heliflyer

Hi Alan,
I intend adding an additional relay on the CE panel to power the AC clutch and would be grateful for your comments on my proposal.

I intend using the output from the AC controller that normally goes to terminal K21 to power the new relay coil (terminal 86), - the other side of the coil to earth(terminal 85).

I will then provide a 12v feed from an ignition on source (VS VIII if I can find it) to terminal 30, and then run the output from terminal 87 to Terminal K21 on the CE Panel. This will then control a 12v feed to terminal M12 on the CE panel as the per the original layout.

I have attached a diagram of my intended mod.
Thanks

Alan

Yes rather like this - make sure the supressor is on the clutch side of the relay (as with yours). Some years have a feed to the ECU to bump idle with AC on - I recommend keeping this before the relay - this will need a swap of this wire. There are ample Ignition (15) feeds on the later CE panel. Look at the input side (top) of all the ignition supplied fuses.

Alan

WallyP

While this is a neat approach to extending the life of the small relay in the control head, I would like to suggest a slightly different approach.

Leave the system as-is all the way to the wire at the compressor clutch. Disconnect this wire.

Procure a good 12 vdc relay with heavy duty contacts that is rated for continuous duty.
Install the relay on the fender panel near the jump start terminal.

Wire the relay:
Supply - Install a Black 12 gage wire from the jump start terminal to a 30 amp in-line fuse then to the supply terminal of the relay.
Trigger - Hook the black wire that fed the compressor clutch to the trigger/control terminal of the relay.
Load - Attach two black 12 gage wires here. One goes to the compressor clutch. The other goes to a diode, then to the aux cooling fan. Leave the existing wires on the aux cooling fan.

With this set-up, the small A/C head relay sees only the operating coil of the added relay. The compressor clutch load is taken by the added heavy-duty relay.

Any time that the A/C compressor is operating, so is the aux cooling fan, improving A/C performance. The refrigerant temp switch triggering of the aux fan is not too effective. The diode prevents the normal coolant temp triggering of the aux fan from back-feeding the compressor clutch.

Done properly, this system is safe, effective, and fully reversible.

dr bob

I would look for X-bus instead of bus 15 for the clutch feeder so the compressor is dropped out when the starter motor in engaged. That also gets the EMF fom the coil off the ignition switch contacts and other loads.

Wally's suggestion is very good also, keeping the cooling fan running whenever the clutch is engaged.

For those with '87+ cars, the second control-head relay contact is dedicated to telling the LH and the fan/flap controllers that the AC is engaged. If you decide to add a SPST relay in the CE panel and eliminate the tiny relay in the control head, you'll want to add a diode in place of that second contact.

Alan

Wally - this is the default functionaity on late model cars (S4+) - fans always run with AC on - agree earlier years (incl. the new CE panel '85/'86 models) don't work this way and what you propose may be a good idea in all those cases.

It is neater for the later cars to do everything on the CE panel - there is always at least one spare relay socket suitable for this and once the panel is out and you have sourced the connectors - all the large connectors are easy - readily available Ford tabbed types work (though the original Porsche versions are much better quality).

Both are available but the Porsche versions are much harder to find and are approx 10X cost (but the quality difference really does justify the price).

Alan

heliflyer

Thanks guys for all the suggestions.
My car is a late model 86 Euro Auto (16v) - early car layout but factory S4 brakes, so I think I'll go with Wally's suggestion and have the aux fan running whenever the ac clutch is engaged.

Cheers

Alan

Dr Bob -

The suggestion here is primarily a preventative measure as I understand it - protect the small dual contact AC head relay while it still works - as such the second contact set is still operative.

As a replacement after mini relay failure its more complicated...

As I understand it - the second contact set of this relay is quite independant (in & out) and links the main temp mixing unit to the recirc flap control (and in some years the water valve also) - the functionality here was modified a little over time as the HVAC evolved. Seems primarily designed so the main HVAC temp control unit can detect when you are in AC recirc mode. On later models this may be a little redundant since you are always in AC mode when in Recirculate (so couls use the direct switch feed instead). The functionality here seems a bit bizarre but I think is just a legacy artifact.

I believe the LH connection is always made on the CE panel from the primary clutch contact set.

Alan

SharkSkin

An extra relay can be incorporated into the CE panel in a 100% reversible way. I have written up the steps that I took to do so here(details will be different on an 86).

Here's a pic showing how I marked and insulated unused wires from the seat belt relay: