Another thread on carb fan. Have trouble shot everything help

Joined
Dec 31, 2020
Messages
57
Location
gig harbor
So. 1978 Fj 40. Bone stock motor/carb still has smog equip etc. does have new radiator and hoses

Carb fan will not come on. I have read ALL the threads and have done the following:

1 cleaned and inspected all connections from temp sensor to fan and all points in between
2 checked the in line fuse on passenger side firewall. It was the original fuse. It was blown. Replaced it
3 took carb fan module apart and inspected all solder joints. Looks as new ( it is a very clean FJ under the dash and wiring )
4 pulled the switch off of the fan and hooked it direct to battery. Fans runs strong and fine when direct wired

I’m out of options. Ideas ?

now I do live the the pacific NW. it does not get very hot here although it will be 100+ for the next few days ( very unusual here). So I did read that it simply might not be getting hot enough to activate. I had a 79 and it did not matter if it was 60 degrees and raining. That fan came on every time when I drove the rig and ran for several minutes after shutting it off.

is there a way to manually activate at the sensor to ensure wiring is all good and it is just not getting hot enough? Take sensor out and heat it with a lighter? Manually ground it to activate? I’m out of answers

thanks in advance
 

Ming89FJ62

Pig farmer extraordinaire
GOLD Star
Joined
Jul 31, 2002
Messages
1,716
Location
Palatine, IL
If everything is in working condition you should be able to ground the wire to the thermo couple near the exhaust manifold and the fan should come on after you turn the key off. If that doesn’t do it I’d suspect your controller is bad. They regularly pop up on bay.

if that works then you know the sensor is bad. If not suspect the controller.
 
Joined
Dec 31, 2020
Messages
57
Location
gig harbor
If everything is in working condition you should be able to ground the wire to the thermo couple near the exhaust manifold and the fan should come on after you turn the key off. If that doesn’t do it I’d suspect your controller is bad. They regularly pop up on bay.
Can you tell me how to manually ground it ?

should I unscrew it from manifold and run a wire from the sensor tip to ground or?.?.
 
Joined
Oct 7, 2011
Messages
1,108
Location
Austin TX
Ground the wire that is attached to the sensor. The sensor is just a snap switch. When it reaches about 160 degrees it grounds the (blue??) wire. Not sure and it is late, but I think the wire is blue. I don't see in your prior work that you verified the little can relay is good. If you ground the sensor (snap switch) wire and the fan doesn't come on, it could very likely be the can relay. It is in close proximity to the controller box. Relays are readily available from more modern versions of Toyotas. Just look up the number on the side of the relay on Ebay.
 

Ming89FJ62

Pig farmer extraordinaire
GOLD Star
Joined
Jul 31, 2002
Messages
1,716
Location
Palatine, IL
Can you tell me how to manually ground it ?

should I unscrew it from manifold and run a wire from the sensor tip to ground or?.?.
Grab a small piece of wire, gauge really doesn’t matter, and attach to the stud on the back of the temp sensor (alligator clip makes it easy) then attach to a ground on the frame.
 
Joined
Dec 31, 2020
Messages
57
Location
gig harbor
Grab a small piece of wire, gauge really doesn’t matter, and attach to the stud on the back of the temp sensor (alligator clip makes it easy) then attach to a ground on the frame.
Ok. I did this. Still no fan and when I grounded the sensor with the wire loom still attached I saw the temp gauge on the cluster spike to H so that is working

where is the relay Doug Austin tx spoke of? Pic or exact location ?
 

imyahucklbrry

“In Vino Veritas”
SILVER Star
Joined
Jan 29, 2014
Messages
1,565
Location
GA - As close to the lake as I can afford...
Think this is the relay that is referenced…
3268A58D-9128-4AFE-AD99-5463B7F88F61.jpeg
 
Joined
Oct 30, 2007
Messages
10,417
Location
Plano texas
Hi, Grounding should start the motor when the engine is turned off,it will run for about 30 minutes. Mike
 
Joined
Jan 17, 2005
Messages
6,390
Location
Southern Colorado
My '78 cooling fan had been hot-wired to run on a manual switch, but they did not disconnect the 'fan computer' when they did so. So, a diode in the fan computer was fried, and I replaced it with a zener diode from Radio Shack, and the controller worked for another 25 years before dying completely.

