This investigation was opened based on one complaint and reports from four transportation fleets alleging 182 blower motor control switch failures.ODI was concerned that these melting and burning switches could lead to an open flame that could spread throughout the vehicle.After a comprehensive review of all data related to overheating blower motor control switches in the subject vehicles, ODI did not identify the existence of a safety defect trend.ODI reviewed 1,036 complaints, claims, and field reports of failed blower motor control switches and determined that only two fires were likely to have been caused by a failing subject blower motor control switch.This represents a failure rate of 0.2 R/100K on a population of 1,076,975 vehicles that have been in service for up to 14 years.ODI has found that when the subject switches do fail and begin to melt, they are constructed in a manner that typically prevents the failing switch from igniting and developing into an open flame.Ford Motor Company has agreed to take two actions to further reduce the likelihood an overheated blower motor switch in the subject vehicles.Ford informed ODI that it has implemented a series of design changes to the subject switch that will help prevent it from developing internal high resistance short circuits.Ford has also informed ODI that it would release a Technical Service Bulletin (TSB-11-11-21) instructing subject vehicle owners to replace the electrical connector at the same time a failed switch is replaced.In light of the low rate of failure resulting in open flame and fire spread on the subject vehicles, and Ford's actions to reduce the likelihood of a switch failure through switch design changes and a TSB, further use of agency resources does not appear to be warranted.The closing of this investigation does not constitute a finding by NHTSA that no safety-related defect exists.The agency reserves the right to take further action if warranted by the circumstances.The ODI complaints cited above can be reviewed at www-odi.nhtsa.dot.gov/owners/SearchNHTSAID under the following (ODI) numbers: 10427875, 10114393, 10257890For additional information, see the attached closing report.
