My 2013 ac was doing really well, blowing cold air and suddenly it would blow warm air. No matter what the temperature I set it to.

The fix for this is to replace the pressure sensor switch. You will need to remove the top plastic cover, use a 27mm socket to remove it. This switch is located in front of the radiator.
You will also need to vacuum all the refrigerants out first, then replace the switch. After that, need to recharge the AC system.

I searched this forum but did not see error code B1423

 

You sure the switch was bad? That code just means the pressure in the system is low probably due to not having enough freon. I got this code when I emptied out all the freon to change my heater core. Once I filled the system back up the code went away.

 

There was freon in the small glass window on the high pressure side before I replaced the switch.

 

That doesn't mean much. Did the shop check the pressure in the system with gauges? How much refrigerant was recovered from the system before you changed the switch?

 

It's doesn't matter at this point anymore, just trying to help someone out if they got the code. They replaced the switch and it's working great now.

 

Just to add in. I have a 2014 with the same B1423 error code. I bought an "AC recharge" kit thinking the R134a was low, but when I attached the unit the pressure reading spiked into the 'RED' zone. So I am going to replace this AC sensor. The Lexus PN for 2014 is (88719-33020). About ~$210 USD and a friend of mine has access to AC recharge machine. I'll report back and see what we find. My working theories:

1. the previous owner overcharged the system and now the system went into a "safe" mode. Just need to depressurize it (safely).
2. the sensor is actually bad and just needs to be replaced.
3. the compressor is bad and is continually compressing making the system over pressurized.

EDIT: I uncharged the system, (recovered .70 lbs for a 300k mile 2014 LS460 no rear AC, replaced the sensor right at the drivers side bumper (used a 27mm to get it off and 19mm to stabilize the mounting boss), then recharged the system (they put 1.3 lbs in). Now my AC works perfectly.