The front heater blower does not blow but you can feel the heat if you put your hand on the vent. The back vent blows a/c but when you switch it to heat you can't feel heat but you can still hear the blower. What needs to be replaced?

Does the blower work at any speed? If it works on "high" then it is likely the blower resistor pack which is located in the heater box on the passenger side firewall. The blower motor could also be bad. The blower motor is located above the front passengers footwell, using a Digital Volt Meter check to see if it's getting a power and ground with the ignition on and the switch turned on. If you have both power and ground the blower motor will have to be replaced.

On the front blower make sure the fuse is ok if it is then check the relay if its good as well then youll ned to replace the blower motor. as far as the rear it sounds as if the air handler is not operating properly you need to locate it and ensure that nothing is blocking it from turning.hopes this helps you.