Belt-driven to Electric Fan Conversion Guide

It's inevitable that i will convert to electric fan if i am going to put 4A-GE Smallport in. First, smallports never did come with belt-driven fan. Second, even if i insist to put such fan on the waterpump pulley, the pump was not designed to hold the extra weight and its lifetime would be significantly reduced.

I consider this as the best time for me to write about this as a fellow Charmant lover, Wahyu, just finished similar conversion on his stock 4A-C. Most of the pics are taken from his blog. I am just translating to English what Wahyu has written in his blog and added some of my experience.

If you're using the stock Charmant radiator (and i hope i'll be able to keep it too for the conversion), one of the best fitting electric fan as claimed by Wahyu is from Suzuki Karimun, our local name for Suzuki Wagon R. Here's how it looks.

Look, eleven blades! That's a lot of blades!

Wahyu seems to have done his homework in determining the fan with the best dimension for Charmant's radiator. Here's how it looks fitted after some minor welding to make the fan mounting brackets.

Looks stock! Job well done there Wahyu..

Believe it or not, deciding where and how to mount the fan to the radiator is the easy part. The hardest part comes from the wiring. There are few ways to wire your new electric fan depending on how properly you want to control the fan.

Before i get to the wiring, i'd like to say a thing about relays. Relays are basically current controlled switches. Whenever you need to drive large current device(s) with only small driving current available, relay should always be in the equation.

In simple terms, if you flow direct current from pin 85 to 86 (or the other way around, doesn't matter), you'll induce electromagnetic force from the coil inside which in turn pulls the switch blade and connects pin 87 to 30.

It's surprising that such simple component is often misunderstood, even by mechanics with years of experience in their pocket. I dare to say that because i met one when i did similar conversion on my previous ride. I end up doing the wiring myself. I am not saying that i know everything about relays but i sure know more than said mechanic. Anyway, read on and you'll see what i mean.

Now i'll get back to the wiring topic. First is the simplest manual fan control. You only need a toggle switch and a relay for this. Here's my illustration on how to wire it.

With Wiring A, you have total control of the fan. When you see the engine temperature too high, turn the fan on. When it's too cold, turn it off. Since humans are prone to errors, this method can be dangerous. You might forget to turn on the fan and overheat your engine or on the contrary, forget to turn it off and you'll be running your car at sub-ideal temperatures and replacing carbon brushes on your fan motor too early.

Anyway, all of the wiring i am going to show you, they will always be driven from IGN or Ignition signal. This ensures that if you kill your engine, you won't drain your battery with the fan running. If you wish to allow the fan to run although the engine's off, you know what to do. If you don't, you shouldn't even be doing the wiring..

With said risk of Wiring A, we improve it a bit to Wiring B and replace the manual switch with thermoswitch.

A thermoswitch is controlled by temperature. For Wiring B, you'll need what we call a "normally-open" thermoswitch or N.O Thermoswitch. An N.O Thermoswitch at room temperature switches off while at temps higher than certain threshold will switch on. The threshold is set from the factory and varies between 70-90 degrees Celcius. This threshold determines at what temperature your fan turns on, so choose your thermoswitch carefully. I'd say threshold between 88-92 degrees is good but don't quote me on this. Usually the threshold value is written on the thermoswitch.

Any car that uses electric fan should have a thermoswitch. This is how they look.

The flat surface is the one that reads temperature and it should be exposed to environment at temperature as close as possible to the engine. Usually the easiest way is to tap into your radiator hose and let the switch read from the heated water. Be careful that you should always tap to the hose that flows water INTO the radiator and not OUT OF it. Water that comes out of the radiator is at lower temperature than the engine and you should always tap into temperature as close as engine temp. Here's an idea how to do it.

As said above, you need N.O Thermoswitch for Wiring B. However, most probably you'll encounter the "normally-closed", N.C Thermoswitch as i believe this is what the majority use. This works the opposite way the N.O does. At temperatures below set threshold, it switches on while at higher temps, it switches off. This would not work on Wiring B as you would constantly turn on the fan since the engine would never reach the threshold temperature. Or if it does, it gets even messier since now the fan would turn off and the engine just gets hotter. So here's a warning: NEVER use N.C Thermoswitch on Wiring B.

I believe some of us are still under the impression that all thermoswitches are normally open. Same applies to the mechanic i told you above. He wired it as wiring B and smiled like nothing's wrong when he saw the fan turn on at sub-threshold temp. We argued and, as i said, i end up doing the wiring myself.

Here's the wiring when you have N.C Thermoswitch, Wiring C. You'll need one more relay with an extra pin called 87a, usually called 5-pin relay.

It you wire it the way Wiring C goes, your fan would turn off no matter what the engine temperature is when you turn off your engine. However, if you want to save a relay and keep the fan turning until your engine cools although you've turned off the engine, you can skip the relay marked inside blue box and connect the fuse directly to the thermoswitch (make a jumper from where pin 87 and 30 of first relay used to be).

If you're curious about relays, you can read some more here. However, here's a 5 pin relay diagram.

On normal condition, where you don't flow current from pin 85 to 86, pin 30 is connected to pin 87a. Once you flow current to pin 85-86, pin 30 is disconnected from 87a and connected to 87 instead. So on normal condition, pin 87a is connected. Ring any bell? Yes, pin 87a is called "NORMALLY-closed" while pin 87 is "normally-open" switches! Your usual 4 pin relay is basically 5 pin relay without pin 87a.

A thing about normally-closed thermoswitch, why do they exist anyway? From what i know, they are designed as a safety measure against fault. Let's say if you use Wiring B and a normally-open thermoswitch, what happens if due to aging or any other cause, the switch fails to connect? Your fan would never turn on, right? Next thing you know, you blow your engine because of one tiny fault in your thermoswitch. That's why they come up with normally-closed thermoswitch. In the case your N.C fails to connect, you can still run your car since the fan is now on "always ON" mode due to the fail on the switch! Then you might ask what happens if your N.C Thermoswitch fails to disconnect as the same mess would happen, the fan fails to turn on. I guess the answer is that "failure to connect" is more probable than "failure to disconnect". I believe, N.C thermoswitches are more common now than N.O due to said advantage.

If a guy hands you a thermoswitch, how do you determine its N.O or N.C? That's easy. Get an ohm-meter, make sure the switch is at room temperature and measure the resistance on the pins. If its infinity, then its N.O and if its close to zero, then it's N.C. Careful if you find any value in between (tens to thousands of ohms), it might not be a thermoswitch after all as you might be testing a thermosensor. Blow some air to the "thermoswitch" to slightly cool it and see if the resistance changes, if it does, then you can be sure that you're holding a thermosensor.

Here are some tables to summarize what i've been blabbering about thermoswitches and relays.

THERMOSWITCH


5-PIN RELAY


Oh i almost forgot. If possible, get a dual-speed electric fan. Connect one wire like on the wiring diagrams above and connect the other one to your air-con or a manual switch. If you connect it to the latter, you can manually increase fan speed if the normal speed is not enough to cool off your engine.