Fan motor problem

The blower motor relay is energized when the Blower Motor Control is set to the High position. This removes the blower motor resistors from the circuit and battery voltage is then applied directly from the HVAC BLO fuse (RH IP Accessory Wiring Junction Block) to the blower motor though the relay switch contacts. The blower motor then runs at high speed.

HVAC Blower Controls Circuit Description
The blower motor is a variable speed motor. The motor operates at a higher rate when voltage is increased to the maximum level.
The blower motor resistors reduce the voltage supplied from the A/C FAN fuse (LH IP Accessory Wiring Junction Block) when the blower control is set at low and medium speeds (speeds 1-4). The blower motor relay is energized when the Blower Motor Control is set to the High position. This removes the blower motor resistors from the circuit and battery voltage is then applied directly from the HVAC BLO fuse (RH IP Accessory Wiring Junction Block) to the blower motor though the relay switch contacts. The blower motor then runs at high speed.

Try all fan speed settings to determine if you have air flow on any (particularly High speed). I don't know the specifics of your Echo, but typically high speed is a straight-through connection for power to the blower motor.
If high speed works but none of the slower speeds do, the issue is very likely the blower motor resistor or the resistor connector.
If none of the speeds work, there might be a bad fuse for the blower motor or the motor itself might be bad.
If you can hear the blower on all speeds but still no air is coming out the vents, the issue might be either a damaged diverter door that is not properly directing air flow or possibly something got sucked in to the blower motor squirrel cage and is severely restricting air flow. -Rod

The complete removal is shown in this youtube video.
http://www.youtube.com/watch?v=vLdMYx6fhic

So you're getting heat but no blower to circulate the heat, right? It's also possible the fuze is blown to the blower motor, the switch that adjusts the speed of the motor could be damaged, or its resistors that limit voltage, to control speed could be "open" (burned up). I would check many of those before replacing the fan..

The heat is controlled by a valve that allows water to circulate through the heater core. If the fan is blowing cold air, check the valve, or blow water back and forth through the heater core to clean it out.

I would replace the blower motor resistor first then see if that corrects this. The resistor is located next to the blower motor under the dash.

Check the wire connections at the blower motor and fan resistor, they are located under dash on passenger side. They sometimes have corrosion that burns the plastic connector. The resistor is responsible for all fan speeds below high. Hope this helps, let me know.

Most likely cause (common failure) is the blower motor resistor. On most caravans it is right behind the glove box with two 8mm head screws holding it in place

All cars are designed with a blower fan motor that pushes air through the ventilation system. This air is processed by a series of vents to direct the air to various positions. Example: heater, air conditioner and defrost modes. Most blower motors are power by a basic electrical circuit that utilizes a multi resistor or a solid-state resistor to control different fan speed modes (low, medium low, medium and high). If the resistor malfunctions it may lose one or more of the lower fan speed settings.
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you most likely have a bad airmix servo. this happens alot on these. they are expensive to replace too.

Sounds like a bad blower resistor

In many cases this is the result of the blower motor resistor having gone bad. They are often located in the housing that holds the blower motor but I cannot say 100% for sure with the Jeep Cherokee.