Evap core freezing up?

[mk378]

A variable displacement compressor is supposed to never pump the evaporator pressure below where R-134a vaporizes at 32F, so there is no way that ice can form on the coil.

The design requires that the refrigerant be pure R-134a. Contamination with air will reduce the partial pressure to the point where freezing can occur.

 

[nthach]

The AC control logic should either disengage the compressor clutch or put the compressor into a low volume mode if it detects a frozen evap. More than likely the climate control system will display a system fault.

I'm thinking air in the refrigerant circuit, restriction in the expansion valve or it could be a dirty cabin filter.

 

[SHOZ]

I'd be checking the evap sensor with a volt meter. They are resistive devices and any change will throw off the output. Might be able to fix it by simply unplugging it and plugging it back in. But if it's freezing over that is a pretty good sign that's where the problem is.