It is interesting to note how sophisticated automotive electronic climate control systems have become. Not long ago, I was reading a Volvo Service Bulletin that addressed normal operation of electronic climate control on a 2002 V70. A 2002 is not exactly a ‘new' vehicle, but, read on to see how complex things have already become.

This bulletin referenced many of the interesting inputs and outputs as well as the central processor that controls this system. Although these systems are very complex, all this modernization is really transparent and unknown by most vehicle owners and drivers. One of the items described was the Air Quality Sensor, (AQS). This sensor, mounted in the incoming air chimney, detects when outdoor air contains high concentrations of pollutants. When these pollutants are detected, the Climate Control Module, (CCM), transmits a signal to the fresh air/recirculate motor to close off outside air and go to recirculate mode. The level of recirculation is determined by the pollution level being detected by the AQS. Meaning that, if the pollution detection is slight, the motor will be commanded to just make a slight decrease to reduce ‘some' of the air coming in from outside. If heavy pollution levels are detected, the CCM will command ‘full recirculate' and minimal outside air will be drawn in. It is interesting to note that the CCM is also monitoring vehicle speed at this time. If vehicle speed is greater than 53 MPH, no change in outside air recirculation will be commanded. Also monitored is whether or not the driver has requested air conditioning and/or has turned on the windshield wipers. If either are turned on, the CCM will only allow recirculate for a maximum of 10 minutes, after which, the CCM will switch to fresh air. This is to prevent window fogging on humid or damp days. Also on that note, the CCM even monitors whether or not the driver has selected defrost mode. If so, again, recirculate will not be allowed so fogging is prevented.

The CCM also regulates the temperature in the passenger compartment based on several input signals, including: Passenger Compartment Temperature Sensor, Outside Temperature Sensor, A/C Evaporator Temperature Sensor and Sun Roof Status. The CCM will request the position of the sun roof from the Sun Roof Control Module via the vehicle's Controller Area Network, (CAN). The status of the Side Windows is also requested from the Driver's Door Module and Passenger's Door Module also communicating on the network. Door Status is requested from the Central Control Module via the network. Sun Intensity is monitored via the dashboard mounted Sun Load Sensor. As stated above, Vehicle Speed is monitored, as well as Windshield Wiper Status via the Steering Wheel Module also connected on the network.

If the CCM determines that side windows, doors or the sunroof are open, it will not compensate for temperature in the passenger's compartment. In this situation, the CCM will maintain the same level of climate control for air conditioning and blower fan speed as before the above items became ‘open'.

If the CCM detects strong levels of sunlight, the CCM will command a decrease in passenger compartment air temperature, change the distribution of air and increase blower fan speed.

If the CCM detects that the evaporator temperature has fallen below 43 degrees Fahrenheit, the air compressor operation will be halted to prevent evaporator freezing.

Finally, to maintain a constant flow of air in the passenger compartment, the CCM will use the Vehicle Speed Signal from the Brake Control Module to regulate the speed of the blower fan. Generally, as the speed of the vehicle increases, the speed of the blower fan will be decreased.

Overall, it just goes to show how just one system on a vehicle today can be so interconnected with other systems also onboard. After looking at Volvo's computer strategy above, one can easily see how a problem on one circuit can so easily affect another.  It's why diagnosing vehicle electronics can be a bit frustrating at times, but then again, you can't say it's not interesting work.