Heat/AC Blower fan speed only works on High

check fuses, then wiggle speed control while moving, may need new dash control for lower speed, usually high speed works through relay may be the reason high speed works

Hey! Oddly enough, mine started with the same thing this morning. I Googled the heck out of this and I'm more than satisfied that the most likely culprit is the blower resistor. This is EXCELLENT how-to guide (with lots of positive results): http://bvensko.blogspot.com/2008/02/how-to-repair-jeep-grand-cherokee.html

I would try to replace the blower motor resistor first,If that doesnt repair your problem you may wanna try replacing the blower speed switch.The resistor is located under the passenger side of the dash mounted in the heater box.

Blower resistor. Thats how you get different speeds

I'd check the relay and the resistor ...don't have a location for yours but the resistor is always installed into the heater box so it stays cool. you can usually follow the wiring back to the relay as it's generally nearby. Resistor looks like a piece of circuit board material with several wires connected to it with two screws holding it to the heater box so it sits flush except for the wires. It has several coils inside...any that are broken have failed.

Check the blower motor speed dropping resistor pack and it's connections. It is located in the ducting airflow of the blower motor.

U need to replace the blower motor speed control resistor.

The blower motor works on high setting ONLY when the blower resistor is bad. The blower motor resistor is held in place with 2 screws and attached into the heater housing under the right side of the dashboard. You can identify the resistor by the big wires that are connected to the connector. If this heating/cooling system is the auto temp type, the part is a bit high on the price.

Alot of people have the same problem with the fan switch and blown bulbs. There really is no fix for this. Jeep really screwed up when designing the heater control assembly. The cheapest solution is to buy another unit off Ebay. Can always go to the dealer but be ready to PAY for there mistakes.

Well, the blower resistor handles the lower speeds and the hi-blower relay handles the hi speed only. if the fan still works on the lower speeds then the resistor is bad. if the fan doesn't work at all then your motor has failed and or burn't the relay out also. if you can get your blower to start by hitting the kick panel above the pass. side foot area then the motor is bad. if you are handy enough to drop the kick panel and access the motor then check the connections at the motor. Then wack the motor and see if it comes on then. you will most likely find the problem if you follow those simple rules above. Good luck.