Properly Testing Bladed Thermal Fuses

When testing bladed thermal fuses for an open or incomplete circuit, it’s critical to follow the proper procedures as outlined in the appropriate Service Information to reach a correct diagnosis and avoid damage to the electrical center. (Fig. 10)

 

Fig. 10

 

Testing a Fuse

To determine if a bladed fuse is open and needs to be replaced, do not remove the fuse as the first step of diagnosis. Instead, check the continuity of the bladed fuse using a Digital Multimeter (DMM) or a continuity tester (test lamp) by testing at the test points at the top of the fuse. (Fig. 11)

Refer to Circuit Protection – Fuses in the appropriate Service Information.

 

Fig. 11

 

Fuse Removal

If the Digital Multimeter reads an open circuit, or the test lamp does not light up, replace the fuse with one with an equal current rating. Be sure to use the recommended fuse puller tool in order to prevent any damage to the fuse or the terminals when removing small fuses. (Fig. 12) Check the Owner’s Manual for the location of the fuse puller tool.

Improper removal of the fuse, such as by moving the fuse from side to side, may cause damage to the internal terminals or tuning forks that retain the fuse, leading to intermittent conditions within the electrical center.

Fig. 12

 

For the correct current rating when replacing a damaged fuse, refer to the appropriate Service Information.

Following the proper fuse testing procedures will help avoid potential damage, which may cause intermittent conditions or complete failure of the electrical system.

 

– Thanks to Mike Bray