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Umm, no it's not. How do you figure?

 

Instead of a switch use a 2nd relay. Where you have your switch drawn, instead connect those two wire to the Common and NC contacts on the relay. Then control the 2nd relay's coil off your O/D solenoid wire. Now whenever your O/D kicks in the coil energizes and the power to the fan will drop out automatically.

 

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Granted he drew the relay incorrect. He has the battery to fan wiring going through the coil and the dash switch going to the contacts. But I gave him the benefit of the doubt that he knew what he meant to draw.

 

HI all...

I did it yesterday. I took my time and it seems to be a success although I haven't tested it with a temp gauge.

I do notice a drop in AC temp when I turn it on. I also notice a large difference on how quickly it gets colder. I wired it like in my picture, and did hook up the relay correctly.

As for the condenser, below are all the bolts and associated parts I had to take out (other than the grille) to be able to get my had behind it to mount the fan. (see arrows)

I believe this project was a success. Unfortunately, I have to get the top repainted and the van is in the paint booth now. When I get it back, I can use a gauge and get some solid numbers. But by feel, I would say it almost is a 10 degree drop.

Parts that had to be taken off -->



There is a plug left of the booster which is a real nice place to run the switch wires in..



Here is a pic of where I have the relay



Took me about 4 hrs to do...but I was talking my time, dealing with my kids and generally dickin around doing it

 

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I know this maybe a little late, but I also have a fullsize van although its a 1997 Chevy Express that had an inferior a/c system at idle. It would blow about 50*F at idle, but cool into the low 30s driving down the highway at 50+ mph. I ditched the R134a and switched to R152a. With R152a alone it would idle in the low 40s. For power and MPG gains and removed the clutch fan for a pair of factory GM puller electric fans. Using a larger 34" wide 454 radiator. With the 2008 Tahoe fans wired in the factory 3 relay Series/Parallel 2 speed arrangement even on low speed at idle the a/c stays at 35*F on a 105*F day and discharge pressure stays under 200 PSI at idle. I also have a larger external transmission cooler with its own fan in front of the condenser that activates on a transmission temperature controlled thermostatic switch and have yet to hear the fan kick in on it. What I have found is a pair of puller fans with a shroud is much more efficient than the a clutch fan.

I think your electric fan setup could be greatly improved using a pair of puller fans with a proper shroud to fully cover the radiator.

 

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Not a problem just something to consider. Amperage draw is nearly a non issue with the GM setup. When the fans are wire in series to run on low speed, the resistance increases 4 fold over having both fans wired in parallel. So my low speed fan operation draws 10 amps and high speed 40 amps and that is running BOTH fans moving lots of air.. Low speed is adequate to cool the engine 95% of the time and keeps the head pressure lower than the mechanical fan ever did. You almost never even hear the dual fans wired in parallel either as they run on 6 volts at roughly 1/2 speed. You can see how effectively they cool my 350 within seconds of turning on. Having run a large power hungy single fan aka Taurus fan I can say the dual setup works much better.


Have you considered an od shutoff relay to disable the main fan when the pcm commands overdrive? On my GM I am lucky enough to have partial pcm control over the setup.