No A/C, driving me crazy.

[TJ Baker]

Get a scanner that will read all the AC PID. My 50 dollar top scan dongle will read all of this.View attachment 490272View attachment 490273

I have an Autel MaxiAP200 that does much the same. Bought them years ago for $35, they are now like $60.

Also of course the Tech 2 knockoff.

And then, being the inquisitive sort I read out the HVAC memory of my two GM vehicles and studied the contents. Both are CJ2 automatic systems. I located the memory addresses for some useful bits so I can now read some of that data using service $23 in apps like Torque Pro, Car Scanner ELM OBD, OBD Fusion and so on.

 

[TJ Baker]

It might be under another tab. This is the HVAC tab. Actual pressure feedback is probably under the general tab if its there.

It will show me rear air ride system pressure so I would assume it would show actual ac system pressure too.

A/C high pressure will be shown in the engine section. This is because the high pressure sensor is wired to the PCM, not the HVAC module.

Anyone with Torque Pro or similar can read the high side pressure if they set up the custom PID for it. It's not hard to do. I can advise if anyone wants to do that.

 

[nonickatall]

Why so complicated? Just measure, if your low pressure sensor has 0 Ohm.
This is the basic requirement for everything, because it indicates that the system has enough refrigerant.

99% of ac systems stop working, because of a lack of refrigerant...

 

[mikez71]

Figuring he already tried jumping the low pressure switch, and he couldn't display the AC pressure sensor..
Since he could add the widget to his display, and assuming it would know the correct PID..

Maybe an issue with his pressure sender wiring to ECM?
Although he said the shop verified all inputs...(Maybe they only verified the inputs under the HVAC tab?)

 

[TJ Baker]

Why so complicated? Just measure,

I am measuring. I am seeing what the controllers see. Even if you measure at a sensor that is no guarantee you are seeing what the controller sees, and what the controller sees is what matters most.

Additionally I am doing this right from the comfort of the drivers seat. No looking for tools, no opening the hood, no concerns if it is raining out. I can do it at any time and can record the data so I can catch Intermittent issues that will nearly never be seen with a meter measuring for a few moments at best.

 

[nonickatall]

I am measuring. I am seeing what the controllers see. Even if you measure at a sensor that is no guarantee you are seeing what the controller sees, and what the controller sees is what matters most.

Additionally I am doing this right from the comfort of the drivers seat. No looking for tools, no opening the hood, no concerns if it is raining out. I can do it at any time and can record the data so I can catch Intermittent issues that will nearly never be seen with a meter measuring for a few moments at best.

You're absolutely right, a good software and reading the system is better than everything, but if you don't have the possibilities, then just measure the few values which are relevant in this case.

That can give a good direction where the problem comes from.

For example: As I said, most problems with ac systems is a lack of refrigerant.

So measure your low pressure switch if it's open, there is enough refrigerant.

So your clutch should engage. So measure if you have 12 Volt at the clutch and measure the ohm of the coil, and you have 99% of ac failures detected.

 

[LsHart]

Didn't u say u replaced the ac system?

 

[LsHart]

Command ac on and back probe compressor pigtail and look for ground and power.

 

[TJ Baker]

I had to run a short errand this morning. Decided to grab some data. Seen here is recorded data using Car Scanner ELM OBD app and a Veepeak Bluetooth OBDII adapter. Depending on specific Veepeak model they run from $15 to maybe $30. Some of the PIDs are custom, I created them for the 2005 Yukon 5.3.

 

[clandr1]

my truck has been at the local Chevy dealer since Monday. They called today and said their diagnosis is a bad PCM. It’ll take them about a week to get a replacement unit. I’m moving forward with the repair and crossing my fingers.

Thank you to all who posted with helpful suggestions and feedback.