No. If the fan is off during the day, the shield will suffer from radiation loading, and the thermocouple will measure a higher ambient air temperature. If the fan is off during the night, under clear sky conditions, the ASPTC-L shield will emit long-wave radiation and cool to a temperature lower than ambient air temperature. Consequently, the thermocouple will measure a lower ambient air temperature. Running the fan and aspirating the thermocouple ensures that it is measuring ambient air temperature.
If the site temperature is expected to fall below -10°C, consider using a naturally aspirated fine-wire thermocouple, such as the FW3, FW1, or FW05, in combination with the FWTM Fine-Wire-Thermocouple Mount and the FWC-L Connector Cable for Fine Wire Thermocouples.