The 2008 Volvo XC90, particularly the V8 model, is known to experience problems with its air conditioning (AC) system, specifically related to the variable displacement compressor and its solenoid. This article delves into the common issues, symptoms, and potential solutions.
Understanding the Variable Displacement Compressor
All V8 XC90s utilize a variable displacement compressor, featuring a solenoid controlled by the Engine Control Module (ECM) to regulate pressure within the compressor crankcase. This solenoid adjusts the compressor’s pumping capacity based on cooling demands.
Common 08 Volvo XC90 AC Problems
A frequent issue is solenoid failure, leading to reduced or complete loss of compressor pumping capacity. A sticking solenoid can prevent the compressor from building pressure, resulting in insufficient cooling. A telltale sign of this issue is intermittent AC failure, particularly after the engine has warmed up. Heat expansion can temporarily free a sticking solenoid, restoring functionality until the compressor cools down again.
Diagnosing High Side Pressure
High side AC pressure in the XC90 is influenced by ambient temperature, humidity, and engine speed. Following standard AC diagnostic procedures (1200-1500 RPM, fan speed one notch below maximum, recirculation enabled) can reveal pressures nearing 300 psi on a properly functioning system during hot and humid conditions. Systems with dual evaporators will also exhibit higher high side pressures.
Obstructed condenser airflow or faulty condenser fans can contribute to abnormally high pressures. Once the cabin cools, target pressures should be around 30 psi (low side) and 180 psi (high side). However, with a variable displacement compressor, these pressures can fluctuate.
These compressors often possess higher capacity, enabling efficient cooling at idle with full solenoid engagement. Compressor capacity diminishes below 1200 RPM, explaining why AC performance suffers in stop-and-go traffic or at idle.
As the evaporator temperature decreases, detected by the evaporator discharge air temperature sensor, the ECM reduces the signal to the compressor solenoid, decreasing pumping capacity. In a well-cooled vehicle with reduced fan speed, pressures can drop to 48/150 psi. The system prevents evaporator temperature from falling below 3-5 degrees Celsius to prevent freezing.
Evaporator Temperature Probe
While generally reliable, evaporator temperature probes can malfunction, though rarely. However, complete AC failure for extended periods, such as 10 minutes, points strongly towards a sticking solenoid. This intermittent cooling failure is a key indicator of solenoid problems.
