Adding AC after ls swap

91burb2500 said:

After 3 failed R4 type compressors, I went with the Sanden 508 and top mount bracket kit from Holley. It wasn’t cheap but it was the easiest option. With the help of this great board, figured out that my condenser was the weak link and upgraded to a parallel flow and it was money. It was suggested to run the bigger 7 series Sanden, but with the new condenser the 508 is working great to run front and rear air on the Suburban. All the other components on mine are factory, but running 134a. Those R4s suck a bunch of power too, noticeable on the butt dyno for sure.

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good info, saved to my spreadsheet for A/C

Good information... I have a 1987 GMC Suburban that we installed a new LS3 6.2L and we used a GM Performance Wire Harness, our problem now is the relay is built in for the cooling fan's and trying to find a wire diagram on how to make the factory A/C work? I have the green wire from the low-pressure switch on the accumulator, and from the accumulator it runs to the dash that turns on the A/C on/off, I have 12v on the line when I turn the AC on. I have flushed the system and replaced the accumulator, Pump, condenser. I hope this is enough information but if you have questions let me know.

Thanks

Curt

I have my dual fans wired via relays controlled by the green wire, when the compressor kicks on they turn on. My fans are Fluid Dynamics extreme fans, so I have one relay per fan due to the high amp draw (they pull a ton of air), but they are in parallel so they both kick on at the same time. The way I'm set up running an aftermarket stand alone harness, the PCM also has fan 1 and fan 2 programmed to turn on with temp, this way I always have air flow for the A/C when in use and if not, temp will still turn on the fans to keep things cool.

My fan 1 control turns on at 195 degrees and off at 190, both fans again are wired to a pair of relays in parallel so both turn on at that temp. My fan 2 lead is controlling the factory pusher fan on the front of the radiator as an "emergency backup" that turns on at 210 and off at 205. The pusher is on its own relay separate from the primary fans. With this set up even sitting in stop and go traffic, I have not had the pusher turn on. Those big fans suck a ton of air and with the big block radiator, I have never gotten over about 203-205 according to my OBD2 Bluetooth dongle.

iamtherealJayy said:

After a very long time, and replacing the LS the blazer finally runs. So I’m back to ac, can I use a full system from a 88-91 k5, burb etc? And a bracket to move compressor to the top and have a factory system? After reading alot about vintage air it just doesn’t seem like the cost is worth the reward.

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I see this is a week or so old but here's the bracket that I went with to retain a factory LS truck compressor relocated to the top: It's from ICT Billet. Just note: You don't have to run the idler pulley that's in the pic at the top. You do have to buy a different pulley for the compressor, they have that also.

The Holley kit is basically the same, I just did not have the OEM compressor so I got the complete kit with the comp. One thing to note on the kit I got was I had to shim the whole bracket out one M12 grade 8 washer to align the belt and keep it from squeaking.

91burb2500 said:

so I have one relay per fan due to the high amp draw

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post # 30. This will decrease any current draw spikes (if you have any) for cheap and easy.

Current spike elimination

https://www.ametherm.com/inrush-current/inrush-current-faq.html

These are 14” fans and run 16-20 amps each continuous per the builder after startup. I melted the fuse box with the 4-pin GM style relays originally, so now I’m running dedicated 40 amp circuits with 10 gauge wire being fed with a 6 gauge cable from a bus bar off the battery. Got all the juice they can handle now, but I wish I would’ve known about those.

That would’ve for sure solved the startup spikes that was popping a 30 amp fuse and probably saved the original relays in the stand alone LS harness.

I did a 6.0 swap using OE harness and Tejas motor mounts to mount the Saden AC compressor low. I replaced the accumulator, evaporator, expansion valve, and all lines and hoses using factory HVAC controls. It is charged and cooling good, the issue I have is the LS ECM doesn't know the AC compressor is running to adjust the DBW throttle body IAC so at idle the engine RPMs are really low. My question is how do I communicate to the ECM that the AC is on?