I don't know which model do you have but flashing snowflake usually means that the compressor is in the lockout mode (i.e. the indoor coil is likely frozen and there's too much pressure in the system to start the compressor). See the display pages from a manual for White Rogers (Emerson now) 1E78 thermostat.
Try to power the AC off for 45 minutes to an hour so the indoor coil can thaw. It would not hurt to verify that the drain is clean at this point, by the way, because there will be a lot of water trying to escape from under the coil. While it's thawing, check the AC filter for if it's dirty, the airflow will be restricted and the coil with freeze again. Any other airflow restriction will do the same.
There may also me refrigerant leak - these are a common reason for indoor coil freeze ups. You will need an HVAC technician to verify that. So, thaw, check filter and if it repeats, call an HVAC tech.
- posted 7 years ago