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#1 |
Registered User
Join Date: Nov 2000
Location: Wheatfield IN, USA
Posts: 1,113
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Vintage AC and kicking on fans
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
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1972 K5 Build - plans - LS3-6L80e-One Tons..... 1971 CREWMAX Build.....at body shop for couple more years ![]() |
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#2 |
Registered User
Join Date: Nov 2000
Location: Wheatfield IN, USA
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Re: Vintage AC and kicking on fans
pic
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1972 K5 Build - plans - LS3-6L80e-One Tons..... 1971 CREWMAX Build.....at body shop for couple more years ![]() |
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#3 |
Senior Member
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Location: Waterford California
Posts: 2,525
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Re: Vintage AC and kicking on fans
Relay from your A/C "On" switch to your fans.
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#4 |
Registered User
Join Date: Nov 2000
Location: Wheatfield IN, USA
Posts: 1,113
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Re: Vintage AC and kicking on 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
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1972 K5 Build - plans - LS3-6L80e-One Tons..... 1971 CREWMAX Build.....at body shop for couple more years ![]() |
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#5 |
Senior Member
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Location: Waterford California
Posts: 2,525
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Re: Vintage AC and kicking on fans
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.
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#6 |
Registered User
Join Date: Mar 2014
Location: Pekin, Illinois
Posts: 413
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Re: Vintage AC and kicking on fans
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.
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Harley 1969 Chevy C-10 Long Bed, 350cid, 700R4 |
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#7 |
Registered User
Join Date: Nov 2000
Location: Wheatfield IN, USA
Posts: 1,113
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Re: Vintage AC and kicking on fans
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
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1972 K5 Build - plans - LS3-6L80e-One Tons..... 1971 CREWMAX Build.....at body shop for couple more years ![]() |
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#8 |
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Join Date: Mar 2014
Location: Pekin, Illinois
Posts: 413
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Re: Vintage AC and kicking on fans
Good to know hope it works for ya.
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Harley 1969 Chevy C-10 Long Bed, 350cid, 700R4 |
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#9 |
Senior Member
![]() Join Date: Nov 2013
Location: East Tennessee
Posts: 2,145
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Re: Vintage AC and kicking on fans
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
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1967 C10 Step side 1968 C10 Step side 1970 Chevrolet K/5 Blazer 1972 Chevrolet K/5 Blazer ............. ![]() |
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#10 |
Registered User
Join Date: Dec 2017
Location: Elkhart, Texas
Posts: 1,699
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Re: Vintage AC and kicking on fans
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*...
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#11 |
Senior Member
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Location: washington
Posts: 2,238
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Re: Vintage AC and kicking on fans
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. |
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#12 |
Senior Member
![]() Join Date: Dec 1999
Location: Southern California
Posts: 2,805
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Re: Vintage AC and kicking on fans
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.
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Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 |
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#13 |
Registered User
Join Date: Nov 2000
Location: Wheatfield IN, USA
Posts: 1,113
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Re: Vintage AC and kicking on fans
My tuner says that this ECM doesnt have a AC pin it was controlled by the BCM
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1972 K5 Build - plans - LS3-6L80e-One Tons..... 1971 CREWMAX Build.....at body shop for couple more years ![]() |
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#14 |
Registered User
Join Date: Oct 2016
Location: Dallas Texas
Posts: 3,087
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Re: Vintage AC and kicking on fans
.
My MSD Atomic EFI computer controls the fans based on temp settings. To get the A/C to trigger one of my fans, I ran a tap wire from the binary switch to the relay 12v trigger for the fan I wanted to kick on with A/C. Essentially I'm tapping into the compressor clutch 12v. Later, I did the same thing with a pusher fan placed on the condenser. Since then I have installed a trinary switch for the purpose of having the supplemental pusher fan only kick when pressure limit is reached. Reminds me...I need to finish that up! Hth, -Kevin
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67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold |
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#15 | |
Senior Member
![]() Join Date: Dec 1999
Location: Southern California
Posts: 2,805
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Re: Vintage AC and kicking on fans
Quote:
Edit- Popped into my head. Maybe look at the pressure sensor signal to ecu as "A/C is on so turn on fan" I am using this to integrate the pressure sensor and high/low pressure switch. https://bp-automotive.com/product/ls...re-transducer/ The pigtails for the switches are available but not sold by BP. What ECU are you using? The great benefit of using this option over the A/C compressor lead is that the fan will only run when needed. Using the compressor lead or cycling switch will make fans run always when A/C is on. Fan is not needed at highway speed. Eliminates trinary switch and extra wiring.
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Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 Last edited by Richard; 07-20-2024 at 02:42 AM. |
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