Hi Folks.

Recently I had a need to take control of the electric fans in my VR Commodore.
The operation of the engine cooling fans had always been erratic. A couple of days ago, the cooling fans came on when the car was started at 5am to go to work. It was not the first time this has happened. Usually, the fans come on only when the temperature gauge reaches Volcanic.

Various things have been replaced as well as fitting a thematic sensor/controller. Results still erratic. So, time to monitor and take control. I wanted to monitor the control line from the ECU, (electronic control unit), to the fan driver relay, and also, when the fans were actually on.

I used a red led to indicate engine hot and fans running, and a green led to monitor the state of the ECU output.

What I did was to add the two led's to the lines being monitored, and a switch to ground the ECU output. This would let me override the ECU. Then, I remembered that I have a couple of dozen universal timers lying around. Brainwave. I fitted a programmable timer to the panel with the leds and now have a three position switch which allows 1. Auto operation (prayer). 2. Fans on. And 3. Timer. This I set to three minutes, reset-able, to to give a bit of hysteresis.

Normal operation is to monitor the temperature gauge, with the switch set to Auto, and pray that the ECU works properly. If the temperature climbs too high I can switch the selector from auto to timer momentarily, then back to auto to trigger the timer.
The On position, will run the fans continuously. Excellent when caught in a traffic jam outside the Panther's home ground on a game night.

This post was meant to be about switch types, but the back ground story got a bit out of hand. Anyway, this might be useful to others now that Summer is approaching. I will get back on topic soon.

Wayne.

Used to have issues with fan control relays back in the days when we had a fleet of Commodores. Sticking contacts, N/C contacts.

My son is restoring an HQ ute. 5 litre V8 to which we added a heavy duty radiator and cooling fans. We bought a very nice programmable device that measures the radiator core temp. Works well.

I have a VY Commodore, which has a similar fan arrangement to the ealier VR, which I also once had. As far as I can remember the fans work in response to both the coolant temperature and whether the air conditioning is on or not. One thing you don't want to do is prevent the fans from running when the condenser coil for the air conditioning is too hot. Your air conditioning will trip on high head pressure and a continuance of that scenario will damage your compressor.

If you are on a motorway at 110km/h the fans will probably be turned off as they would restrict airflow when turned on whilst at that speed. The volume of air coming through the grille and bumper would be sufficient to keep things cool at that speed, perhaps with the exception of 40+ degree days.

I miss my old VR wagon. It was a six seater with a column shifter. Lots of room to stretch the legs when on the open road. It's a shame they don't build cars like that anymore.

This topic awakened a memory.

We have a Pontiac Screaming Chicken "Knight Rider" model with a 350 Chev small block.
Back in around Y2000 we had overheating difficulties that were ultimately addressed by refurbishing the heads (blocked passages) and paying attention to the airflow to the heat exchangers
The car has no front grille intake as such (the nose is blank). Air is picked up under the front chin and hopefully turned at 90deg by a deflector ( which was missing) to turn 90 deg again to go through the radiator, gearbox exchanger etc.
Anyway, we were stuffing bigger and bigger electric fans into the thing and needed some sort of controller for the three fans involved.

The block temperature sender gave an analogue voltage gradient to run the dash temp gauge so I picked that signal and on the back of an envelope drew up a circuit to sense that and at top speed "designed" a controller in a jiffy box that drove relays to run each fan in response to rising temp.
Great laughter all around, we christened it the "Fan-o-Matic XLS 5000" and I whipped the thing up, wired it in, and amazing its now 22 years later and it has not missed a beat. This back of the envelope scribble is the only drawing ever made! I grabbed a quad op-amp some BC107's, led's, trim pots, diodes, a scrap of veroboard made it up stuck it in a jiffy box with little holes to adjust the trim pots stuck it in and away we went. The relays are in the relay bank external to the box.
The engine has gone through a few changes since then, there are only two big fans now from a Ford car of some breed but the little box just sits there and works.
I am amazed that nothing has failed seeing how rough the build was, proving what a great design engineer I am!!!!!

I'll send Brad a jpg of the back or envelope design and you can have a laugh.

Fred.

Fan O Matic Circuit Diagram

You didn't have a gas turbine in it like KITT had?

No Brad, no turbine, just a big lazy cast iron lump that goes on for ever and ever.
On a long road it just keeps accelerating until you run out of road or courage!
A Toyota Corola can ace it off the line up to 100Kmph, but then the Ponty just settles down and keeps going.
No competition for a modern Chev or Ford but back in 1980 an amazing cheap yank car.
Fred.

Document uploaded to Post 4.