Today I got into my truck and the a/c would blow just fine but would not cool. I stopped and got some fuel, jumped back in my truck. And tried to turn on the a/c again. It will turn off and immediatly turn back off again. It just cycles like this until I press the off button. The entire display turns off, not just the fan BTW. Is there a fuse or a relay that could be causing this or am I looking at facing bigger problems. Im hoping just a relay since I think one of my coil packs is going out as well (engine bucks around 55-60mph).
This is on an 04 F150 Lariat with the automatic a/c controls.
Have you done any work under your dash to the immediate right of the steering column? That's where the interior temp sensor and vacuum hose is located. If that sensor goes bad or the hose gets crimped the A/C unit will get bad info and behave erratically. Here's some helpful info from the service manual you can try...
Electronic Automatic Temperature Control Module On-Demand Self-Test The EATC module on-demand self-test will retrieve on-demand (hard fault) DTCs only, it will not retrieve continuous DTCs. Continuous DTCs can be cleared when exiting the EATC module on-demand self-test. Make sure to retrieve continuous DTCs by carrying out the Electronic Automatic Temperature Control Module - Retrieve Continuous DTCs procedure before clearing any continuous DTCs.
•The EATC module on-demand self-test will not detect concerns associated with data link messages like engine coolant temperature or vehicle speed signals. A diagnostic tool must be used to retrieve these concerns.
•The EATC module on-demand self-test will detect concerns in the system control functions and will display on-demand (hard fault) DTCs for concerns that are present during the self-test. The vehicle interior temperature should be between 4°-38°C (40°-100°F) when performing the self-test. If the temperatures are not within the specified ranges, false DTCs may be displayed.
•The self-test can be initiated after cycling the ignition switch from OFF to ON. Normal operation of the climate control system stops when the self-test is activated.
•To enter the self-test, press the OFF and DEFROST buttons simultaneously and release, then press the AUTO button within 2 seconds . The display will show a flashing blower icon for 20 seconds , after which all vacuum fluorescent segments will be displayed if there are no on-demand DTCs present. If DTCs are present the EATC module will display "00 00" and then on-demand DTCs. Record all DTCs displayed.
•If any DTCs appear during the self-test, carry out the diagnostic procedure. Refer to the Electronic Automatic Temperature Control Module Diagnostic Trouble Code Index and follow the ACTION for each DTC given. See: Diagnostic Trouble Code Descriptions
•If a condition exists but no DTCs appear during the self-test, GO to Symptom Chart Condition: The EATC System Is Inoperative, Intermittent or Incorrect Operation. See: Symptom Related Diagnostic Procedures
•To exit the self-test and retain all DTCs, press any button except DEFROST. The EATC module will exit the self-test and retain all DTCs.
•To exit the self-test and clear all DTCs, press the DEFROST button. The EATC module will exit the self-test and all DTCs will be cleared.
•Always exit the self-test before powering the system down (system turned OFF). Once the self-test is exited, the ignition switch must remain ON for at least 30 seconds to allow the door actuators to automatically recalibrate.
•Continuous DTCs will be deleted after 80 ignition switch ON cycles after the intermittent fault occurs.
Electronic Automatic Temperature Control Module - Retrieve Continuous DTCs
The EATC module will retrieve only continuous (intermittent and hard) DTCs when carrying out this procedure.
•Retrieval of continuous DTCs can be initiated after cycling the ignition switch from OFF to ON. Normal operation of the climate control system stops when retrieving continuous DTCs.
•To retrieve continuous DTCs, press the OFF and DEFROST buttons simultaneously and release, then press the RECIRC button within 2 seconds . All vacuum fluorescent segments will be displayed if there are no continuous DTCs present. Continuous DTCs are indicated by the presence of the degrees Celsius symbol (°C) on the EATC module display. Record all DTCs displayed.
•If any DTCs appear, carry out the diagnostic procedure. Refer to the Electronic Automatic Temperature Control Module Diagnostic Trouble Code Index and follow the ACTION for each DTC given. See: Diagnostic Trouble Code Descriptions
•If a condition exists but no DTCs appear, GO to Symptom Chart Condition: The EATC System Is Inoperative, Intermittent or Incorrect Operation. See: Symptom Related Diagnostic Procedures
•To exit and retain all continuous DTCs, press any button except DEFROST. The EATC module will exit the retrieved continuous DTCs mode and retain all continuous DTCs.
•To exit and clear all continuous DTCs, press the DEFROST button. The EATC module will exit the retrieve continuous DTCs mode and all continuous DTCs will be cleared.
•Always exit the procedure before powering the system down (system turned OFF). Once the procedure is exited, the ignition switch must remain ON for at least 30 seconds to allow the door actuators to automatically recalibrate.
•Continuous DTCs will be deleted after 80 ignition switch ON cycles after the intermittent fault occurs.
Electronic Automatic Temperature Control (EATC) Module and Electronic Manual Temperature Control (EMTC) Module Cold Boot Process The purpose of the cold boot process is to allow the EATC or EMTC module to re-initialize and calibrate the door actuators. To carry out the cold boot process, follow the steps below.
1.Turn the ignition switch to the OFF position.
2.Disconnect the EATC or EMTC module electrical connectors.
3.Wait one minute .
4.Connect the EATC or EMTC module electrical connectors.
5.Turn the ignition switch to the ON position.
6.Select any position except OFF on the EATC or EMTC module. The EATC or EMTC module will now initialize and calibrate the mode doors. Calibration of the mode doors will take approximately 30 seconds .
This forum is owned and operated by Internet Brands, Inc., a Delaware corporation. It is not authorized or endorsed by the Ford Motor Company and is not affiliated with the Ford Motor Company or its related companies in any way. Ford® is a registered trademark of the Ford Motor Company
... you know who you are. 
Linear Mode
