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Duraburb HVAC control

Kennedy.engine

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Hello, I’ve stumble across this forum quite a bit looking for info while doing my duramax swap but this is my first post.

I’m in the process and have been for awhile of doing an LLY/Allison swap into a 1999 gmt400 k1500 gmc suburban.

I’ve run into quite a few issues but I am looking for some info about getting the AC to function.

Everything in the ac system is from the suburban, including the compressor which mounted perfectly onto the duramax.

Using alldata it looks like the ac control for the suburban goes through the VCM of the gas engine (which I have removed).

The duramax engine harness and ecm also have ac controls.

I’m wondering if I will need to install the VCM back in place just to get the ac to function? Or can I bypass the whole suburban control system and make a stand alone system using the duramax ecm and wiring?

I apologize for such a long post and I’d like to thank anyone in advance for helping out.
 
I believe on that setup your going to have to bypass the ECM entirely and wire it to run on it's own system. You can make it work, but you're going to have to change your wiring over to that of the LLY. It's doable, but it will take some work to swap things over and make it all work.
 
Okay that’s what I was thinking. It looks like the LLY ecm controls the ac clutch relay, then the power from 87 on the relay goes through the clutch, low pressure switch and then goes to the HVAC control module which communicates the info via class 2 serial data to the ecm.

So my question is will I have to retain that HVAC control module from the LLY or can I bypass it somehow to get the ecm to engage the ac relay?

And thanks for the help fermanator, your build thread was awesome I don’t know if it’s my browser or something but the pictures don’t show up. Either way the information in the thread is great thanks for sharing it 👍 it’s helped me a ton with my build haha
 
From what I understand on the 03+, you have a low pressure switch that controls a ground signal to the ECM to control the cycling 9f the compressor clutch. The AC control head can send either a class 2 j1850 data bus signal or there is a pin you can supply power to to enable the AC system. And 03+ uses a pressure sensor mounted in the high side AC line to the ECM to monitor the high side pressure(01/02 did not use this pressure sensor). Your Suburban uses a high pressure switch to turn on recirc mode threaded onto the high side line, a high pressure safety switch 8n the compressor, a low pressure cycling switch at the accumulator, and the control head sends a power signal to the PCM to turn it all on(via the high pressure safety switch). You can put the high pressure sensor where the recirc switch is now, omit the high pressure safety switch, and rewire the low pressure cycling switch. If you want to keep the high pressure recirc switch, you'll have to install a 95 condenser, and mount the switch there.
 
Awesome thanks for all the info. So Ill need to find the PIN number in the ecm that will activate my ac and install a switch for it, I’ve noticed alldata isn’t very detailed in the descriptions for the ecm pin outs.
 
Alldata and the factor manuals give quite a bit of false information for doing swaps I've found. It was annoying getting everything put together and then having to go back, find why it wasn't working, and then find the correct info that was wrong in alldata.
 
Yeah I’m a little concerned about all the electronics working correctly. I’m finishing up my wiring soon so once I get batteries I’ll be able to test it out.

I made my own fuse/relay panel and used all data to figure out what wires needed to be powered for the suburban body harness, then figure out what wires in the duramax needed to be powered.

I’m finishing up the throttle pedal and instrument panel harnesses which are both from the duramax truck then I’ll be ready for power. If nothing catches on fire when I turn the power on I think that’ll be a great start haha.
 
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