

i'm also intrested in this as my slow speed fans are not working.

it's not causing any bother though as the temp needle never moves over the 90 mark,even if i just let it idle til the high speed fans cut in,is this normal(in a broken sort of sense)i.e what temp is the fast cut in supposed to be?

BigAl- if it's not too much bother could you explain how you tested the low speed supply to the fans so i can check mine.

The temp needle is very inaccurate! believe me the car will be running at higher than 90, the other problem is when you get stuck in traffic on a hot day the high speed will blow a fuse then you will be left with no fans and you WILL overheat. PPS no low speed will also bugger the aircon compressor and lead to a a ?1000 bill, (Ask RFSTEEL)if you dont fix it soon at least take the following precautions carryu a spare fuse with and the tools to change it and run the climatronic only in ECON mode.
 

·
Registered
Joined
·
142 Posts
If anyone wants to post a broken resistor to me I can measure the resistance on a low ohm meter, accurate to 0.01 ohms.

Send me a PM if interested.

Andy
 

·
Registered
Joined
·
628 Posts
thanks for your advice andy

to cut a long story short i could do with a final solution to this from you fine chaps before the weather gets too warm as i have no time at the moment due to working away for the next 2 weeks at least.

your allready so far ahead with the diagnostics it would pointless me starting afresh with my time restrictions.

my only other alternative is new fans,but why if there's no need?

i look forward to reading any advances in this problem in a couple of weeks.catch you guys later.

john
 

·
Registered
Joined
·
611 Posts
Discussion Starter · #10 ·
JonJon: To check fans themselves, disconnect the fan connectors and measure resistance between red/white wire and brown wire to the fans, you will read approx 2 ohms if the fans are OK or it will be open circuit if the internal resistor has failed.

andy not happy: I am not sure yet whether to use the aluminium heatsink resistors and try to mount a heatsink near the fan or whether to use several vitreous enamelled resistors in parallel. For both types, it will be difficult to get sufficient heat dissipation in a sufficiently small size and provide some protection from the elements.

If I cannot come up with a sufficiently compact solution, I will design a simple speed controller based around a MOSFET and a PWM chip. I am fairly fortunate in that I am an electronics engineer designing high power military electronics and have access to all the relevant supplies and equipment.

Andymac: I would like, if possible, an accurate measurement of the resistor value for both the large and the small fans (I assuming the V5 uses the same fans as the V6). Alternatively a measurement of the actual current drawn by each of the fans on the low speed setting with the engine running.
 

·
Registered
Joined
·
611 Posts
Discussion Starter · #12 ·
I have the fans running on low speed again. I used a 1 ohm 100W aluminium heatsink resistor (HSA100) for the large fan and a 1 ohm 50W aluminium heatsink resistor (HSA50) for the smaller fan. Both are mounted on a 6 inch x 6 inch (15cm x 15cm) aluminium plate approx 3mm thick. The plate is fixed in the space under the passenger side headlamp in the space in front of the plastic arch liner.

The resistors are running quite hot,I haven't actually measured their temperatures yet.

One suprise is the current through the smaller resistor is the same as the large one, this is because the two fans are connected together via their red/black wires. This explains why both fans fail together, when one resistor fails in one fan, the other resistor in the second fan tries to run both fans and is overloaded.

For the second phase of this repair I intend to replace the 50W resistor with a second 100W one and increase the heatsink area if possible.

I taken photographs and will post them up when I've finalised the repair and I've worked out how to post them.
 

·
Registered
Joined
·
4,528 Posts
Good stuff, will be doing this next week, I wondered about using a triangular piece of metal cross drilled and placed in the airflow of the fans to reduce the heat. What do you think?
 

·
Registered
Joined
·
4,528 Posts
Good stuff, will be doing this next week, I wondered about using a triangular piece of metal cross drilled and placed in the airflow of the fans to reduce the heat. What do you think?
 

·
Registered
Joined
·
611 Posts
Discussion Starter · #17 ·
Quote: posted by andymac on 17/04/2005 19:25:38

Good stuff, will be doing this next week, I wondered about using a triangular piece of metal cross drilled and placed in the airflow of the fans to reduce the heat. What do you think?

I agree its a good idea to get the heatsink in the airflow from the fans, its just a case of finding a place to put it. I would be very wary about putting it between the radiator and the engine because of the engine movement under acceleration. I have not investigated the other side of the radiator yet.

The place its mounted at present was convenient for a first attempt since there are 3 unused holes in the chassis which made mounting simple without having to drill any holes.
 

·
Registered
Joined
·
611 Posts
Discussion Starter · #18 ·
Quote: posted by ukdub on 17/04/2005 20:00:40

What do vw do with the upgraded fans to stop this problem happening?

I am not aware of any upgraded fans. Weeloon mentioned a modified fan controller, I would be interested to know how it is different if anybody knows.
 

·
Registered
Joined
·
4,528 Posts
Quote: posted by BigAl on 17/04/2005 20:55:50

Quote: posted by ukdub on 17/04/2005 20:00:40

What do vw do with the upgraded fans to stop this problem happening?

I am not aware of any upgraded fans. Weeloon mentioned a modified fan controller, I would to interested to know how it is different if anybody knows.

They dont the fans are considered a consumable by VW expect to replace them every 50000 miles or 3 years
 
1 - 20 of 57 Posts
Top