: A/C help needed

06-10-06, 12:29 PM
I was just driving to my house on the typically deathly hot Houston day when my nav screen displays "service A/C system" and continues to turn my A/C off. This comes as a surprise to me as the system was working fine and has not given me any trouble.

Having gauges and R134 in my garage I was wanting to check the pressures and add any refrigerant if needed...but the A/C will not come on at all.

Does anyone know how I can reset the A/C system so I can check the pressures?

If we find out, this may be another good addition to the FAQ....I was almost as surprised to not find it with everything else known to man being there. :eek:

Thanks for any info

06-11-06, 02:30 AM
Wow, This took some digging... Good thing I am still up due to jet lag (and as usual have nothing else to do)

From the service manual:

If the ECM detects a failure in the A/C refrigerant pressure sensor or circuit, the class 2 message sent to the HVAC control module will be invalid. The HVAC control module will then send a request to the radio for display of the SERVICE A/C SYSTEM that will be displayed on the DIC. The HVAC control module will also display A/C OFF on the module as long as the condition is present.

Sounds like if the issue wont go away, either you have a leak, or the sensor is bad.


06-11-06, 07:54 AM
Check the harness going to the sensor and make sure the connector is seated all the way. The sensor is on the driver's side hard aluminum A/C line and points down towards the engine as shown in this photo.


06-11-06, 08:25 PM
It's not set up like the older Deville Seville, etc.
Those would set a code and disable the system until it was repaired.
The CTS and most newer ones just use pressure switches, the system either works or it doesn't.
If it won't come on there is either a bad sensor or no refrigerant.
A scan tool is a good way to isolate the cause.
I would agree a visual inspection of the A/C lines and related sensors would be a good start.

06-12-06, 01:05 AM
Thanks for the info fellas...I checked the sensor, and was about to jump it 'till I saw the 3 prongs. I didn't have my multimeter at the time or I would have checked for the sending voltage.

I had plenty of pressure, ~150 on the equalized sides, so the compressor "should" have at least kick on.

The strange thing is that it has been working normally since I've had it with ZERO indication signals(poor performance, heavy cycling of the compressor), it just quit. :confused:

I was about to check the fuses, but I'm going to take it into the dealer and let them figure it out...I need a few other things done anyway.

I'll update with what it was if I talk to them about it(my salesman is the middleman and I don't always get the info).

06-16-06, 12:49 PM
I picked the V up two days ago, A/C is working fine. I heard two explanations, one was that a wire melted :eek:, and the other is that the external temp probe went out. The latter is probably what happened as my Z06 buddy had this happen to him. Why GM would make A/C operation depend so much on the outside temp is beyond me. Why do I care what the outside temp is when it's 900 degrees in the car!! :rant2:

06-16-06, 01:48 PM
If it's too cold outside they disable compressor operation.
I forget the rationale, but I am sure it has to do with evaporator icing.

06-16-06, 02:19 PM
If it's too cold outside they disable compressor operation.
I forget the rationale, but I am sure it has to do with evaporator icing.

similar thing happened to my dad when he picked up a new 2000 C5, the A/C would work, why you ask the car thought it was -25 outside. they did some reset procedure that involved driving the vehicle at 20mph for like a minute.