There was a TSB for this. I don't have the number. Try removing the fuses per TSB. If it works, the seat module has to be reprogrammed by a dealer or it may stop working again. If it doesn't work, you're probably going to have to take it to a dealer and see what the codes are.
2007-2008 MKZ, Navigator
Some 2007-2008 Expedition and Navigator, 2006 Zephyr and 2007-2008 MKZ vehicles built before 8/31/2007 and equipped with climate control seats may exhibit inoperative heating and/or cooling. There are no diagnostic trouble codes (DTCs) associated with this issue and IDS/PDS will not communicate with the dual climate control seat module (DCSM).
Follow the Service Procedure steps to correct the condition.
- Turn the ignition switch to key on engine off (KOEO) position.
- Run self test on DCSM.
- If DTCs are present do not continue with this TSB, follow normal Workshop Manual (WSM) diagnostics for the DTCs.
- If no communication with the DCSM, proceed to Step 3.
- Remove power to the DCSM and wait a minimum of 2 minutes. This will reset the DCSM.
- Expedition/Navigator - remove Fuse 8 in the battery junction box (BJB).
- Zephyr/MKZ - remove Fuse 11 and 12 in the BJB.
- Reinstall the fuse(s) and recheck for communication.
- If communication does not return, refer to WSM, Section 418-00.
- If the communication is restored by resetting:
- Expedition/Navigator/2008 MKZ - reprogram the DCSM to the latest calibration using IDS release 51.4 or later with patch 7. Calibration files may also be obtained at www.motorcraft.com.
- 2006 Zephyr/2007 MKZ - replace the DCSM.
- Recheck operation of the heated/cooled seat and for DTCs. If no DTCs return the vehicle to the customer.