9two8

Can anyone tell me, should the air-con radiator fan work as soon as air-con is switched on...., or is it temperature controlled...., totally ignorant on this as I thought the air-con would run colder with the help of the fan cooling the rad.
Any advice as always much appreciated .

Ken
80 928 S
5 Speed

UK

WallyP

On the early cars the aux cooling fan is triggered by the temperature of the refrigerant, using the switch on the stem at the receiver/dryer. This isn't very effective.

The change on the A/C activation of the aux cooling fan was made in '87. Prior to '87, the fan is triggered by a refrigerant temp switch, mounted on the stem on the receiver/dryer. This doesn't work too well...

On the '87 and up cars, the fans are triggered by a refrigerant pressure switch, which makes the fans come on as soon as the A/C compressor comes on. This works much better.

For the early cars, one possibility would be to add a relay to the A/C compressor power wire. This would have two benefits:
- Removes the load from the (undersized) relay in the HVAC control head, making it live much longer.
- By adding a diode and another wire, you could power the aux fan from the relay, so that the fan automatically runs anytime that the compressor is on. This will give better A/C performance, and will help engine cooling when the A/C is used.

Here is a thread discussing this...
https://rennlist.com/forums/928-foru...ec-fan-qs.html

9two8

.....,many Thank,s for your excellent advice/ description...., one other thing that confuses me, what is the.., Quote=, (Ring terminal to fit under the sump start terminal ) ie what is the " sump start terminal"

Ken
80 928 S
5 Speed

UK

76FJ55

Believe that should be "Jump start terminal". It is located in the engine bay and is a dirrect connection to the positive terminal of the battery, designed to be used as the connecting point of the positive jumper cable end when jump starting a 928 with a low or dead battery. it is a convinient location to connect electronics that require a non-switch power supply. It is an unprotected circuit so it would be advisable to install an inline fuse in whatever you connect to it.

9two8

Ahh ! that sounds more like it ! thank,s for the input.

Ken
80 928S
5 Speed

UK

Alan

It is a connection to the battery without any switching - in that sense its direct - however it is actually a fairly indirect physical path.

It can be used for starting the vehicle but is not ideally configured for that. The path is Jump post to alternator, alternator to starter, starter to battery. the wiring is sized for its primary job - feeding the CE panel. Ideally I always suggest high power consumption devices be wired to the alternator directly - however this is only a benefit if you can do excellent heavy duty wiring with soldered on ring terminals, good insulation, good cable supports and good routing sized exactly as needed - otherwise just use the jump post.

Alan

9two8

Just posting to say, iv,e carried out the relay mod, as per Wally,s instructions, and fan switches on as soon as Air-con is selected, Thanks, guys.

Ken
80 928S
5 Speed

UK

6mil928

I think my 81 does this too. Must have been changed at some point. It does come on when the engine is very hot too with out A/C running.