So, even if the solder joints on the fan computer board look good, look for black marks on the circuit board around the diodes, in case they are fried. I see fan computers for sale at times on Mud, so that is another option.
 
Joined
Dec 31, 2020
Messages
57
Location
gig harbor
Ok. Confession time. Up until yesterday I was focusing on the temp therm sensor screwed into the manifold thinking it was the carb fan sensor. ( man the connections there are clean and working !)

I know. I’m dumb. I should know better. Regardless I was correct on the blown fuse and controller and the condition of both.

Tonight I found the correct carb temp sensor under the carb ( thank you members). The wire was cut at the sensor. Found the remaning wire in the loom along side the brake controllers and carb wires. That wire is blue per Coand diagram. ( again. Many thanks ). Got super excited as I was sure this was the issue

re wired new wire to carb temp sensor and went for a drive. ( it’s 109 degrees here today). No dice. Fan would not turn on

I grounded it. Again. No dice

WTH??
 
Joined
Oct 7, 2011
Messages
1,108
Location
Austin TX
Buy a relay. That might fix it. Also go over the circuit board with a magnifying glass and look for broken or cracked traces. I see in your original post that you replaced a fuse on the passenger side firewall. My '79 had the controller under the dash just to the right of the steering column. Was the fuse that you changed wrapped in yellow electrical tape? Could you post a photo of your circuit board (both sides)?
 
Joined
Dec 31, 2020
Messages
57
Location
gig harbor
Yes. Fuse was wrapped in yellow tape. Was an original fuse. Was directly next to the controller box. I will remove and take pics of the box tonight
 

Engineer8000

CAPE FEAR ELECTRONICS
SILVER Star
Joined
Aug 16, 2019
Messages
1,479
Location
SOUTHPORT NC
Website
forum.ih8mud.com
Looks like that if you can find the relay and ground pin 3 (GY wire), the fan should run. That will determine if the relay is the problem.
 

Engineer8000

CAPE FEAR ELECTRONICS
SILVER Star
Joined
Aug 16, 2019
Messages
1,479
Location
SOUTHPORT NC
Website
forum.ih8mud.com
Looking through the wiring diagrams on @Coolerman web site, it looks like the cooling fan relay was added in 79 so you may not have one. Also, the temperature sensor is drawn as a thermistor vs. a switch. I have a 85927-60040 here that I'm looking at, it has the T2333 ic in it that works with the thermistor in the AC amplifier. I don't know that grounding the wire to the sensor will tell the controller to turn the fan on since it is looking for a particular resistance. Does anyone have experience with that? Does your controler have that T2333 ic in it? Also if it has a relay in it, you most likely don't have an external relay.
 

Ming89FJ62

Pig farmer extraordinaire
GOLD Star
Joined
Jul 31, 2002
Messages
1,716
Location
Palatine, IL
Looks like that if you can find the relay and ground pin 3 (GY wire), the fan should run. That will determine if the relay is the problem.
Note of clarification - GY designates Green wire with Yellow trace on it. Not Gray

Carry on
 
Joined
Oct 7, 2011
Messages
1,108
Location
Austin TX
If Engineer8000 is correct, and I have no reason to doubt him, then there was a substantial change in the design of the fan circuit between 1978 and 1979. My '79 definitely has an external can type relay (not attached to the circuit board), and mine also definitely has a snap (on/off) switch at the manifold, as opposed to a thermistor.
So, if your truck uses the thermistor type sensor, he is absolutely correct that grounding the blue wire will NOT turn on the fan. You can use a multi-meter set on ohms to check the resistance of the thermistor when it is cold versus when you stop the truck after a 20 minute ride. If you get a resistance reading of anything much over 1 ohm when hot, then you have a thermistor. A snap type sensor would be open when cold (no reading), and pretty much a direct short to ground when hot.
 

Users who are viewing this thread

Top Bottom