What makes my cars a/c line freeze with ice and the air stops blowing?

Question

a/c clutch cycling switch

a/c clutch relay

a/c pressure sensor

a/c expansion valve

a/c evaporator temp sensor

Answer 1

It depends where in the system the freeze up is occuring. But ice will develop when there is a restriction. The pressure drop across the restriction causes the refrigerant to change state and give off heat. Ice forms and blocks off the refrigerant flow completely. If it's near the low pressure sensor that will shut the AC system down completely until the ice melts and the blockage clears.

That is exactly what happens at the inlet to the evaporator in a properly working system. Liquid refrigerant goes through a restriction. The pressure drops and the liquid boils, giving off heat. The fan blows across the evaporator and the air is cooled in the process.

It could also be caused by moisture in the system. It may need to be evacuated and recharged to correct the condition.

Answer 2

evaporator temp sensor and expansion valve together.

A by product of the cold evaporator is the water in the air freezes on the evaporator, building up a layer of ice. The evaporator temp sensor (in most cars it is a wet bulb with a tiny tube that runs to the expansion valve) gets too cold, it closes the expansion valve, cutting off the freon.  This allows the evaporator to warm up (from warm air), warming the wet bulb, which reopens the valve.  This cycling makes the evaporator self-defrosting.

You didn't say what type of car.  Older cars, the systems are mechanical.  Newer cars, the systems are electronic.

Answer 3

If you tried to charge it yourself, it is possible to over-charge the system. The system is equipped with a LOW pressure switch, and some have an OVER pressure release valve. However if it is over charged it will freeze the lines.