I have a 2005 jeep wrangler SE. It only blows on the 4 setting and doesn't when the fan is on one, two or three. What's up?

Blower Motor Resistor: Testing and Inspection
Warning: On vehicles equipped with air bags, disable the airbag system before attempting any steering wheel, steering column, or instrument panel component diagnosis or service. Disconnect and isolate the battery negative (Ground) cable, then wait two minutes for the airbag system capacitor to discharge before performing further diagnosis or service. This is the only way to disable the air bag system. Failure to take the proper pre-cautions could result in accidental air bag deployment and possible personal injury.

For circuit descriptions and diagrams, refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, further details on wire harness routing and retention, as well as pin-out and location views for the various wire harness connectors, splices and grounds.

1. Disconnect and isolate the battery negative cable.
2. Remove the glove box from the instrument panel.
3. Disconnect the wire harness connector from the blower motor resistor block.
4. Check for continuity between each of the blower motor switch input terminals of the resistor and the resistor output terminal. In each case there should be continuity. If OK, repair the wire harness circuits between the blower motor switch and the blower motor resistor, blower motor or blower motor relay as required. If not OK, replace the faulty blower motor resitor block.

How to replace the blower motor resistor block:

Caution: Stay clear of the blower motor and resistor block (Hot). Do not operate the blower motor with the resistor block removed.

1. Disconnect and isolate the battery negative cable.
2. Remove the glove box from the instrument panel.
3. Pull out the lock on the blower motor resistor wire harness connector to unlock the connector latch.
4. Depress the latch on the blower motor resistor wire harness connector and disconnect the connector from the resistor.
5. Remove the two screws that secure the blower motor resistor block to the HVAC housing.
6. Remove the resistor block from the HVAC housing.

Installation:
1. Position the blower motor resistor block into the HVAC housing.
2. Install the two screws that secure the resistor block to the HVAC housing. Tighten the screws to 2.2 Nm (20 in. lbs.)
3. Connect the wire harness connector to the resistor block.
4. Push in the lock on the blower motor resistor wire harness connecgtor to lock the connector latch.
5. Install the glove box.
6. Reconnect the battery negative cable.
7. Have a nice day!