# problem with air conditioning



## zbynior (Sep 28, 2012)

Hi 
I have a small problem with the air conditioning
can I turn off the air conditioning, which automatic turns on when I switch the air on front glass
chevrolet services says that there is no option unfortunately: (

regards 
zbynior from poland


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## jblackburn (Apr 14, 2012)

No. The AC turns on with defrost to dehumidify the air in the car. Humidity causes condensation on the glass. 

The AC won't run the compressor below 40-45 degrees F or some number around that. So if its cold outside, it's not running anyway.


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## OnlyTaurus (Mar 20, 2012)

jblackburn said:


> No. The AC turns on with defrost to dehumidify the air in the car. Humidity causes condensation on the glass.
> 
> The AC won't run the compressor below 40-45 degrees F or some number around that. So if its cold outside, it's not running anyway.


Its not the ambient air that will disable the A/C compressor, its the thermistor in the evaporator. Though air temp does play part in it of course.
*
Evaporator Temperature Sensor*

The evaporator temperature sensor is a 2-wire negative temperature co-efficient thermistor. The sensor operates within a temperature range of −40 to +85°C (−40 to +185°F). The sensor is installed at the evaporator and measures its temperature. If the temperature drops under 3°C (38°F), the compressor will be switched off in order to prevent a frozen evaporator.


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## v8318cid (Oct 3, 2012)

There is a second sensor to consider here. The system also has a pressure switch installed on the high pressure (liquid) line that runs along the passenger side fender wall. This switch (not sure if just low, or possibly trinary switch which also monitors for a high pressure condition) is responsible for monitoring the system pressure. As the outside temperature drops, the pressure in the system also drops. At approximately 40F, the pressure in the system will drop to a level that will activate the low pressure switch (assume below 20-25 PSI on a low side sensor, around 50-70 PSI on a high side sensor), which disables the compressor. This switch operates on pressure rather than temperature, although some systems also use the ambient/outside temperature sensor (usually located near the front grille although this is subject to model variations) to regulate compressor operation. I had a Cadillac DTS that would consistently shut down the compressor at an outside temp of 32F regardless of operating pressure.


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