Heater blower on van won't come on. Already replaced heater blower and checked fuses.

How long ago was that heater blower replaced?
Well .....you have the relay , the on/off /speeds switch, and the circuit it self. I suggest you get the shop Manual for the vehicle and perform the simple testing needed for this circuit. Good luck

Check blower motor resistor make sure none of the spring's are broken, resistor sit next to blower motor in housing, also check blower motor relay for voltage, also sit over by blower motor outside of housing and last check voltage at blower motor switch.Hope this was very helpful,good luck.