Cooling fans on full question

CatsEyes · 09-12-2011, 06:42 PM

Hi folks,

I'm currently troubleshooting several electrical issues bequeathed me by POs. Home-wired immobiliser installed ham-fistedly; other odd bits of home-wiring. These have caused no end of troubles (some documented here previously). And fixing them is fussy and time-consuming. Sigh.

First on the current to-do list, though, is a cooling-fan issue.

On my 1986 NA (RHD) both cooling-fans come on full when I turn on the ignition, and stay on all the time. They turn off again when I turn the ignition off. But all that work is presumably going to kill the fans eventually.

I followed the trouble-shooting procedure at Calrks Garage:

Cooling Fan Operation and Troubleshooting

The results are these: they confuse me a bit.

When I jumper the fan switch connector terminals 2 and 3 one fan (only) comes on full-bore (the left or passenger side RHD). When I jumper terminals 1 and 3 nothing happens.

With the connector unplugged and ignition turned on both fans come on full-bore as usual.

With the air-con relay removed both fans come on as usual.

It's not clear to me from this if the problem is the fan relay in the fuse-box or the thermo-fan switch. It also strikes me from the above that there could be another possible issue: the wiring to the thermo-fan connector. But I'm not expert enough to be sure, and the fan relay is too expensive an item to purchase in error.

Any advice appreciated.

One other thing. I have a spare fan switch, and was going to swap it and see, as a further trouble-shooting step. But for the life of me I can't get the old switch out of the radiator with the coolant drained and space created above. It seems firmly stuck (over-torqued?). But the radiator thread's plastic, I think, so brute force doesn't seem an option. Any suggestions?

Thanks in advance.

CatsEyes · 09-13-2011, 03:39 PM

Well, no suggestions so far...

However, going back through the archives at the Rennlist forums, I did happen upon a thread there titled "bad cooling Fan Switch, a short circuit, or what????" from 2003, which does suggest other options for these same symptoms than the switch or $200 relay. Specifically the A/C system and switch, which can cause the fans to run all the time.

Unfortunately I can't seem to find a way to link that thread here, but a forum search will find it easy enough.

In case this helps others...

Rasta Monsta · Rasta Monsta's Garage

Wow, the late relay is that much? My S was doing this, and it was in fact the "AC relay" but I don't recall it being very expensive.

CatsEyes · 09-13-2011, 03:58 PM

Hi Rasta,

The cooling fan relay is over $200 here at Pelican. I see no cheap options, at least visible from here (Australia). The AC relay's much, much less.

Here's the link to the thread at Rennlist:

bad cooling Fan Switch, a short circuit, or what???? - Rennlist Discussion Forums

That person in 2003 had the same issue as me: it didn't seem obviously to be either the switch or the relay. In the end he paid hundreds at $80 an hour for a shop to tell him it was 'the A/C receiver dryer switch' (his words).

I'll read up on that switch from the factory manual (Clarks Garage has nothing), and check it.

If it does indeed prove to be the problem I'll post here for any other poor schmucks like me who go around in circles on this one. I've now drained the cooling system, jumpered the connector, checked the wiring, struggled with the switch, opened up the relay (pristine), only to be confounded at all turns!

John_AZ · 09-13-2011, 04:19 PM

The previous relay interchange I once mentioned has gone up in price as well:

'88 951 A/C Blower Fan Speed

The ballast resistor can be soaked in vinegar to clean:

Ballast resistor-blower fan

Removing the radiator fan relay/switch. Yes it is plastic and maybe the PO has used JB Weld to fill in the threads that were stripped.

Use gentle force and remove the fan relay and if you do find the threads are messed up---again, JB Weld thinly applied is your friend.

GL
John

CatsEyes · 09-13-2011, 06:19 PM

Thanks, John.

Hadn't heard of the ballast resistor before: will look it up here and locate.

All the symptoms seem to point away from the thermo-switch, but it would be good to change it anyway, to remove it as a possibility. I think I may need a better socket, too.

I should add (since you're a great reminder on this) that I've thoroughly cleaned all the grounds recently. Time-consuming, but with excellent results.

Ah, if I'd had any idea what I was getting myself into when I purchased my car a year ago! But I'm on the great 944 journey of discovery now...