some more 172 loom questions (rad fan)

[Matteh]

I'm just trying to tidy up the 172 loom to fit my mk1 and want to sort out the fan...

as far as I can work out, i've not removed anything from the loom that should effect the running of the fan - unless its controlled by something in the dash?

there are 2 connectors that come off the same branch of the loom that you could plug the fan into, which one should connect to the rad fan?

It seems that the fan just constantly runs at max when you plug it in - what could be causing this?

is it related in any way to the vehicle speed sensor that plugs into the gearbox, as i've removed it from my loom

 

[bmh.01]

In the 172 the fan is controlled by the ECU and has two relays which can power it, one is for the high speed the other for slow speed for the a/c. There should be two relays in the engine relay/fusebox one of which will put 12v directly onto the fan for full speed and the other will pass 12v through a resistor to give the slow speed.

Not that any of that directly helps you but assuming you haven't altered the wiring thats how it'll be setup.

 

[mini-valver]

Just wire it permanent live with a switch in the dash somewhere dude. Simplicity is where it's at

 

[Matteh]

yup, i've got the 2 relays connected up, haven't touched them, its just that the 12v one seems to be always on?

where do the 2 plugs connect? both to the fan?

 

[Matteh]

Just wire it permanent live with a switch in the dash somewhere dude. Simplicity is where it's at

pah, can't be dealing with having to control it myself

worst case scenario i'll connect it up to a fan switch like the mk1 and wire that to the relays instead... although I would like the 172 system working for the variable speed!

just can't see why it shouldnt work as i've not touched anything to do with the fan

on a slightly related note, the F4R seems to get up to temperature fairly quickly!

 

[mini-valver]

The slower speed is for the AC though, which you havent got, lol....

Switch in the dash

 

[Matteh]

how does it know i've not got the AC? what do people do when they remove it?

 

[mini-valver]

I thought the slower speed only came on when your aircon is turned on..... I'm probably wrong, lol!

 

[ditz]

nope my aircon is in the skip. slow speed comes on first and normally cuts in and out very rarely does high speed come on,
on sunday it was going slow/fast/off though as it was so hot

 

[ditz]

oh, i got sidetracked there..

if its running permanantly its seeing the wrong resistance value from the coolant temp sensor.
get it plugged it at a garage (dont need to be clip just a scanner that can show live data) and see what temp it reads.

dont you have a 1.6 cts? probably down to that

 

[Matteh]

I do - fantastic memory!

I thought they were the same , but I'll get an F4R one (assume they're common on 1*2s?)

iirc, wayne had the same problems with his - fan running constantly - don't recall him using the 'wrong' CTS

 

[ditz]

well ideally you want so see what resistance is giving.
im looking through the data i have access to now i cant see a resistance curve for a f4r temp sensor,,
you'll want to compare it to that.
it will also be making it overfuel so worth checking

could be something as simple as a sticking relay, swap the two over see if it stops.

how much of the 172 loom is it running? and is it fast or slow speed on constant.

ideally you want some live data out of it as you could see if the ecu is getting an AC request on that also as that would make the slow speed run, but again may be irelevant depending how much of the 172 loom is there

 

[Matteh]

I've stripped all the wires that run from the ecu to the loom plug as I've got nowhere to plug them in

I've also removed little things like the wire that connects the alternator to the plug (for the dash light) as i've replaced them with mk1 items (same for oil gauges) - but those things are ECU independant

I get a constant 12v on the first plug when you run then engine and it continues when the engine is switched off (though I've not checked for how long, i got bored after a few minutes! )

Some resistance values would be great, I could get the multimeter on it (got a temp probe too)

 

[bmh.01]

Temp sensor resistances:

-10c = 8.5kohm
25c = 2kohm
50c = 810ohm
80c = 309ohm
100c = 114ohm
120c = 87ohm

 

[bmh.01]

Also to add you should have a pin on both relays that'll be 12v all the time anyway but that shouldn't be put onto the fan until the either relay closes so either the ECU is closing the relay(s) (going along the CTS route) or the relay is fudged and it stuck closed hence try swapping them over like ditz says.

Does it run rich from a cold start like it should? One way of seeing if the ECU is getting the coolant temp right, but still check it with a meter.

 

[Matteh]

those values, are those between the 2 wires that go to the ecu? the white and the black?

 

[ben_p]

the ecu also has a speed signal imput. maybe thats why the fan is f**king up?

 

[bmh.01]

those values, are those between the 2 wires that go to the ecu? the white and the black?

Yes, the temp sender is just a thermister.