Be sure to check power on both side of the fuse!. I had the same problem and found the fuse connection not making good contact in the holder and it caused the same problem of no clutch engaugement. I think your 300D has the temp control thermostat knob on the console. Check to see if there is power at the switch after checking the fuse. I think also the power is distributed by the vacuum relay switch as well so check to see if the a/c heat is switches over properly. Someone please correct me if I am wrong!
Regards,
Bryan