DeWitts radiator install
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I set mine up so that one fan is on an engine temperature switch. When the AC is turned on, both fans run all the time. I've had no heat problems whatsoever in the Oklahoma summer heat, both on the highway and in city traffic. As Norm 1 said I would advise trying several configurations and see what works. With the 2 fans you have several options. Good luck, let us know how it works out!
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The 2 Spal fans that come on a Dewitts radiator are high amp fans. They move a lot of air and they draw a lot of current. When both of these fans come on together in parallel from a dead standstill there is a substantial draw on the vehicle's electrical system and you will always get the lights to dim, the blower to slow down, and usually the idle to decay momentarily on startup and you will also know when they release that load.
The right way is to have 2 temp switches. 10-20f apart. Like a 190f on and a 180f off for low speed operation and a 200f with a 190f off switch for the high speed. Or a 210 switch for high and 200 for low if you want to let the oil warm up to temp as it should.
Anyhow with 2 temp switches at slightly different temps we can mimic the C5 fan control seen in this diagram:
Instead of a control module looking at a variable temp sensor you will just wire the 2 fan switches to the fan relay control for low speed and high speed. Also A/C input can be wired to high speed relay control so that there is always a fan spinning when the A/C is on.
However the A/C control can be improved by adding a trinary switch from vintage air to the a/c system's high side. The trinary switch will shut down the compressor if it sees to high of pressure but also it will drive a fan relay based off of high side a/c pressure. This matters as it gives some level of adjustability to the a/c system for changing pressures within. The trinary switch can be had with an in line adapter from Summit Racing here:
Vintage Air 24678-VUS Vintage Air Trinary Switch Kits | Summit Racing
In a perfect world you would have 2 fan switches one mounted in the intake manifold and one in a cylinder head. Or one in each cylinder head, Or one in the intake and one in the water outlet. Or both in a water outlet. However you work that out. But 2 inputs controlling 3 fans in a way that brings them on in series and then breaks them out to parallel is the right control for the fans on your Dewitts radiator. And setup like this they will spend the majority of their time off or on low speed being nicer to your vehicle's charging system. And then the trinary switch fan control can just be spliced into the high speed relay.
It's the best you can do.
The right way is to have 2 temp switches. 10-20f apart. Like a 190f on and a 180f off for low speed operation and a 200f with a 190f off switch for the high speed. Or a 210 switch for high and 200 for low if you want to let the oil warm up to temp as it should.
Anyhow with 2 temp switches at slightly different temps we can mimic the C5 fan control seen in this diagram:
Instead of a control module looking at a variable temp sensor you will just wire the 2 fan switches to the fan relay control for low speed and high speed. Also A/C input can be wired to high speed relay control so that there is always a fan spinning when the A/C is on.
However the A/C control can be improved by adding a trinary switch from vintage air to the a/c system's high side. The trinary switch will shut down the compressor if it sees to high of pressure but also it will drive a fan relay based off of high side a/c pressure. This matters as it gives some level of adjustability to the a/c system for changing pressures within. The trinary switch can be had with an in line adapter from Summit Racing here:
Vintage Air 24678-VUS Vintage Air Trinary Switch Kits | Summit Racing
In a perfect world you would have 2 fan switches one mounted in the intake manifold and one in a cylinder head. Or one in each cylinder head, Or one in the intake and one in the water outlet. Or both in a water outlet. However you work that out. But 2 inputs controlling 3 fans in a way that brings them on in series and then breaks them out to parallel is the right control for the fans on your Dewitts radiator. And setup like this they will spend the majority of their time off or on low speed being nicer to your vehicle's charging system. And then the trinary switch fan control can just be spliced into the high speed relay.
It's the best you can do.
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4,990 Posts
In fact to keep it simple you could get this fan relay kit without a fan switch:
Amazon.com: Spal Fan Harness With Relay (40 Amp) : Automotive
Just get one of those. Then you can get 2 relay kits with the switches. Here is the one for low speed:
Amazon.com: Spal 185FH Cooling Fan Harness with Relay : Automotive
And this is the relay kit with the switch you will use for high speed:
Amazon.com: Spal 195FH Cooling Fan Harness with Relay : Automotive
One of each of the above will give you both switches, all 3 relays and even fuse holders and all needed wiring. And then get that trinary switch for better control over the A/C high side pressure.
Amazon.com: Spal Fan Harness With Relay (40 Amp) : Automotive
Just get one of those. Then you can get 2 relay kits with the switches. Here is the one for low speed:
Amazon.com: Spal 185FH Cooling Fan Harness with Relay : Automotive
And this is the relay kit with the switch you will use for high speed:
Amazon.com: Spal 195FH Cooling Fan Harness with Relay : Automotive
One of each of the above will give you both switches, all 3 relays and even fuse holders and all needed wiring. And then get that trinary switch for better control over the A/C high side pressure.
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4,990 Posts
I don't get the last post but he does make a point. For A/C control if you followed my diagram you will take the light green A/C compressor turn on wire from your vehicle's A/C control head and use that to turn on the high speed fan.
You do not need to get behind the A/C control head to do this. Under the hood at the accumulator you will have a low pressure switch. This switch has 2 wires. A light green and a dark green. Dark green is the power from the switch to the compressor. IF you use this dark green wire then your fans will cycle to the beat of your compressor. You need to take from the light green wire so the fans are more stable in there operation and just on when the A/C command is on.
Because this light green wire for the compressor is power and we need a ground signal from it to energize the fan relay we will need to use a relay to convert the power into a ground. A relay has 2 pins for the primary side or the coil. These are pins #85 and #86. You will wire one of these to ground and the other to the light green wire at the A/C low pressure switch.
Then for the secondary side you have pins 30(in), 87a(nc), and 87(no). You will wire pin 30 to ground and pin 87 will be tied into the blower high speed fan relay control or the dark blue wire in the diagram above.
This will bring on just one fan in high speed if the motor is cold and if the motor is warm and the low speed fans are on this will break them out to both fans at high speed. This is a very correct method of setting up fan control for A/C functions. It could be a little bit better if instead of just tying the high speed fan to A/C on command we were to regulate the pressure drop that comes with the fans off of pressure in the A/C system on the high side. And we can achieve that with a trinary switch from Vintage Air. Vintage Air 24678-VUS Vintage Air Trinary Switch Kits | Summit Racing
You do not need to get behind the A/C control head to do this. Under the hood at the accumulator you will have a low pressure switch. This switch has 2 wires. A light green and a dark green. Dark green is the power from the switch to the compressor. IF you use this dark green wire then your fans will cycle to the beat of your compressor. You need to take from the light green wire so the fans are more stable in there operation and just on when the A/C command is on.
Because this light green wire for the compressor is power and we need a ground signal from it to energize the fan relay we will need to use a relay to convert the power into a ground. A relay has 2 pins for the primary side or the coil. These are pins #85 and #86. You will wire one of these to ground and the other to the light green wire at the A/C low pressure switch.
Then for the secondary side you have pins 30(in), 87a(nc), and 87(no). You will wire pin 30 to ground and pin 87 will be tied into the blower high speed fan relay control or the dark blue wire in the diagram above.
This will bring on just one fan in high speed if the motor is cold and if the motor is warm and the low speed fans are on this will break them out to both fans at high speed. This is a very correct method of setting up fan control for A/C functions. It could be a little bit better if instead of just tying the high speed fan to A/C on command we were to regulate the pressure drop that comes with the fans off of pressure in the A/C system on the high side. And we can achieve that with a trinary switch from Vintage Air. Vintage Air 24678-VUS Vintage Air Trinary Switch Kits | Summit Racing
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