Carb Cooling Fan - Wiring Help

[GA Architect]

If your fan draws less than three amp your configuration should be reliable. I will measure the operating current for the cooling fan tomorrow and let you know what it draws. If you look at the SPAL application notes, it does show the thermal switch as a low current input to their controller and the higher current for the fan motor is a separate output, similar to the VCM controller that you are using. Also the spec sheet for the VCM describes the 87 and 87a as 'a logical exclusive OR' (I would assume that there are pull-ups inside). Just saying.

Colonel,
I appreciate you taking your time to find the amperage that a carb fan draws. If it is much more than 3 amps, I'll remove and install my Klixon 1NT switch. The Klixon is rated for up to 25 amps, thus shouldn't be an issue. However, this sensor is a 150 degree on and 135 degree off. I would probably find another location to install it in lieu of attached to my exhaust manifold, as I have the SPAL currently installed.

As far as my wiring of the Waytek (In-Power) relay as I have it installed and being no electrical engineer, I took the directions & wiring diagram from a phone call I had with In-Power's technical department. That is the reason I used the diode and knowing where & how to install it. That phone conversation was more technical than an Good Ole County Boy from GA cared to know about relays.

(.....pull ups inside)? Too technical for me, went right over my head.

 

[ColonelMustardFJ40]

GA - Measured the carb cooling fan current draw today. For a few 100 milliseconds it draws 3.2 amps at start but then drops down to a safe 1.2 amps continuous. Bottom line is you should be good to go. Sorry about the delay getting back, but had family in for the weekend.

 

[Coolerman]

Question for whom ever has a working Cooling Fan system: What is the resistance of the thermo sensor when it is at its activation temp? Is it a dead short to ground or are there a few ohms of resistance? Reason I ask is I have a module that does not work on the bench when hooked to switched and always on power according to the schematic and grounding the thermo sensor wire. If I understand this circuit correctly, there is a relay that should engage and turn on the fan if the thermo sensor goes to ground while the engine is running, then run for about 20 minutes once the switched power is removed. I am checking the circuit board for cracks in any soldered joint, and all the diodes, caps and transistors next. Probably the electrolytic cap has dried up after 20 something years...

 

[GA Architect]

GA - Measured the carb cooling fan current draw today. For a few 100 milliseconds it draws 3.2 amps at start but then drops down to a safe 1.2 amps continuous. Bottom line is you should be good to go. Sorry about the delay getting back, but had family in for the weekend.

Colonel,
Thanks for the info. Makes me feel better about the system I've installed.

Now, on to the next project. Installing some new Procar Rally seats.

 

[78fj40mg]

I removed the carb fan heat sensor and the wire broke off the sensor. I'll be cleaning and re-soldering the sensor wire. However, is this a special rigid wire or can I use any wire for this purpose as this one doesn't seem to be in good condition.

In this pic the wire is still intact but was hanging off a single strand of wire.

 

[Coolerman]

Nothing special, just an 18ga wire and a couple of crimp on terminals.

 

[78fj40mg]

I refurbished and painted the carb fan sensor, installed new wire with heat shrink rated at 125 degrees C and new terminals ready for re-install

 

[GA Architect]

I refurbished and painted the carb fan sensor, installed new wire with heat shrink rated at 125 degrees C and new terminals ready for re-install

Nice work!

 

[unixman]

Question for whom ever has a working Cooling Fan system: What is the resistance of the thermo sensor when it is at its activation temp? Is it a dead short to ground or are there a few ohms of resistance?

I know this is a dated thread but... There really is no "activation temp" per se. You could use the same sensor in different models but change when the fan starts and stops by changing the controller. For a '78 Federal, the start temp is 100C which is about 2.7kΩ. There is no published curve that I could find, but the maintenance procedures list 2kΩ - 3.8kΩ for 90C - 110C as a passing test.

If I understand this circuit correctly, there is a relay that should engage and turn on the fan if the thermo sensor goes to ground while the engine is running, then run for about 20 minutes once the switched power is removed. I am checking the circuit board for cracks in any soldered joint, and all the diodes, caps and transistors next. Probably the electrolytic cap has dried up after 20 something years...

The relay closes when the ignition is switched off and the thermistor reports over 100C. The fan should not run while the engine is running. My '78 manual states it should run for no more than 30 minutes though it will open the relay if the temp falls below 85C (about 4.5kΩ).
The two parallel diodes in the corner of the board seemed to be a common fault in several boards I've seen.

 

[78fj40mg]

Y'all may want to read this thread: OEM Carb Fan Controller Replacement

 

[Solace in Solitude]

Y'all may want to read this thread: OEM Carb Fan Controller Replacement

That's @unixman's thread Mike - I think he read it

 

[78fj40mg]

That's @unixman's thread Mike - I think he read it

Oops! Thanks Danny! For some reason I thought it was Rick's thread.

 

[iptman]

I refurbished and painted the carb fan sensor, installed new wire with heat shrink rated at 125 degrees C and new terminals ready for re-install

Can someone show where this connects back in to the harness? My sensor wire broke off as well and I don't see any loose disconnected wires in the engine bay. I assume this eventually goes back to the controller behind the dash on the PS but I can't find the path.

Edit: Nevermind. I think my intake manifold is not original since I actually have this sensor on my truck too.

 

[78fj40mg]

Can someone show where this connects back in to the harness? My sensor wire broke off as well and I don't see any loose disconnected wires in the engine bay. I assume this eventually goes back to the controller behind the dash on the PS but I can't find the path.

It's the green wire bottom of pic.

 

[Fast Eddy]

The sensor you have is earlier. I can't speak for '77, but my '76 sensor is like that. It's a heat-activated switch, on or off. the later type is a thermistor with resistance corresponding to temp.

I swapped out my controller just yesterday and had some success, fan turned on when connected, then turned off when it cooled down. I'm going to say the jury is still out on my setup, but it was encouraging.

Edit: It has since come on once when it was hot. Jury is close to a verdict.

 

[iptman]

Mine's a July 77 CA spec so I imagine it's similar to yours. Should the fan only come on when the ignition is off and the temperature is above a certain threshold? I'm trying to figure out where to start troubleshooting since apparently I do have all the components in place.

 

[78fj40mg]

Mine's a July 77 CA spec so I imagine it's similar to yours. Should the fan only come on when the ignition is off and the temperature is above a certain threshold?

Yes, I have a '78 and that's how it operates.

 

[chuckost]

Mine's a July 77 CA spec so I imagine it's similar to yours. Should the fan only come on when the ignition is off and the temperature is above a certain threshold? I'm trying to figure out where to start troubleshooting since apparently I do have all the components in place.

Yes!

 

[chuckost]

$50 for a 20 minute timer switch? EBay has them under $20!

 

[Fast Eddy]

I'm trying to figure out where to start troubleshooting since apparently I do have all the components in place.

Put the sensor in boiling water connected to a multimeter. That sensor should be full open when room temp and full closed when hot. I'm not sure the actual temp, but boiling will do it.

If the sensor is good, check the fuse behind the heater duct by the carb fan controller. If that's good, open up the controller and look at the solder joints. Bad ones will show cracking and are easy to reflow with a soldering iron.

Checking the fan itself is easy. Hit it with 12v and see if it blows.

Even though you get past all those things, there are more mysterious issues, like connectors and PO wiring that could cause the system to malfunction.