OK. Here is the info that was posted in another forum here in Oz. Note that the numbers are based on a local car, the VY Holden Commodore (GM Holden), but the end result and the basis will be the same.
Sorry for the long post, but heaps of info.
Cheers
Michael B
I am waiting on some info from the HVAC dude, but I got some interesting stats regarding the temps at what you switch on the fans at. Largely they back up previous numbers quoted in other discussions, but basically the values are such.
For fans running single speed (twins or singles) : Aim for a “temp on” temperature about 10 degrees above thermostat open, and a ”temp off” temperature of 5 degrees above the thermostat temp. This way, you allow for hysteresis of the various temp controlled items, and you also don’t end up with the fans and the thermostat fighting each other at a switch over temp.
For fans running twin speed (twins thermo’s ala AU Ford etc) : The basic set-up is to have the fans run in two modes – Low power and High power. This can be done in a few ways, but the Ford and Holden version is similar (I’m waiting to get the cct details so that I can share this info). The low power setting involves running the two fans together in series which means that both fans only see 6V and therefore only give about 35% of their cooling capacity. With the fans run in parallel, both see 12V, and give 100% cooling capacity.
The switch set-up is that you either run two switches or use a switch that has both internal contacts in it (apparently the JD Vectra has this set-up as do others). For a thermostat of 90 degrees, the low power switch would have the same temps as listed above (fans on at 10 deg above thermostat, and off at 5 deg above thermostat), and for the high power setting, you would have an on temp of 110 degrees and off at 105 degrees, and this allows for a 5 degree hysteresis once again.
The High/Low power set-up is best for DD cars, whilst if the car is an occasional fanger, it is not so important. Part of the main basis for the high/low fan speeds is that when the temps rise and the fans switch on, the engine doesn’t see a huge slug of cold(er) water and then shut the thermostat and you end up with a bit of temperature hunting, but instead you get a gradual cooling that keeps the temperature much more stable.
Inst. Cluster "Hot Chime" at 118 degC
VY V6 A/C Clutch: "Cut Out" 119
"Cut In" 115
VY V6 Rad Fan Temps: "Low Fan" ON= 104 OFF= 99.5
"High Fan" ON= 107 OFF= 103
VY V6 Thermostat Temps: "Nominal" 91 degC
"Fully Open" 104 degC
And now, here is a cct for high low fan speed setups that has been modified to suit mechanical switches. It was used by Ford for their Bosch fans up to BA, and similar to VE.
Some other comments from the guy ;
It requires 3 relays in total, I've shown the P/N's for Holden VY/VZ fan relays which are well suited to fan motor loads. You need good quality high current relays, terminals & cable for cooling fans as they suck a lot of current (typically 20 amps per motor) & can burn wires/terminals or loose fan performance due to voltage drop. Also, you often need to upgrade your Alternator when you fit Electric Cooling Fans, people usually overlook this. Additionally, make sure that there is absolutely no electrical connection to the coolant circuit through your fan wiring as this can cause severe corrosion of the cooling system parts. Basically, this means the temp switches & fan motors must not ground through the radiator or coolant, they should be electrically isolated from the coolant, hoses & radiator.
