Guys,
I am going to apply a secondary relay into the HVAC circuitry per Wally's write up.

https://rennlist.com/forums/6708030-post3.html

Wally states to have a diode placed in one of the load lines from this relay that powers the cooling fans. He doesn't however state what the specs of the diode should be so as to effectively block back current when fans are powered up for engine cooling.
Would any one know what kind of amperage I am looking to block ?

Thanks in Advance,
Craig

 

Wally is talking about the aux electric fan fitted to the pre S4 cars. SO this mod doesn't apply to your S4.

 

Thank you John.

 

Sorry, I should have been clearer - the basic mod of adding the relay is applicable to all MY and is good insurance for that under-rated relay in the HVAC head.

It's just the diode for the aux fan that is not needed for your S4.

 

I read you correctly.
Thanks for the thought to clarify.

 

John,
I had posted to 'dacfan's' thread below regarding the secondary relay. This prompted me to generate this thread. dacfan has an MY 84 with aux cooling fans, and he needs to know the correct specs for such a diode. Could you advise ?

 

It should be at least a 35 or 40 amp diode as per Wally's post about using a 30 amp fuse
(derating the diode)

 

Yes, thank you. That would make sense.

 

On an S4+ the cooling fans are always on when the AC is on so you already have this.

Personally I would not add a relay in the engine compartment - there is always at least one spare relay spot on the CE panel - I'd add it there - thats where Porsche should have placed a propper replaceable clutch relay in the first place...

The AC clutch line alweays runs through the CE panel for every year - you can intercept it there quite neatly. For the larger relay terminals (the only ones you need) you can use inexpensive Ford terminals as subsitutes (less good than stock types - but adequate for this - or get the real thing from eagle day).

Alan

 

Alan,
I have already developed my plan. It will be under the hood. The relay will be in a waterproof electronic component box that will be smartly placed. The wires exiting this box will be through nicely fitted rubber grommets. The box will be placed where exposure to water will be practically non-existent. I just received the new hvac controller, so I'll start later. I will post some pics.
Thanks again for all your help and advisement.
Craig

 

Craig,
Thanks for helping me out! I'm getting together everything I need from my engineering office (read junk room) at the radio station I manage and starting on the project in the morning. My head unit relay is damaged already as I'm only getting 8 volts but that's enough to latch the relay so I'm hoping for the best.