E350 XLT 2014 Front AC works on High only
 

Front AC runs on high only, Rear AC has no issues. I have replaced these components twice with genuine Motorcraft Parts. Blower Motor Resistor, Switch on the Dashboard, and Blower Motor Relay. I have also checked the connectors on the switch for melting, burnt, corrosion, etc and have also checked for this on the Resistor End. Wires look good. AC blows cold. Any help appreciated, thanks