You need to check the pressure. Many times a system will ice when it is on the verge of an underchargem it may be leaking ( and a year is about right for most improperly sealed ac systems to have done a fair amount of leaking... if pag or ester oil was used on the orings instead of mineral oil or Nylog, you can bet money that the system leaked at every fittin... I make good money going after folks and repairing those mistakes :-)

Once you get the overall pressures straight, if the low side is cutting out too low when on recirculating with the fan on low for a while ( you shouldnt see center duct temps any colder than 33 deg and with it set as mentioned, low side should cut out around 20 psi, 18 lowest, have a big box fan blowing across the condenser while testing., if duct temps too cold or cutout too lowm your accumulator switch should have a little screw in the middle of it when you take the plug off, you can adjust that screw to alter the cutout pressure up or down turning it up will stop icing( it gets colder as the pressure drops) you want to turn it up till the duct temp with the fan on low recirculating will not drop below 33 deg, if you got an aftermarket switch with no screwm and you have a cutout pressure issue, you will just need to replace the switch, make sure to get one for r134a
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-------Robert,:'00 XC70. '95 960, '93 940t, '90 240 wagon, '94 940SE, '84 240 diesel (she's sick) , '80 245 diesel, '86 740 GLE turbo diesel, '92 Ford F350 diesel dually

Does the air flow also diminish in force through your vents when this happens?
To me, you described a frosty coil.

If so, it appears you are icing up on the evaporator which means the low pressure switch is running the too long. This system does not have a separate "deicing switch" to sense the coil that other car systems in the past had. This system monitors pressure only.
Yes, the car may have worked earlier, in the last year, but the humidity can change or the switch its self may have move from its factory setting after several cycles.

In setting, I mean two things. Its original set point or the differential spread may not be wide enough to allow defrosting to keep it from frosting up in your case.

There is an adjustment between the prongs on the switch to raise or lower the set point of the low side pressure. Just raising the pressure a few pounds raise the coils temperature several degrees.
Gage's should be used to observe any changes done to the switch.

The screw changes the spring tension inside in relation to the low side pressure and the movement of it is not much to create several pounds change. Probably less than a one-eighth turn, I think, clockwise will be plenty, if not too much as I remember! They can build this switch both ways to click off or on, with rise or fall of pressure. Good to have a set of gauges for this reason.

The differential is not an adjustment that can be altered. Replacing the switch is the only option. That can be done without loss of refrigerant as there is a schrader valve under the switch connection.

Good luck at dialing it in for your climate.
Phil

verify your ac cooling fan is coming on