Vintage AC and kicking on fans

[6600DURAMAX]

Have a K5 blazer with a complete Vintage Air A/C kit installed.

Blazer has a LS3 with dual electric fans – fans run through the emc/pcm and are set to come on at 165 then kick off tcm speed has reached 30mph. My question is how do I wire my fans to kick on and stay on when the AC switch is activated?

There is no way in the pcm/ecm programming to do this.

Concern is overheating/ pressurizing the high side of the compressor when there is no airflow ( for instance upon startup or sitting in traffic ) before the fans activate

[6600DURAMAX]

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[Sheepdip]

Relay from your A/C "On" switch to your fans.

[6600DURAMAX]

Originally Posted by Sheepdip

Relay from your A/C "On" switch to your fans.

Even though I wired the entire vehicle I would say I'm amateur at best when it comes to wiring.

I have both fans on separate relays now and they tie into the PCM wiring

Could I splice into the same relays with the A/C on switch?

In my mind that would send signal to the relay just as the PCM would. just want to ensure it doest screw with the PCM

[Sheepdip]

Without knowing your current wiring diagram that's a 50/50 shot. The trigger for your fans should (and that's the key word here) be a grounding wire.

[LNP]

Did you check with Vintage Air to see if they can tell how to wire it up? For the PCM to activate the fans it would have to have a signal from the AC controls to the PCM so it knows you turned the AC on. If the PCM is out of a donor car look up the wiring diagram fpor that car and follow the wires for the AC to the PCM. As said before computer control cars use the ground as the signal not the positive.

[6600DURAMAX]

Vintage Air recommends a Trinary switch vi the binary switch I currently have in place. This switch will sense when the pressure is above 250 psi in the condenser and turn on the fans.

Just ordered one !! Will let you know how it works

[LNP]

Good to know hope it works for ya.

[A1971Blazer]

just addressed this on the LS1 swap in my '67 C10
you can't just wire the trinary to one of the PCM fan trigger grounds,
it will work but will set a P0480 or P0481 code depending on which fan it's connected to.

check this post for the solution.
I rewired mine this way and it works now without setting a code.
https://67-72chevytrucks.com/vboard/...d.php?t=853200

[RustyPile]

Originally Posted by 6600DURAMAX

Vintage Air recommends a Trinary switch vi the binary switch I currently have in place. This switch will sense when the pressure is above 250 psi in the condenser and turn on the fans.

Just ordered one !! Will let you know how it works

I have 2 fans on the radiator. That's exactly how I have one of mine wired, and it works perfectly... The other fan is on a relay activated when the ignition is switched ON. A sensor in the radiator provides the ground path, and set to turn off if coolant in the radiator is below 165*...

[Accelo]

The bad news it you will have to drain and fill the system to install the Trinary switch.

There is no way in the pcm/ecm programming to do this.
I am surprised this isn't possible, my early LS1 computer has an "air is on grounding terminal" Every PCM system I have seen has an output for the scanner to read the status of the "AIR". I would look closer at the factory system for the grounding when AIR is active and the matching computer input from the AIR. I could be full of it, as I though the ECM for the LS3 used PWM for fan speeds. Some more research may be necessary.

[Richard]

I pinned my PSI harness for the factory A/C pressure sensor. Am running the e67 ecu that came with the engine. I am also using a variable speed 850w PWM fan controlled by ecu. My research revealed that the ecu will automatically bring my fan up to 50% duty cycle when A/C pressure rises above the high threshold. Of course the ecu will adjust fan speed according to engine temp as well.