HEATER BLOWER RESISTOR

[neilmoxon]

I return to a subject associated with many threads throughout the years but strangely, not recently. So here goes; my MY82 924L heater blower fan stopped working completely last summer whilst the lower speeds hadn't worked for several years prior.

Anyway, late in 2022 the car went for a service at Northway Reading (recommended by the way) with the throwaway comment "any chance you can have a look at the heater whilst you have the car". They got back to me within a day apologising that neither blower fan or fan resistor spares were available from Porsche or their other parts suppliers. Anyway, cutting a long story short, I collected the car running like a dream but still with no heater blower; however, I departed Northway with a brain full of useful advice and contact numbers along with a new task for my retirement!

After some further research I have discovered that the system is the same heater blower fan set-up as the 924S and early 944 with common failures! Unfortunately 2 months later, I am still struggling to fix my problem. Whilst I think that I have successfully sourced a replacement fan using the VW part number for a Mk2 Scirocco, sourcing a resistor and possibly the harness remains stubbornly out of reach. I have considered adapting resistors from other models and even researched DC motor pulse-width modulation to overcome the overheating issues but I lack the expertise so can anybody on the Forum help?
Fingers crossed, Neil.

 

[neilmoxon]

My thanks to the member who has replied to the post with a suggestion and link; unfortunately, the resistor which is giving me the problem is the heater blower version pictured and the item which you discovered for sale is apparently the cooling fan resistor, incorrectly named by the vendor. But may I say that your input has been much appreciated. Neil

 

[russmw]

Hi,

Replacing the fan resistor was one of the first jobs it did on mine after buying it as I only had the top speed working. The first 2 speeds go through the resistor (actually a small voltage should go to the motor with the ignition on but the speed set to zero) to limit the power supplied to the motor but speed 3 goes straight to it which makes your issue interesting if it’s not working flat out.

Do you know of any voltage is reaching the speed switch or resistor at all??

just found this which I think is the same part - just need to get handy with a soldering iron

https://www.heritagepartscentre.com/uk/171971281ef-heater-blower-resistor-including-wiring-harness.html

thanks

 

[neilmoxon]

Hi 'russmw'

Apologies, I didn't go into the full detail on my first post but the failure on my car turned out to be a double whammy: The fan motor was seized and that had blown the 25A fuse. In addition, a resitance tester told me the central coil (2.3 ohm) of the large resisitor pictured was blown so fan position '1' was open circuit, and as you are obviously aware, with the way the system is designed this also breaks the circuit for fan position '0'. Subsequently, with a replacement fan and new fuse fitted, I proved position '3' and '2' worked; then with a jumper lead short-circuiting '1' confirmed that '0' had proper continuity.

My problem is therfore (as a minimum) to fix the 2.3 ohm coil for position '1' but I think that would be short-sighted. I believe my car's resistor isn't the original so these things don't appear to have much longevity and i'm not that surprised considering the heat generated! You have kindly confirmed the Heritage Centre resistor/harness to be a possible, if not the best, solution but they are currently out of stock with a re-stocking date estimated as the end of March. Another uncertainty I have is the resistance values for each coil of their item and whilst the image shows it having 4 terminals only 3 are harness wired - mmmm!

Hence to one of my original questions as to alternate methods for a fix. I can source 1, 2.2 & 3 ohm resistors of 100W rating which I think is sufficient and believe that I can fashion a bridge to match the OEM values. Also then fabricate a heat-sink mounting to better the 40-year old design which still fits within the plastic cowl and avoids the melting problems which I have read about. However, that will take some time and effort; an enjoyable retirement task but hence my introduction of the modern PWM solution and asking if any member has gone down that route.

Out of interest, is your replacement an OEM item? If so are there printed ohm values or do you have measured resistances of the 3 coils to confirm my values? NB: My 0.9 ohm coil measures a slightly odd 1.6 ohm, obviously I cannot measure the 2.3 ohm coil and the 2.6 ohm coil is about spot-on!

Thanks again. Neil