The best electric fan install with a trinary switch

[kylenautique]

Hey so I wanted to make this writeup because there are a lot of "how to" electric fan installs for these trucks, but I wanted to show how to control the fans and air conditioning the best way. Almost all GMT400 trucks can use the ECM to control the fans. The later model TBI computer can control it, and the stock vortec (I can't verify 1996-1997) ECM can also control it with some programming and adding one wire to the ECM harness. You can also use a simple temp switch. I installed fans on my 1998 K1500 and used a dual fan from a 2006-2007 Tahoe/Suburban/Silverado Classic. The fan fits perfectly with very little modification and looks 100% OEM. The biggest issue is how to control the A/C compressor and the electric fans. The most common way is to run a third relay which kicks the fans on every time the compressor turns on. Here's the problem with that setup... Its a huge surge on the electrical system. Sure, you can upgrade to the 1999 and up LS alternator (which I did), but that will not cure the problem. The problem is when driving at night, every time the compressor and fans kick on, your lights will dim for a millisecond. Its very annoying. My headlights are rigged up with relays too, and they still did it. The solution is a trinary switch. Why is the Trinary switch the best solution for the A/C? It relies on pressure to kick the fans on. The compressor will turn on and run for a little bit before the pressure builds up enough on the high side, and the trinary switch will trigger the fans to turn on. Even better, when you are driving down the freeway, your fans will never turn on when your A/C is running. More get up and go power, and maybe better fuel economy. The only problem is that there is no where to add one into the stock system. Well, here is how you do it!

You need to buy a few things..
-Electric fans from a 2006-2007 Tahoe/Suburban/Silverado Classic. I got mine from a junk yard for $60
-Vintage Air threaded adapter https://www.amazon.com/gp/product/B002VW3MFU/ref=ppx_yo_dt_b_asin_title_o09_s01?ie=UTF8&psc=1
-Trinary switch https://www.amazon.com/gp/product/B003R4156E/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1
-R-134 service port socket https://www.amazon.com/gp/product/B002YKK234/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
-R-12 to R-134 service port adapter https://www.amazon.com/gp/product/B07R76KH59/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
-8mm x 10mm 1.00 pitch thread die
-GM R-134 high pressure service port (any auto parts store)

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Step 1.
Install the electric fans. You will need to come up with a top hold down bracket. I cut my radiator hold down brackets and welded some steel on them to bolt the fans to the core support. Same process on the bottom. The fans come with two tabs on the sides for the later model radiator. Cut them off. It makes installing and removing the fans a ton easier! I had to slightly bend my power steering hose too. I wired my fans with a custom relay harness made by my local tuner. 10 gauge wire leads for both fans with 30amp **** fuses going straight to the battery. I also used Hella Relays. There are plenty of fan harnesses out there, so pick a quality one or make it your self.

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Step 2.
Take the vintage air threaded adapter and change the male thread end size with the 8mm x 10mm 1.00 pitch thread die. This will allow you to screw this fitting into the R-134 service port internal threads. Take your new R-134 service port and remove the Schrader valve or check valve. Screw the vintage air fitting into the top of the R-134 service port and attach the trinary switch. I recommend using lots of thread tape or thread sealer on the vintage air fitting going into the R-134 service port to avoid leaks.

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Step 3.
Remove the stock R-134 high pressure service port with the special socket. If you can do it fast enough and install it before all the Freon depletes, you can simply add more R-134 back to the system. If you deplete it completely, you will need to properly re-charge your A/C System. Connect one blue wire to ground, and the other blue wire on the trinary switch to your ECM or temp switch controlling the fans. You don't use the two black wires for this application.

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You are good to go! You have successfully modified your R-134 port back to a R-12 port. If you need to re-charge your a/c, remove the trinary switch, connect the two ground wires together to make the fans turn on, and use a R-12 to R-134 adapter to recharge the system. This is on the high pressure side, so if you are just adding R-134 to the system without gauges or anything that requires the high pressure port, just leave the trinary switch connected.

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For ECM fan control, I have mine programmed to come on at 202F and off at 197F. My fans also turn off at 50mph. I hope this helps everyone installing electric fans! Your truck will feel more powerful without the clutch fan.

 

[kylenautique]

These are my brackets I made to hold down the fans..

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[1997]

nice job and post.
my Fan's only locked in once in my travels so far and it was definitely noticeable, haha.

 

[MrPink]

Unfortunately this only works for those of us that have A/C, I did mine a bit different and it is an independently wired setup.

 

[eran tomer]

how do you connect the ecm to control the fans?
and did you upgrade the alternator?

 

[kennythewelder]

Here is a link to my write up on mine.
Thread 'Electric fan swap, on the cheap' https://www.gmt400.com/threads/electric-fan-swap-on-the-cheap.41756/

 

[MrPink]

how do you connect the ecm to control the fans?
and did you upgrade the alternator?

I did neither, my fan is on an independently wired setup with a coolant temp sensor on at 185* off at 210*

 

[Schurkey]

my fan is on an independently wired setup with a coolant temp sensor on at 185* off at 210*

Huh?

Your fan turns on at 185, and off at 210???

Isn't that backwards? I'd expect it to turn off at a lower temperature than it turns on at.

 

[kylenautique]

how do you connect the ecm to control the fans?
and did you upgrade the alternator?

Yes I upgraded to a GMT800 alternator. You will need a tuner to set your ECM fan control settings. Just google where the wire needs to be pinned in to the ECM. I can take a look to see where it went on my truck if you need. Just DM me.

 

[1998_K1500_Sub]

Step 3.
Remove the stock R-134 high pressure service port with the special socket. If you can do it fast enough and install it before all the Freon depletes, you can simply add more R-134 back to the system. If you deplete it completely, you will need to properly re-charge your A/C System.

While I really like what you're trying to do in this fan retrofit, this step sounds troublesome.

It's known that PAG and liquid R134a are miscible.

Allowing the system to blow-down after removing the service port, even for a brief while, is going to carry some oil out of the system... more, if liquid R134 finds its way to the opening, because of the oil miscibility. Replenishing that oil is a guessing game since there's no reliable way (IMHO) to determine how much may have been blown out.

Too, any R134 exiting the port during this "fitting remove / replace" operation could be a frostbite concern if one's hands / eyes / face aren't protected, particularly if liquid R134 were present.

I don't want to be a Chicken Little but... I don't think this is a good idea.

If I had to do the same thing, I would probably take the truck to an AC shop, have them evacuate the system and then backfill with shot of R134a to bring the system pressure to 0 PSI or maybe a few PSI above zero, then swap the fittings under zero or very low pressure, and *then* recharge the system. It's more money but it eliminates the concerns I noted earlier.