New to this - C3 THE PLOT THICKENS

[Alex Gray]

Hi all, first post from me as a new member. My late dad had a beautifully restored 1979 C3 that he rebuilt from the ground up. Following his passing I have inherited Jess (his name for her). I have vowed to take care of her and continue to enjoy her as he did.

Electrically trained on houses, cars I’m a complete amateur and seem to have an issue with the radiator fans not coming on at the trigger temperature. Quick Look and tracing of cables has led me to find a mysterious black box screwed down to the inside of the engine bay. The thicker power cables come in and out of this device so I’m assuming this is a relay of sorts. Some smaller gauge cables also come in and I’m assuming they contain some ignition and stat signals??

I’m not entirely sure on rules of engagement in these forums so apologies if this is cheeky but can anyone point me towards a wiring diagram so I can continue fault finding please?

If anyone has experienced this problem and has any tips that would also be amazing

Thanks
Alex

 

[johng]

Electric fans will be an after market fitment. It might help if you can see who they are made by, I know several members have also fitted electric fans so they should be able to help with a circuit diagram. How do you know the fans aren't coming in at the trigger temperature, what temperature are you expecting?

 

[Forrest Gump]

Hi Alex, welcome to the Club and nice that you’re taking on your Dads pride and joy.

As John said, the electric fan set up would not have been original fitment on your car, so you won’t find a factory wiring diagram as such. As you’ve already determined, the relay is just switching the fans when the temperature sensor switch tells it to. The fans draw high amps hence the relay.
Are the fans coming on at all or just not at the expected temperature? You can use a jump wire across fan supply side of the relay to check the fan. The temp switch will ground to switch.
I would expect the fan to switch on at around 190 / 195 then off at 10 or so degrees lower.

 

[Alex Gray]

Thanks Forrest and John, appreciate you both reaching out.

Some extra detail I missed. The fans would always come on at around the 200 mark, as per the dash gauge. Then when I was taking her for a spin she started to overheat, I got her back to garage and realised then that they had stopped coming on at the 200 mark and actually are not operating at all any more.

Interesting about the after market addition, my simple brain is wondering how the engine would be cooled without them?? Question for another day perhaps.

Ok, I’ll try and jumper across to see if it’s the fans power circuit, assuming they run that’ll rule that out and mean I need to look at the sensors??

Thanks

 

[Alex Gray]

Not the best photo, but from what I see online with the SPAL dual fans, they seem to have two individual relays where I have this unit

 

[Chuffer]

Hi Alex , welcome to CCCUK and hope you have lots of fun keeping your dad`s pride and joy on the road . The other guys have given you good `pointers` to look into and can`t add more as my 1980 C3 runs a standard viscous couple fan with electric add on`s . Where are you based ?

 

[Alex Gray]

Thanks Chuffer, I live in Fleet in Hampshire

 

[Forrest Gump]

Not the best photo, but from what I see online with the SPAL dual fans, they seem to have two individual relays where I have this unit

Ah, okay you have a nice control module box. I reckon you do still have two relays inside that - one for each fan. Check them, but I bet the fans are okay. More likely a fault on the switching side - check you have 12v at the ignition feed and then try grounding the temp sensor wire.
The original cooling fan would have been a big metal fan mounted on the end of the water pump which normally work well, no electrics to go wrong, but we try and “modify“ things!

 

[Roscobbc]

A fair number of C3 owners have removed the single viscous coupled fan assembly and shroud in fayour of Spall twin electric fans. And one can see the logic of doing that for many users as they are sold as a kit and easily sourced. As yes the relays can potentially be a 'weak spot'.
Whilst the twin fans are generally adequate for stock and power performance small blocks they are potentially questionable in terms of cooling power on larger capacity and modified/higher output engines. The reason why is simple. The large stock fan is surpringly efficient IF the OEM shroud is in place and undamaged.- IF the viscous coupling (and therefore fan) is functioning properly (they can fail) - and IF the radiator is in good order, and the engine waterways not obstructed by crud from lack of using a 50/50 anti-freeze mix (and water pump impeller in good order).
From a technical point of view twin fans mounted to the rear of the radiator will only pull cooling air through an area the diameter of the fans - unlike the stock fan and shroud assembly (when/if) in good order will pull cooling air across the whole radiator surface if all OEM seals are in place.

 

[Forrest Gump]

A fair number of C3 owners have removed the single viscous coupled fan assembly and shroud in fayour of Spall twin electric fans. And one can see the logic of doing that for many users as they are sold as a kit and easily sourced. As yes the relays can potentially be a 'weak spot'.
Whilst the twin fans are generally adequate for stock and power performance small blocks they are potentially questionable in terms of cooling power on larger capacity and modified/higher output engines. The reason why is simple. The large stock fan is surpringly efficient IF the OEM shroud is in place and undamaged.- IF the viscous coupling (and therefore fan) is functioning properly (they can fail) - and IF the radiator is in good order, and the engine waterways not obstructed by crud from lack of using a 50/50 anti-freeze mix (and water pump impeller in good order).
From a technical point of view twin fans mounted to the rear of the radiator will only pull cooling air through an area the diameter of the fans - unlike the stock fan and shroud assembly (when/if) in good order will pull cooling air across the whole radiator surface if all OEM seals are in place.

