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LTX and LSXPutting LT1s, LS1s, and their variants into Third Gens is becoming more popular. This board is for those who are doing and have done the swaps so they can discuss all of their technical aspects including repairs, swap info, and performance upgrades.
I need help wiring up the AC in a swap I’m doing. Car has an ls3/t56 with a stand-alone psi harness. I trimmed the factory harness down to starter and power wiring so none of the ac stuff is there. Does anyone have a diagram they can post? I’ve searched for days and cannot find anything on it. Thanks in advance.
Pic of the car. It needs a bath badly. But has the Sanden Compressor and other than that it’s all factory parts.
AC wiring is mostly separate from the rest of the car. Comes through the firewall near the heater hoses. Has at least one vac line in it in addition to the wires, probably 2.
If you cut it or something, you'll need to get another from somewhere.
If using a factory ecm you have to add a pressure switch from 4th gen on the high pressure side, it has 3 wires, then you wouldn't use the 3rd gen low pressure switch anymore so you could cap that off. The factory computer needs the input from the car, an output to trigger the clutch relay(as long as pressures are within a specified range), and also a signal wire from ac clutch positive just so the computer knows that the relay and fuse are working and ac is actually on. I found my diagram on ls1tech.com.
Half the AC wiring is in the engine harness, so you'll need to pull that out or replicated it, or fab up new AC provisions. I am not sure what the factory strategy for the AC wiring on the gen IV engines
I can't believe people keep buying those cheap POS PSI harnesses
Half the AC wiring is in the engine harness, so you'll need to pull that out or replicated it, or fab up new AC provisions. I am not sure what the factory strategy for the AC wiring on the gen IV engines
I can't believe people keep buying those cheap POS PSI harnesses
I’ve used PSI harnesses on multiple builds with 0 problems. I’ve also modified my own to be plug and play. I’d rather buy a harness than to spend days rerouting and lengthening a harness that could have problems.
E38 is tricky from a PCM perspective - as you noted the PCM will be expecting a message on the CANBUS for request. You could tune around this in the old DBW PCMs but not the E38+ (as far as I know).
I am planning on using the RPM Extreme AC module which takes the 12v signal from the HVAC controls then simulates a message on the CANBUS to command AC. The PCM still gets wired with the high pressure switch and needs to be safe to actually turn on the AC, then the PCM would send the 12v signal to the AC relay.
I never found a way to have the E38 control the A/C clutch. I used a Speartech harness, and this was their advice:
" However, we don't have any way to control A/C during a swap. That is the benefit of using vintage air. Vintage air is a standalone system and doesn't require any signal from the ECM. The V8 engine doesn't need an idle bump when compressor comes on and everything will work just fine for you. Our harnesses that contain A/C is simply a convenience wire to get a wire from the A/C clutch to inside the vehicle without the need of running a wire outside of our harness."
The Vintage Air website said:
"The SD 508 Compressor is recommended for any Vintage Air System. It pumps 8.4 cubic inches per revolution with a maximum 6000 sustained RPM range."
So that’s how I run my A/C. The high pressure switch was on the stock A/C compressor. To add a high pressure switch to my LS swap, I bought a Vintage Air trinary switch and -4an port.
So just to update for others searching for the info, The Light Green Wire from the HVAC Harness needs to go to the Low Pressure Switch, then out of that switch is the light blue wire that goes into the high pressure switch. From that switch it goes into the A/C Compressor. I am not using the PCM to command or Bump the idle, it seems to idle and run fine without it. The fans are on a Derale Dual fan Relay that has an AC wire that taps into the 12v A/C Command wire. That tells the fans to kick on.
I searched and searched and couldn't find the info easily that wasn't confusing so there it is.
With an LS3 and stand alone PSI harness, you will likely need to wire the Sanden compressor clutch through a relay triggered by the ECU or a pressure switch. Make sure you also account for high and low pressure safety switches. Teams at Luxury Rides LLC often suggest confirming pinouts with the harness manufacturer before final connections.
