Blower resistor on mk1 Yaris

[flash22]

[Mooly]

Although the thermal fuse has a current rating (such as ten amp) it doesn't mean it is a ten amp fuse.

That rating means it can safely interrupt or break a current up to ten amps. It will pass 20 or 30 amps but if an over temperature causes it to trip then it can not safely break that higher current and the contact might self weld when it tries.

If the motor draws excess current then that will heat the resistor more and could reach the trip temperature of the fuse.

Put some numbers in. The green resistor has the values marked on it. Say the 1R4 section is in circuit and the motor pulls 3 amps. The resistor dissipates just over 12.5 watts as heat. If the motor is sticky and tries to pull 4 amps then the dissipation goes up to almost 22.5 watts, a massive increase in heat production.

In other words, a small increase in motor current increases the heat in the resistor much more than you might think.

    

 

 

[furtula]

I'll check the resistance when i get to replacing the fuse. They shipped the parts today.

The fan was working terribly slow on lowest setting, almost like it's off, not sure if it should be like that, don't have another Yaris to compare, but hopefully in next few days i will find out.

I did bridge the the fuse with a same gauge wire just for test, and it at first speed i'm not sure if it started at all, 2-3 were there, but noticeably slower than before, so it could be that fan slightly seized up, and  this was the causes of everything. Tried it few times for 5-6 seconds only. 

 

[Mooly]

Those symptoms do point to a motor drawing to much current (not as free to spin as it should be). That should be easy to check. Also possible would be some electrical issue like shorted turns on the armature windings which are not easy to test for.

If it spins freely by hand and still seems to pull to much current, then you're probably looking at a replacement motor unfortunately.

 

[furtula]

Got the fuse installed using small chocolate block connector, sawed in half. Makes for a tight fit, and can easily be replaced.

Tried it out and measured the temp.

On speed 1, it barely heated up, maybe around 20C, speed 2 was around 40-45 and speed 3 was around 50-60. This was without any cooling, just the resistor hanging outside, while i was measuring the temperature.  This was on the main block. The fuse did not get heated up so much.

Outside temp was 6 C.

Fan is much more loose now that it was working a bit, and can be turned by hand without much ressistance.

Hope i won't come back to this topic saying how the fuse blew again.

Fuse i used was 172C, 10A.

Mandatory pic:

 

[DerekHa]

Looks like your improvised repair of the thermal fuse and lubricating the bearings has done the trick Dean.

Hope it holds up for you now!

[Mooly]

35 minutes ago, furtula said:

Got the fuse installed using small chocolate block connector, sawed in half. Makes for a tight fit, and can easily be replaced.

That looks good. I like that.

So, it's all looking and sounding good so far...... excellent.