Checked four Changeair heat pump units #8, #13, #14 and #16 for no cool. Found #16 tripping off on high pressure due to no condenser fan operation. Found the ecm on the condenser fan not receiving the proper 2-10 vdc signal to run. Found the plug in the condenser section for the dc signal failed. Removed the plug and direct connected the wires. Started the unit and verified operation. Found the other three units with the same issue. Removed the plugs and direct connected the wires. Verified operation. Took pictures and sent the failed plugs to the service department at Changeair per their request.