Need electrical help

[Eagle]

Mice built another nest in the heater airbox of my 2000 XJ, causing the fan speed resistor pack to overheat and burn out the thermal fuse. EagleScout is getting me a replacement, but those things aren't cheap. I have a growing collection of them that could be repaired by soldring in a replacement thermal fuse.

 

If I knew what rating fuse to use.

 

And if I knew where to get the thermal fuses.

 

Can anyone help? @Ωhm are you there? Paging Dr. Ohm, to the yellow courtesy phone, please.

[Eagle]

Found a very old thread in which Jim Oshell pointed to the old XJ FSM schematic, which showed the thermal fuse with a rating of 149 degrees C. I haven't had any luck finding that exact rating, but Amazon has some at 142 degrees and 157 degrees. At 70 cents per fuse for a pack of ten, I'll try them.

 

https://www.amazon.com/BOJACK-Thermal-Degrees-Celsius-Cutoffs/dp/B07Y62XXZX/ref=sims_dp_d_dex_ai_speed_loc_touchpoints_mtl_t2_d_sccl_3_2/131-2691869-6617666?pd_rd_w=O4wO0&content-id=amzn1.sym.b60dadd9-7f9e-4256-887b-3cfe6cc8c59d&pf_rd_p=b60dadd9-7f9e-4256-887b-3cfe6cc8c59d&pf_rd_r=ST8JHMKR59Q6THH6NN7X&pd_rd_wg=iCKjc&pd_rd_r=8f37e6dc-d0ee-47f6-afc1-d8a8cb49a505&pd_rd_i=B07Y62XXZX&psc=1

 

The plan now is to repair all the old ones I have had to remove, replace the thermal fuses, and keep 'em as spares.

[Ωhm]

@Eagle  Yeah, 88electrical manual show 149C(300F) for thermo cutoff. Voltage drops are used for Headlamp SW dimmer, ballast resistor (4L) and the big one (lots of HEAT), Blower Motor Speed. Hope you get what you're looking for.

[Eagle]

Thanks.

 

I have ordered 10-packs of the 142- and 157-degree thermal limiters from Amazon. Once they arrive I'll have to se if I can get the outer cover off to access the terminals for soldering in the new fuse, and hope for the best.

[Eagle_SX4]

After you get all the mouse nest cleaned out make sure your blower motor is good.

 

I blew 2 of those blower resistor packs before I realized that my blower motor was drawing to much current. I swapped my blower motor and haven't had any issues since. 

[Eagle]

Blower motor works on high speed. Not a problem. I just need a new resistor pack, which is on the way.

 

When the thermal fuses arrive from Amazon, since I couldn't match the 149 degree rating, I have to choose between slightly under and slightly over. I'm thinking I'll try 142 degrees first. Is that likely to cause a rapid failure (absent another mouse nest, of course)? Any reason why I should go directly to a 157 degree thermal fuse?

[Ωhm]

Treat it like a fusible link, start low (142°C). Keep in mind what @Eagle_SX4 said. DC Motors that turn slow/slower (rpm's) can't create counter voltage, causing increased current flow in the circuit.

[gogmorgo]

As a rule you don't set a fuse at barely above normal condition, and 7°C isn't that much of a jump, especially considering that's still well over the boiling point of water. I'd be more concerned about exceeding the designed fuse temp and going with the 157.

[Eagle]

It actually IS like a fusible link. In fact, it's more often referred to as a "thermal limiter" than as a "fuse." It's purpose isn't to respond to over-current, it's to protect against over-temperature.

[gogmorgo]

Arguably that's what regular fuses do too. When they overheat they disconnect the circuit.