Low suction pressure freezing up evap on Volvo S80

[Swedal]

Trying to figure out why this Volvo S80 2003 never cuts out the AC compressor and why it has such a low suction pressure. AC works fine and cools very well but freezes up completley. I have evacuated and filled the system with 1000g R134a as label says. I suspected the evap temp sensor and removed it and did some meassurements and it seems to react as a thermistor. Maybe the ohm values are off? Well after some minutes of driving I have 17F (-8C) from the vents and ice is building up. Compressor never shuts off.

Question #1 Why the heck is suction pressure that low to even get such low temps from the vents?? I have never seen evap temps that low in a car.

#2 Why does the compressor not cycling on and off? Can I be sure it has to do with the evap temp sensor? I mean even if suction pressure is too low I would still have cut off from the compressor when evap temp is too low, right?

[charlie patt]

Suction pressure so low because it's freezing up
S series control coil temp by either evap coil sensor or lp switch depends on weather manual or digital ckimate you will need a scanner to read temp for suction evap sensor, first make sure clutch is free as prone to seizure and comp drives all the time thus constant cooling run it with ac on and press econ on dash you will hear a click and outer plate of clutch will stop spinning thus clutch good they are also prone if manual ac the relays in electrical box weld up together

[Swedal]

Thank you Charlie! I know about the clutch problem. Lots of old volvos with clutch issues. Works when cold but does not engage when cycling back on. This is not the case. Compressor runs all the time and I can disconnect it with AC-off button to de-ice it. When I have the evap temp sensor (OEM#30665118) I suppose its something wrong with this thermistor then. I tried to meassure ohms with different temps and it seems to work but maybe its off? I have not found a temp/ohm chart for it.

Can I rule out a clogged expansion valve? That too should cause low suction pressure. But then again, it should cycle of when getting too cold...

[charlie patt]

If expansion valve blocked you would have little cooling however most volvos on a orifice nowadays
If clutch shuts of on switch you have a control issue either poor resistance reading wrong you will need a scanner to read temperasure sensor is reading it's either that or its not fitting in its file correctly I pressume you have good air flow over coil and out vents not temperature but force of airflow

[terminator]

It does sound like the thermistor.
Either that, or the controller is interpreting the thermistor reading incorrectly.
Does it measure actual coil temp, or air on, or air off?