There are a couple of reasons why you might need an electric radiator fan temp trigger. You could have needed a cooling system upgrade and have sourced a bare fan from a wrecker, installed it – and then wondered how you’re going to have it automatically turn on and off.
Or the temp switch in your current car’s cooling system may have failed – and you’re not too rapt with the cost of a genuine replacement. (And plus it’d be nice to have a bit of control over when the fan actually comes on, too.) Or maybe you’ve replaced the radiator with an upsized design which turns out can’t take the original rad’s temp switch. Of course, there are lots of solutions – commercially available adjustable radiator temperature switches (eg see ) or even the DIY adjustable temp switches we covered in. But the approach in this story has significant advantages over those other techniques. Firstly, it’s easy to alter the temp at which the fans will cut in. In fact, you just turn a ‘pot’ (potentiometer) on the circuit board. Secondly, you can adjust that point very finely indeed – in some systems, to the individual degree Celsius.
Thirdly, the temperature at which the fan switches off again (ie the hysteresis – the difference between the switch-on and switch-off temps) is also adjustable. And finally – and this is a killer – you don’t need to install a new temperature sensor. Instead you can take the temp signal straight off the engine management ECU.
The approach uses the Simple Voltage Switch kit developed by Silicon Chip electronics magazine. The kit – and the book in which it is featured – are available from the AutoSpeed Shop and Jaycar stores. So how does the system work?
Well, the ECU sends out a regulated voltage to its coolant temperature sensor, which is a device that changes in resistance with temperature. If the resistance is low, the ECU sensor voltage is pulled lower.
If the resistance is high, the ECU sensor voltage stays higher. Since most sensors have a resistance that gets lower as the temperature gets higher, the voltage sensed by the ECU gets lower with increasing temp. Say all that through twice really fast! But hey, you don’t need to worry about any of that anyway. All that you really need to know is that one of the wires connecting to the ECU’s temp sensor has a voltage on it that gets lower as the coolant temp gets higher. The Simple Voltage Switch (SVS) continually monitors the voltage on this wire, tripping when it falls to a level that you’ve pre-set.
In turn that switches on the radiator fan. When the coolant temp again falls (and so the voltage rises), the SVS switches the fan off. A red LED on the SVS shows whether it’s in its tripped state or off.
Fitting and Set-Up In this case the guinea pig car was a 1988 Maxima V6 Turbo with twin factory fitted electric fans. A change in radiator meant that the original temp switches could no longer be used.
The first step in the installation is to back-probe the connections to the coolant temp sensor, either at the ECU or near the sensor itself. (On the Maxima we did it near the sensor because it was quicker and easier to find the right wire without having a dedicated workshop manual). As mentioned, you’re looking for a voltage (normally between 0-5V) that decreases as the car warms up. So you can easily see this change, start off the measuring process with the engine cold.
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Here the voltage shown on the meter is 2.369V – it was falling rapidly as the car warmed up. Once you’ve found the right signal wire, solder a new wire to it and then run it back into the cabin. The next step is to build the kit and test that it works. As mentioned, in this application the kit needs to be configured to trip on a falling voltage.
This requires that during the build process a diode is orientated in a specific direction and a moveable link placed correctly. Follow the kit instructions carefully – in fact unless you are an experienced electronics kit builder, we suggest that you buy the built and tested version (although note a link will need to be moved and a diode orientation swapped, as the pre-built version is configured to switch as the signal voltage rises). The next step is to install the module in the car. Connect 12V and earth wires correctly, and connect to the SVS signal input the wire that you’ve run to the coolant temp sensor. (Note that the SVS won’t cause any additional load on this output – the rest of the EFI system will keep working happily.) At this stage you don’t need to connect up the fan, although as shown here you can put in a pilot light if you can’t see the SVS’s indicator LED. Turn the hysteresis pot fully anticlockwise, then start the car and turn the voltage adjustment pot until the SVS’s LED comes on.
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If you had the radiator fan connected, it would be on now too. Let the car warm up and then adjust the pot until the SVS just turns off. That is, you’ve set the SVS so if the car gets any warmer, the LED will come on. With the hysteresis pot set to its minimum (ie fully anticlockwise), the LED will go off quickly once the temp starts to drop. If the LED goes off too early, adjust this pot a little clockwise. Note that the set-up process can require some trial-and-error changes, so leave the pots accessible for a day or two of normal driving so that the fine-tuning of the switch behaviour can be adjusted.
Make sure that you don’t set the temp threshold too low or the fans will be on all the time – in most cars you want them trip when the temp needle gets to say 60 or 65 per cent of full movement. Well, over half way, anyway. Connecting the Fan. The next step is to connect up the fan. While the SVS has an existing on-board relay, all radiator fans should be driven using a separate, heavy duty automotive relay. Connect it up as shown here.
If the SVS is being used to replace an existing temp switch, you can use the relay that probably already exists in the car’s wiring. In that case, just wire the NO (normally open) and COM (common) terminals of the SVS’s relay to the connections that previously led to the temp switch. In fact, that’s exactly what we did on the Maxima, an approach which saved having to buy a new relay and run all its associated wiring. More of our most popular articles. 4 March, 2008 Making Your Own Bio-Diesel - 30 June, 2009 The NS Savannah - 4 May, 2010 Ride Quality, Part 1 - 21 August, 2012 Detonation and Pre-Ignition - 28 May, 2004 Undertrays, Spoilers & Bonnet Vents, Part 1 - 21 February, 2006 Making Things, Part 1 - 2 October, 2012 Mounting big driving lights, Part 1 - 22 November, 2003 Revisited: The GM Concept Cars - 21 October, 2014 Powdercoating of fabricated parts - 30 September, 2008 Building a Home Workshop, Part 8.
