E36 blowing fuse 16

[P924]

Hi,

Something keeps blowing Fuse 16 (5amp) on my E36
wiring diagram shows this fuse is for 3 relays for Electric fan (2 relays), and aircon.

I think i've determined the problem is with the fan somehow. With the lowspeed relay and compressor relay removed. I disconnected the temp sensor from the radiator and bridged the connection (to simulate high temp need for fan), and the fuse blew. I replaced the relay with a new one (old one was maybe 3yrs old), and the situation is the same.



I'm not sure where to go from here. Why would the fuse keep blowing when the fan kicks in? its the low current side of the relay, not providing full power to the FAN.

Can anyone help please?

Edited by P924 on Monday 20th August 14:36

[Penelope Stopit]

Good description of the problem
You need to remove all three relays and see if the fuse blows when you bridge the fan switch, if the fuse blows with all relays removed the chances are that there is a short on the wiring from the fan switch to the relay and it could be somewhere along the run close to the fan switch

[P924]

Thanks, Penelope Stopit

with all 3 relays removed, and bridging the temp switch the fuse is ok.

[GreenV8S]

I understand from the drawings that the relay coil receives a fused 12V on pin 85, and pins 86/86b are grounded via the various external sensors/switches. Is that right? Do those drawings come from the OEM? Conventionally pin 85 is coil ground and pin 86 is the coil positive, and if I understand correctly yours are wired backwards.

The coil polarity often doesn't matter. However, it's possible to get relays with an internal flyback diode in parallel with the coil and if you connect these the wrong way round the diode will look like a short circuit and draw too much current. Double check the type of relay you're fitted. Also check the pin arrangement - it looks as if you are using a Type A socket so need to be using a Type A relay, but a Type B relay would look similar at first glance and physically fit without any problem.

Just as a sanity check, I'd remove all relays and confirm the fuse does not blow, then install and trigger the relay you think is causing the problem and confirm that does blow the fuse. You could also check the resistance both ways across the relay coil terminals to rule out an internal fault inside the relay - I'd expect to see well over 50 Ohms measuring in the direction you're powering the relay.

[P924]

Thanks Green. I think you're onto something with the relay types. They are very similar, but slightly different.

[P924]

ok, so old relay that came out is Type - B, hence the problem with that one.

New relay which replaced it, is Type-B too but with a diode.

will try and get the right part. Thanks everyone,

[GreenV8S]

It seems odd that the wrong relay is fitted and it's apparently wired contrary to the standard. If that was me I'd want to double check the actual wiring connections to those terminals and not take the drawings at face value, just in case the drawing was wrong.

[P924]

About 3yrs ago I had the car machine polished, and when it came back the fan was permanently running. I assumed the relay was caked in dust and being held open.

Went to a local motor factor, offered the old relay, and asked for a replacement, cursory check myself it looked correct. (I didn't know about the two types)

Roll forward to now, and I realise A the Aircon doesn't work, and B nor does the fan. Replace wrong type relay with new wrong type, and this time actually check if it works. And of course it didn't. What I didn't realise was neither had worked since the first replacement relay.

[Penelope Stopit]

P924 said:

Thanks, Penelope Stopit

with all 3 relays removed, and bridging the temp switch the fuse is ok.

Ok, there is definitely something wrong with a relay or relays

[3795mpower]

Reading your description you’ve not mentioned if the fan itself runs ok ?

My only similar experience was years ago with an E34.

The electric fan was partially seized drawing too much current and blowing
The fuse. It only happened when the AC was in use as the cooling system
Never gets itself into a situation where the aux fan is needed.

So after 6 months lay up, a warm day using AC the fan blew.

For info the fan should spin freely with a tap of the finger (power off of course)
If the fan has friction and doesn’t spin / stops instantly after you flick it then it
Is siezed. This will instantly blow the fuse.

[P924]

Thanks 3795mpower,

The fues blowing, is the one that powers the low current side of the relay, it's only 5amp. Fan turns freely, and appears ok, though I havent tested it. Guess it hasn't been used for the last 3 years

[P924]

just fitted the correct relay, and working perfectly now.

Thanks guys.