jpitman2

I for one have put a secondary cheap '53' relay out by the AC compressor to unload the small one on the climate board...
jp 83 Euro S AT 55k

dprantl

Not sure exactly how, but I have personally seen it happen more than once in a row with the same compressor but new coil and pulley. It could be that the clutch surface slips and increases the size of the clutch gap, but still not sure how that would draw more current. Could also be a defective new coil...

Dan
'91 928GT S/C 475hp/460lb.ft

dr bob

+++

The clutch coil doesn't know, at least electrically, how well connected the friction faces are, or what torque is applied to the compressor. The clutch coil is mounted to the compressor housing though, where additional load often means additional heat that could migrate to the coil. It's a stretch though, since the clutch also sits in the airflow from the radiator fans.

The original relay contacts are rated for AC operation. Alternating Current, not Air Conditioning... The clutch coil is an inductive DC load, where the collapsing magnetic field on relay contact opening generates a really decent electrical spike. Result is arcing at the relay contacts. This is very similar to the effect on distributor points, in vintage points-and-condenser setups that feed an ignition coil. Porsche added the "suppressor" in the CE panel to help soak up that spike, but it doesn't quench it completely. It really needs that condenser, instead of the diode-in-a-can, but that would add to the inrush load on initial relay close. Lots of things conspire to make relay failure inevitable, at least for those of us who use the AC.

Bilal928S4

I did a rewire at the CE Panel per Alan's instructions for my 91 GT, it works perfectly and takes the stress of off the head unit relay.
If anybody is interested I can post it or send a PM to Alan and he would give you instructions for your model year.

SteveG

Bilal: Pls do. I am currently installing a relay in the engine bay. Since it is nearly done, I will test it when I get back from vaca. On the chance it doesn't work as advertised (b/c of my inexperience at this) I may have to try a second time. I started the CE route but it was just too confusing when I got to re-wiring the plugs; w/o a step-by-step I was lost.

Tony

What amp fuse would be good ?

Randy V

It's all in here, T -

https://rennlist.com/forums/928-foru...re-w-pics.html

Randy V

Help a brother out - no luck on a search.

worf928

FYI: A new out-of-the-box clutch needs 3 amps to engage the compressor.

Tony

I knew i had that part sitting on my bench for a reason...flipp'n 3A fuse was in it as well!

MainePorsche

Hey Ran,
Took me a while but I found Wally's wisdom. He also posted for adding a relay for the fans in case we ever have a problem with powering them. Same principle. I added something I have regarding a standard relay's pin layout.
Craig


https://rennlist.com/forums/6708030-post3.html
https://rennlist.com/forums/8415630-post7.html

Supply - 30 - power in to relay
Trigger - 86 - 'switch' - the on/off of the relay
Load - 87 - power out from the relay

Simple, and I like this approach. Leave out the diode fan stuff until you need it.

Bilal928S4

Here is Alan's procedure for installing a relay in the CE panel and utilizing the non used relay and fuse sockets for a stock look. I have done it and it works perfectly. Thanks Alan.
This is for a 91 GT.
For the 91:

The clutch connection from the HVAC head is on CE pin G21 - the wiring on the CE panel rear connected to this should be moved to connect to your new relay's terminal 87 (output). Terminal 30 on your new relay should connect via a fuse (pick one of the unused ones) to either the battery bus (30), the X bus (X) or the ignition bus (15) doesn't really matter which. Some of the unused fuses may have connection to one of these busses already (depends on car options).

Now add a new wire from CE pin G21 to drive your new relay's coil on relay pin 86 & ground the other coil connection on relay pin 85.

Spare relay socket blocks (unwired) on a '91 should include III (wired but unused - DRL), VI & XX.

Fuse 31 & 32 on a '91 should be unused & available for your use they are totally unconnected inputs (top) and outputs (bottom). Fuse 43 is also wired for an optional telephone (it also supplies the Cat Monitor) but you should be able to use this assuming you don't have a telephone installed.
Its an ignition supplied fuse with its output on CE pin N24. The stock 7.5A fuse should be OK.

Alan
__________________

Randy V

Thanks guys.

Decided to go with the hot point trigger relay approach due to the heavy current leading seen at the control head.

That was followed by a complete AC compressor replacement.

dprantl

So did the clutch get fried after you added the external relay?

Dan
'91 928GT S/C 475hp/460lb.ft