Agree, GM had done their homework with the stock set-up for sure, and that’s how engines were cooled in those days before electric “everything”. All cars for decades now (including very high powered) use electric fan radiator cooling of course. Electrics fans usually use shrouds so can still pull air through the whole rad surface.
I was following a C8 when we were out the other week. It was a cool morning but the amount of heat coming out of the rear deck vents was surprising, distorting the view of the back of the car.

 

[Chuffer]

Thanks Chuffer, I live in Fleet in Hampshire

Down in the Sunny South Region then which always seems an active region of the club so can get to meet other members . I am up in the East Midlands .

 

[Roscobbc]

Agree, GM had done their homework with the stock set-up for sure, and that’s how engines were cooled in those days before electric “everything”. All cars for decades now (including very high powered) use electric fan radiator cooling of course. Electrics fans usually use shrouds so can still pull air through the whole rad surface.
I was following a C8 when we were out the other week. It was a cool morning but the amount of heat coming out of the rear deck vents was surprising, distorting the view of the back of the car.

Drive a big block on a really hot day (so early/mid 30's C) with so much engine heat rising out ot the fender gills this is the potential image you'll see!

 

[teamzr1]

Do 1 or the other fans ever come on ?
Have you checked if the coils of relays are getting +12 volts with ign key on ?
Have 1 or 2 12 volt fuses ?
I assume the controller is controlling the coil with ground and OHM that to see if ground is present ?
Does the controller have some potometer to turn to adjust when fans come on, and if so, try changing the ON temp point ?

Do you know if relays are 4 or 5 pins ( normally open and/or also normally closed ) ?

As you mention, bypass the relay coils and jumper +12 volts to coil to the pin that is output to the fan(s)

If 5 pin, common design is

 

[teamzr1]

Not the best photo, but from what I see online with the SPAL dual fans, they seem to have two individual relays where I have this unit

Did your dad save all paperwork of history of car that might show what brand/model these electric fans are
that might show wiring schematic ?
Maybe find somewhere on whom the maker of this is and then search on internet for what install of wiring was

 

[Alex Gray]

Thank you all very much, what an awesome forum, within less than a day you’ve all helped me massively!!! I’ll get cracking and let you know!!! Legends

 

[Alex Gray]

Hi all, I’ve been doing a bit more fault finding.

Managed to get the relay box open, unfortunately no manufacturer or part no. to reference. Three relays in there.

On the signal wiring I have 6 as follows.

Single yellow, runs to the water pump
Grey and orange run to the temp sensor in the block, I assume this is two temperature set points?
Red and Green run into drivers section.
Black is to chassis ground.

In the other photo with my hand, I seem to have located a red wire with a spade connector floating suspiciously near the fuse box, I’m wondering perhaps if this is the ignition signal??

I’ve measured voltage across all wires with ignition on and have nothing so am assuming that’s my issue.

I must have knocked the wire with my foot.

Question, any ideas where I should reconnect that spade connector in the fuse board please??

 

[teamzr1]

That red wire going to the fuse box is what is needed for that controller
I assume what is needed is a fused circuit that is only hot when ign switch is turned on

So just for a test is jumper from that male spade to 12 volts of fuse panel after engine has heated up
and see if fans than turn on
If so, then find a female spade in the fuse box that is only hot when key is on

Question is what the 2 wires by dash are for, if for a on/off switch ?
Use a multi meter and see if either go to ground or 12 volts

 

[Forrest Gump]

There should be at least one spare terminal in the fuse box that you can go into, probably labelled "AUX"
The green wire that also goes through the firewall is quite likely to be a manual over-ride - is there a small switch anywhere? If it is then you don't need to wait for the engine to heat up to test the fans - just use that switch.
I'm not sure what the yellow wire is that runs to the water pump - they don't generally have a connection? can you put up a picture of that?
Those control units sometimes have a link to the air conditioning to switch on fans on when that is switched on.

 

[Alex Gray]

That red wire going to the fuse box is what is needed for that controller
I assume what is needed is a fused circuit that is only hot when ign switch is turned on

So just for a test is jumper from that male spade to 12 volts of fuse panel after engine has heated up
and see if fans than turn on
If so, then find a female spade in the fuse box that is only hot when key is on

Question is what the 2 wires by dash are for, if for a on/off switch ?
Use a multi meter and see if either go to ground or 12 volts

Thanks TeamZR1, I think you’re right, there’s an override in the cab that I need to find! I’ll be back tomorrow to take a look and hopefully get sorted!

 

[Alex Gray]

There should be at least one spare terminal in the fuse box that you can go into, probably labelled "AUX"
The green wire that also goes through the firewall is quite likely to be a manual over-ride - is there a small switch anywhere? If it is then you don't need to wait for the engine to heat up to test the fans - just use that switch.
I'm not sure what the yellow wire is that runs to the water pump - they don't generally have a connection? can you put up a picture of that?
Those control units sometimes have a link to the air conditioning to switch on fans on when that is switched on.

Cheers Forrest. I think I was wrong, it’s not the water pump and you’re right it’s on the air conditioner unit that’s driven by the belt.

Hopefully gonna get fans fixed tomorrow!!