By If your vehicle has been overheating or doesn’t warm up properly, you may need to replace your thermostat. If the thermostat sticks in the open position, it doesn’t keep the liquid in the engine long enough, so you have trouble getting your car warmed up. If the thermostat sticks in the closed position, the liquid isn’t allowed to get to the radiator, and overheating results. Office 2010 crack. Because replacing the thermostat is quite simple and thermostats are quite inexpensive, you may want to try this task before you take more drastic measures. Just be sure that you do this when your engine is completely cooled.
Thermo Fan Switch
Due to the high current draw of a thermo fan you'll need to run its 12-volt power supply through a relay. You'll also need a method of switching the fan on and off at certain coolant temperatures and, of course, only when the ignition is on.
There are a number of ways to achieve this, but one of the easiest is to buy a Davies Craig Thermal Switch kit. These kits retail for around AUD$80 and include the necessary relay, an adjustable temperature switch, mounting bracket and a complete wiring loom including terminals and a fuse holder. Note that this kit dates back a few years so you might be lucky enough to find a second-hand one at the wreckers when you're looking for the thermo fan. The relay's 12-volt supply can come straight off the battery but make sure the supplied fuse holder is mounted close to the positive post to ensure maximum safety.
The relay's earth can be either the battery's negative post or a reliable body earthing point. Note that the earth lead from the thermo fan can share the same earthing point as the relay - this makes installation easy. Wiring the thermo fan's switched input requires a bit more effort. Find an existing wire under the dash that is switched on and off by the ignition (such as the switched power supply to the radio) and use the supplied scotchblock terminal to T in another wire. This new wire should then be connected to one of the terminals of the adjustable temperature switch mechanism. The second terminal of the switch mechanism should then be wired to the relay.
(Note that the pins of the relay are clearly identified in the Davies Craig installation instructions) This arrangement means the fan will activate only when the ignition is on and the coolant temperature switch has been tripped. The last step of the installation is to insert the appropriate spade fuse into the fuse holder. In the case of a 12-inch thermo fan (such as ours) you'll generally need a 20-amp fuse, while less powerful fans use smaller fuses.
Due to the high current draw of a thermo fan you'll need to run its 12-volt power supply through a relay. You'll also need a method of switching the fan on and off at certain coolant temperatures and, of course, only when the ignition is on. There are a number of ways to achieve this, but one of the easiest is to buy a Davies Craig Thermal Switch kit. These kits retail for around AUD$80 and include the necessary relay, an adjustable temperature switch, mounting bracket and a complete wiring loom including terminals and a fuse holder. Note that this kit dates back a few years so you might be lucky enough to find a second-hand one at the wreckers when you're looking for the thermo fan. The relay's 12-volt supply can come straight off the battery but make sure the supplied fuse holder is mounted close to the positive post to ensure maximum safety. The relay's earth can be either the battery's negative post or a reliable body earthing point.
Note that the earth lead from the thermo fan can share the same earthing point as the relay - this makes installation easy. Wiring the thermo fan's switched input requires a bit more effort. Find an existing wire under the dash that is switched on and off by the ignition (such as the switched power supply to the radio) and use the supplied scotchblock terminal to T in another wire. This new wire should then be connected to one of the terminals of the adjustable temperature switch mechanism. The second terminal of the switch mechanism should then be wired to the relay. (Note that the pins of the relay are clearly identified in the Davies Craig installation instructions) This arrangement means the fan will activate only when the ignition is on and the coolant temperature switch has been tripped.
The last step of the installation is to insert the appropriate spade fuse into the fuse holder. In the case of a 12-inch thermo fan (such as ours) you'll generally need a 20-amp fuse, while less powerful fans use smaller fuses.
The Pacet electric cooling fan is available in two sizes; which you need depends on the size of your engine. The smaller fan (A) comes ready assembled with the motor in its support bracket. The larger fan (B), has first to be assembled, using support brackets (C) and motor (D). Both kits are supplied with a thermal sensor and switch with mounting bracket (E).
To secure the fan to the radiator you use the special ties, washers, sponge pads and nuts (F). Extra wiring and terminal connectors with an in-line fuse (G) are supplied to wire the fan up. All cars have a fan to help cool the coolant as it passes through the radiator. On most cars, the fan is driven directly by the engine, usually via the generator drive belt. But this arrangement means that the fan always runs at the same speed as the engine. This has several disadvantages.
How To Install A Thermo Coupler For Furnace
Mechanical problems First, the fan runs as soon as the engine is switched on and is cold. This is when the engine needs to warm up as soon as possible for maximum efficiency, and having the fan running delays this process. Second, when the car is travelling fast and the engine is running at high speed, the fan is also turning over at its fastest. But in these conditions, the airflow through the radiator is enough to keep the engine cool, so the fan is being driven for no reason - all it is doing is wasting power.
Third, in a traffic jam, when the engine is idling and the car is stationary, there is no proper airflow through the radiator and so the engine can easily overheat. Yet, because the engine is idling, the fan is also running at its slowest and often cannot keep the engine cool enough.
Electric fans The solution is to fit an electric fan driven by a motor. The fan is switched on and off by means of a thermostatic sensor switch fitted to the cooling system. When the temperature of the coolant rises to a certain point, the sensor switches on the fan. The fan then operates until the temperature falls below the critical point, when the sensor switches off the fan.
The electric fan keeps the engine much nearer its optimum running temperature, saving fuel and gaining engine power. Details of fitting an electric cooling fan differ for front-wheel-drive and rear-wheel-drive engines.
This sheet looks at rear-wheel drive fans. The other type will be covered in a later Projects sheet. Fitting an electric fan.
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