Need to replace blower fan

Change the blower motor resistor, or possibly the switch.

Bad connection at heater box under to hood

Remove the lower right silencer panel. Remove the electrical connector, it is plugged into the resistor. Then replace the resistor. Since the blower motor works on high speed it is most likely the resistor.

CHECK FOR VOLTAGE AT HEATER BLOWER MOTOR IF NOT YOU COULD HAVE A FAULTY BLOWER MOTOR RELAY.IF YOU HAVE VOLTAGE AT BLOWER MOTOR THEN BLOWER MOTOR FAULTY.

http://www.automotivehelper.com/topic294308.htm

This should be about the same.

the blower motor is either shot or there is something in the heater system touching the fan, remove the blower and bench test it, clean the housing and replace the resistor and motor if necessary

Just go on the passengers side under the dash and remove the insulator panel to see the blower motor.What usually happens is when it gets cold out critters from outside will work their way into your car and make a nest in the blower motor fan.This throws the fan out of balance and hence the vibration.Once you can see the blower motor then remove it.There are 3 or 4 screws.Hope this helps.Good luck.

The motor still works. A DC motor is speed controlled with a resistor. Luckily, the resistors that do this are mounted on the motor housing. See the following link. The resistor pack is quoted as costing about $10.
http://www.automotivehelper.com/topic294308.htm
Steve

First off, time for a thermostat change if not done recently. Where does your temperature gauge ride when at normal operating temperature? Same as usual, or lower? As far as fan goes, sounds like fan resistor has gone and will need to be replaced. I'll double check to see if it's an inline resistor, or part of blower motor & get back to you. Are you planning on attempting all this yourself?

You need to replace the blower motor resistor...