Blower fan runs slower than expected in cold weather (when in AUTO mode) (Climate Control)

Diagnostic Procedure 

Probable cause: Engine coolant temperature (ECT) circuit malfunction

Troubleshooting the ECT sensor circuit:

• ECT sensor 2 circuit low voltage
• ECT sensor 2 circuit high voltage

Also Check for 

• Climate control DTCs - Refer to: How to Troubleshoot the Body ElectricalHow to Troubleshoot the Climate Control System 
• PGM-FI DTCs - Refer to: How to Troubleshoot the Fuel and Emissions SystemsHow to Troubleshoot the CVT System(CVT System)
• Blower motor operation