S80 Evaporator coil freezing

[ericandelia]

I have a 2002, S80 that after driving approximately 90 minutes the evaporator coil freezes. I am convinced it is frozen due to the loud blower (high speed) and lack of air coming out of the grills. I also opened the hood and found the suction line heavily frosted. I took the vehicle to a local repair shop and they performed their diagnostics.
The repair shop added only a few ounces of refrigerant and stated the sensors were verified via a computer. They stated the compressor had a fault and should be replaced. Due to the price and logic of the compressor being the root cause I declined the service. I did however speak directly to the mechanic and he stated the most probable cause of my coil freezing is the pressure switch. He stated the evaporator temperature sensor was working correctly and the pressure switch is a combination high/ low pressure switch.
Can someone please tell me if the pressure switch is actually a high/low pressure switch or is it just a high pressure switch? Also, would the pressure switch be the control to shut the compressor down when the evaporator coil gets too cold or would it be the evaporator temperature sensor?

Thanks in advance for your support, Eric

[jimmy57]

That S80 has an evaporator temp probe. The pressure switch is an input to the ECM for fan operation, low charge shut off, and excess pressure shut off. The pressure switch is on high side and can't be used for evaporator temp monitoring, the evap temp probe stuck in evap case above and the to right of accel pedal assembly does that job. If the probe is faulty or blocked due to having fuzz on it, it can make evaporator freeze. CCM reads that sensor and cycles compressor as needed.