Several days ago I posted about reading the status "A/C Permission" on my two GM vehicles with CJ2 automatic controls. At the time I thought I was expanding on what I had previously posted about various A/C data parameters. Looking back through the thread now it appears I have not previously posted much of anything for A/C parameters beyond the high pressure. Fell through the cracks I guess.
Perhaps I was unsure about what I had. I have recently done more research and am more confident of what I am seeing.
The first one here frequently appears first before the A/C relay is commanded on. The technical details of what it is I do not know, I just see its' behaviour.
Name:~A/C Request (Pid 1100 Bit 1)
ShortName:A/C Request
ModeAndPID:0x22110001
Equation:Lookup(bit(A:1)::1='ON':0='OFF')
Min Value:0
Max Value:1
Unit:
Header:6C10F1
Scale:x1
These next two seem to be the same thing just appearing in two different PIDs, one in the range where transmission PIDs are generally seen. They both indicate that the PCM has activated the A/C relay which should send power to the compressor clutch. These both go high even if the relay is removed so it clearly is not proof that power has actually been sent to the clutch, just an indication that the PCM believes it has grounded the control circuit of the A/C relay.
Name:~A/C Relay Command (PID 1110 Bit 2)
ShortName:A/C Relay
ModeAndPID:0x22111001
Equation:Lookup(Bit(A:2)::0='OFF':1='ON')
Min Value:0
Max Value:1
Unit:
Header:6C10F1
Scale:x1
Name:~A/C Clutch Request (PID 1954 Bit 4)
ShortName:A/C Clutch
ModeAndPID:0x22195401
Equation:Lookup(Bit(A:4)::0='OFF':1='ON')
Min Value:0
Max Value:1
Unit:
Header:6C10F1
Scale:x1
The foregoing PIDs are mode 22 requests, the type normally used for acquiring data. The next ones use a mode 23 direct memory read to get data otherwise unavailable at least without onerous methods. As such I again must say I can only state that these work on my 2002 with factory calibrations. Eventually I will grab HVAC modules of varying years from the Upull for the purpose of nailing down these data points.
This one is the status line coming back to the PCM from the clutch. I believe it carries the 12 volts that is sent to the clutch back to the PCM as a feedback signal confirming the relay has indeed closed. In the wiring diagrams it looks to be connected after the compressor thermal protection switch as well so if that opens this signal should drop out.
Name:~A/C Clutch Feedback Signal
ShortName:A/C FDBK
ModeAndPID:0x230020F801
Equation:Lookup(bit(A:3)::0='Off':1='On')
Min Value:0
Max Value:1
Unit:
Header:6C98F1
Scale:x1
This should need no explanation, it is the status of the lo pressure switch.
Name:~A/C Low Pressure Switch
ShortName:A/C Lo Pres
ModeAndPID:0x230020F801
Equation:Lookup(bit(A:4)::0='Closed':1='Open')
Min Value:0
Max Value:1
Unit:
Header:6C98F1
Scale:x1
This too is self explanatory. This address works for my 2002 CJ2 but the address is slightly different for my 2005 Yukon. One other thing worth a mention. This is the first time I have come across a data parameter that reports in degrees Fahrenheit instead of Celsius. The TrailBlazer gives me Fahrenheit but the Yukon gives me Celcius. The Yukon address btw is 0x2475 instead of 0x24BA.
Name:~Cabin Inside Air Temp °F (2002 CJ2)
ShortName:Cabin Air °F
ModeAndPID:0x230024BA01
Equation:A-40
Min Value:-40
Max Value:215
Unit:°F
Header:6C98F1
Scale:x1
All of this is contained in my spreadsheet seen here...
docs.google.com