LB7: Help requested - Tech 2 question on an A/C parameter

[dndj]

Hi all,

I recently purchased a Tech 2 (clone) and have had the opportunity to get familiar with it while debugging an A/C issue on my LB7.

The FSM states that the A/C pressure sensor should be readable as a ECM data parameter in "Engine Data 2". This is the 3 wire transducer on the high pressure side that reads 0-500psi with a variable voltage output from 0-5v, not the low pressure switch on the AC accumulator. I have been through every menu possible and can't find the "A/C Pressure Sensor" data readout.

My tech 2 is version 33.004, which I understand to be the latest. After I enter all the vehicle info, select the Powertrain -> F1 Data Display and I get "F0 Engine Data 1", "F1 Engine Data 2" and "F2 Fuel System". The tech 2 seems to be functioning fine, I can see tons of live data in the ECM, TCM and other modules but I cannot locate the "A/C Pressure Sensor" value.

Could someone with a tech 2 help me find where this is in the menus or confirm it's no longer there? Perhaps GM removed this parameter in some version of the tech 2 software?

Thanks!

 

[THEFERMANATOR]

Pretty sure the 3 wire pressure transducer is gas only, I've never seen a diesel that used one. Diesel's kept the low pressure switch on the accumulator, high pressure cutout switch, and the 350 on to 250 off recirc switch. It wouldn't be the 1st time GM printed incorrect ac 8nfo on the Duramax as I discovered doing my swap.

 

[dndj]

Pretty sure the 3 wire pressure transducer is gas only, I've never seen a diesel that used one. Diesel's kept the low pressure switch on the accumulator, high pressure cutout switch, and the 350 on to 250 off recirc switch. It wouldn't be the 1st time GM printed incorrect ac 8nfo on the Duramax as I discovered doing my swap.

Thanks for the reply. Low pressure switch is on the accumulator but LB7s do have a 3 wire pressure transducer up on top on the pressure line right as it leaves the compressor, FSM schematic shows it (red/black/gray wires). I am hoping someone with a Tech2 can point me to the right menu to read this or otherwise confirm it's not on the list of readable data any longer.

 

[DAVe3283]

The LB7 does have a pressure transducer, and it is readable over the data bus. I use EFILive to read it, so I don't know if the Tech2 can display it or not. If I get some free time today (don't count on it...) I'll try it with the Tech2 and let you know where I find it, if I find it.

You might try looking under the HVAC module, not the ECU. Wouldn't surprise me if GM stuck it under that, and actually reads both the HVAC module and ECU to get the data you want. I know it shows coolant temp under the HVAC module, so high side pressure might be there too.

 

[dndj]

The LB7 does have a pressure transducer, and it is readable over the data bus. I use EFILive to read it, so I don't know if the Tech2 can display it or not. If I get some free time today (don't count on it...) I'll try it with the Tech2 and let you know where I find it, if I find it.

You might try looking under the HVAC module, not the ECU. Wouldn't surprise me if GM stuck it under that, and actually reads both the HVAC module and ECU to get the data you want. I know it shows coolant temp under the HVAC module, so high side pressure might be there too.

Thanks, much appreciated. I did check the HVAC screens in the Tech2 as well and didn't see that data available there either, but all the stuff in the 3rd picture I attached above is there (recirc/outside, hot/cold door positions, etc). When you get a chance, if you could verify one way or the other on your Tech2 I would be grateful. :thumb:

 

[DAVe3283]

When you get a chance, if you could verify one way or the other on your Tech2 I would be grateful. :thumb:

Huh, I thought I remembered it being available on the Tech2, but it is not. I'm running NAO 33.004, and no A/C high side pressure anywhere. It does work through EFILive, so that's probably how you'll have to go if you need the raw number. The Tech2 only displays A/C clutch command On/Off state.

 

[dndj]

Huh, I thought I remembered it being available on the Tech2, but it is not. I'm running NAO 33.004, and no A/C high side pressure anywhere. It does work through EFILive, so that's probably how you'll have to go if you need the raw number. The Tech2 only displays A/C clutch command On/Off state.

Ok, thanks for checking. I have the same version 33.004 that you do. I am guessing GM may have removed that parameter in favor of something else somewhere along the way, especially if the Tech2 has a limit on the total number of parameters that can be monitored. I will use EFIlive to monitor the A/C high side pressure instead.

Thanks again for the help.