ryeguy2006a

iTrader: (27)

So, I'm getting ready to do an efan swap on my LS Swapped OBS Silverado and thinking about doing exactly what you are posting here, but taking the 12v signal from the AC clutch and using a relay convert to a ground signal. I just came across this diagram and am curious if you or anyone here has done this?

Thanks,
Ryan

hookemdevils22

iTrader: (12)

You'd simply connect the 12v signal input to 85 and a ground to 86 for control. Connect another ground to 30 and 87 to the yellow wire in the schematic above. 12v comes on, energizes the coil within the relay and closes the 30-87 junction. Bam, you have ground on pin 87.

ryeguy2006a

iTrader: (27)

Thanks hookem I appreciate the relay explanation. I'm curious if there would be any negatives to hooking it up in the way described above?

garys 68

iTrader: (1)

Why not use a trinary switch to trigger a fan. That's what they're designed for.

ryeguy2006a

iTrader: (27)

I would but the AC is already charged and I already have the relays and wire so it's going to cost me nothing but my time to do.

garys 68

iTrader: (1)

If you have aftermarket AC, like vintage Air, they recommend against that.

ls1nova71

iTrader: (4)

I agree with Gary, use a trinary switch. Wiring them the way you're thinking will have the fans running all the time, which will shorten their life and put an extra load on your electrical system. If you have a binary switch now to control the A/C, you can unscrew it and put a trinary switch in its place, they have Schrader valves under them so you wont loose any charge.

ryeguy2006a

iTrader: (27)

I'm running a 100% stock A/C system that came with my truck from the factory. I'm not opposed to the trinary switch, but I'm not sure if the settings will work correctly if I replace the stock switch. Here's another question, could I simply tap into the Binary signal from the stock switch and use that to trigger the relay rather than the A/C clutch?

garys 68

iTrader: (1)

No, the binary switch cuts out at low pressure to prevent compressor damage from coolant loss. It also cuts out at high pressure to prevent overpressurization. At the high pressure cutout is when you want the fan on. Just get the trinary, they're only about $30 and they've been working well that way for a few decades.
BTW, I've run dual fans. The Low temp off the ecu, the high off the trinary and the high ecu or a variable temp sensor. If you have both the high temp ecu and trinary, you could get a code for fan operation.

dixiebandit69

There's no need for a trinary switch if he is using PCM switched relays.

I'm using the three relay setup on my build with a blue/green PCM out of a Tahoe.

garys 68

iTrader: (1)

I just reread your post.... What components did you transfer over? The trucks run separate high and low pressure switches. However, I believe some systems require the BCM to get the ecu to control the AC system. Check your specific wiring diagram. It may be possible to run AC and fans off the ecu.
If not the trinary is the way to go, much simpler.
An explanation of your AC system would help.

ryeguy2006a

iTrader: (27)

Hi Gary,

Thank you for reading into my post further, I do appreciate it. My truck is a 2000 Silverado 2500 Classic that has the old body style of the 88-98 trucks. It came stock with a Vortec 5.7, and has had an LQ9 swapped in and using the stock wiring harness, re-pinned it to the same diagram as a 2002 Truck ECU. The guy that did the swap on my truck actually made a bracket that retains the stock Vortec A/C compressor in the alternator bracket on the LQ9, and there is an alternator relocation bracket on the passenger side. So the truck is using the complete untouched A/C hoses, compressor, and wiring as it came from the factory. With the exception of the wires that were re-pinned to match the 0411 ECU.

Many people do the 0411 ECU swap on the 96+ Vortec trucks as all of the pins are the same for the black box ECU and the 0411 because the 01-02 Express van used the same engine L31 Vortec 5.7, but with an 0411 ECU. The black box and the 0411 use the same terminals so it's a matter of just swapping the pins to match the right ECU. When I've reviewed the two wiring diagrams side by side, the A/C commands, requests and signals are all the same, so it must be a very similar setup as the 99-06 trucks used. Everything functions 100% on this truck currently, but with the efan swap I would really like the ECU to control the fans for A/C function if possible. I figured it would be a similar setup as the 4th Gen LS1 cars as far as wiring, but I can't seem to find any truck guys that have successfully gotten the 99-02 truck ECU to control the high/low fans and the A/C at the same time. It seems to be that you pick one or the other.

PS, sorry LQ4-E39 I sorta hi-jacked your thread.

garys 68

iTrader: (1)

Does it run a binary switch now?
Are the fans controlled by the ecu?

ryeguy2006a

iTrader: (27)

Hi Gary, I'm not well versed in the functionality of A/C systems, but I believe that there are both a high and low pressure sensors. From what I can find there are two separate switches, one is a cycling switch on the accumulator (part # 152962) that activates the low pressure and the other is a high pressure switch (part # 1550812) on one of the hoses. Not sure if they would both be considered binary switches?

garys 68

iTrader: (1)

Hmmmm, not sure how to address that. Not sure how the original fans and AC were controlled or how your ecu is programmed and integrated into the AC system.

ryeguy2006a

iTrader: (27)

My 2000 had a clutch fan that was attached to the water pump originally, so there never was a fan control in the ECU. From what I understand, there was a pin that would open up the A/C re-circulation door in the HVAC box to help regulate the pressure and temperature of the A/C system.

garys 68

iTrader: (1)

The 411 has a fan and the recirc door (also used as second fan). I'm just not sure how your ecu is integrated into the AC system with your combo.