The A/C Heater Blower is working unreliably. The blower usually will not start after the engine has been turned on. Trying all the blower speeds, vent open or shut, A/C on, heater on does not result in the blower working. Then usually,after a few minutes or hours, the blower will come on. Sometimes after a bump in the road, sometimes not. when it does come on, it works in all speeds, and can be turned off for a minute, and turned on again. The blower sounds smooth in all speeds, and once running, will keep running. Can you suggest some trouble shooting? Resistor? Fuse? Relay block? Blower motor?