Hot wires powering blower motor

Nissan sentra 1994. Just replaced melted blower motor speed control switch. The maximum speed switch setting contacts were melted into the plastic switch enclosure. After replacing the switch the wires coming into the switch and going out to the motor are very hot, burning my fingers... I have checked the motor, it draws about 15Amps from battery when engine is not moving (12V). It could be not accurate measurement since I lost some power on multimeter probe contacts at such high currents...

Is this a normal current draw for the blower motor in a small car like sentra? What can I do about overheating wires ? The wires do not look thick enough for 15A currents running through them. Also, the socket/plug for the motor speed switch contains regular-looking quickconnects, is it possible to disassemble the switch receptacle and replace/rework new quickconnects ?

Reply to
Pszemol
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bad relay

Reply to
tudysmuck

what relay ? I do not think I have a relay at the blower motor circuit.

Reply to
Pszemol

"Pszemol" writes in article dated Thu, 18 Aug 2005 10:29:21 -0500:

15A is too high. My guess would be 1A on the maximum setting. Try replacing the blower motor.

-- spud_demon -at- thundermaker.net The above may not (yet) represent the opinions of my employer.

Reply to
Spud Demon

To eliminate our guessing what current is normal, maybe a look at the blower motor fuse holder or fuse panel cover to see what it calls for will nail it down. s

Reply to
sdlomi2

How would you explain this method of testing? My motor consumes 15A. If the fuse is 20A what does it tell me ? If the fuse is 10A it would not work, would'nt it? It would blow the fuse.

I did check one more thing - the wires seem to be extremelly hot next to the speed switch receptacle and considerably cooler when I touch them further away from the switch receptacle. It does tell me that I have the corroded contacts problem. Looks like the quick connects in the receptacle have too high contact resistance, which at 15A produces a lot of heat to dissipate into the wire.

How to fix it ? I have no idea... It would be very hard to get the new plug/receptacle and rework all the connections properly...

Reply to
Pszemol

15Ax12V = 180W. Is it really too high current? Your vacuum cleaner consumes 12 or more Amps at 120V - of course the power factor is probably close to 1/2 but still - it is about 700-900W power consumption for a vacuum cleaner motor...
Reply to
Pszemol

As you already inferred, the wire being cool enough but the switch being too hot indicates switch-problems. Sounds like you have the problem spelled out, the problem being inside the switch. (Still a possibility the motor itself is dragging/pulling too much current. BUT the wire itself being cool...) I've by-passed original switches with a universal, variable-resistor type switch--be sure to mount it where its backside is near NOTHING and where a child cannot reach the backside, as it gets esp. hot on the lower speeds and will literally BURN your hands!!!. That's why factory voltage-dropping resistors are mounted inside the blower-box under the hood--away from hands and in the line of air-flow to dissipate the heat. To answer another question you asked: If the fuse-box calls for a

20-amp, yes it will blow fuses if you try to limit current using a smaller capacity fuse, like the 10-amp you mentioned. HTH & good luck. s
Reply to
sdlomi2

The switch itself is new, from the dealer. The original melted away. Check the FIRST sentence in my original posting...

The connector/receptacle accepting the switch is old, on the original electric harness - not replaceable unless I cut the wires and crimp another set of quick connects.

?? The fuse does not limit the current, resistor does. The fuse breaks the circuit when the current is too big. Assuming my motor works with the original fuse, the current is not too big. At least not too big to blow the fuse.

So once again, I do not understand what could I tell looking at the fuse type/rating.

Reply to
Pszemol

I only mentioned that because there seemed to be some guessing by other posters about how much current it was supposed to draw--like as low as 1 amp . Your grasp on this topic seemed always on target, and I merely wanted to reaffirm YOU were correct & not to be dissuaded by some others' incorrect guesses & miscalculations. I'm sure we both agree that if the mfg. called for a 20-amp fuse in this circuit, then they expected to protect a maximum draw of close to but somewhat less than 20 amps--definitely not 1 amp as I believe another poster supposed. Hopefully the contact spray you mentioned will heal the problem. I now realize the switch is new, and the connector/receptacle seems to be where the excessive resistance lies. This part would be bypassed, as described earlier, by running a separate fuse-protected wire, with a var'l.-resistor type switch in-line, to the blower motor & dis-connecting the original wire to the motor. Might save having to cut and install quick-connects on a bunch of hard-to-access wires. s

Reply to
sdlomi2

If you are replacing parts without tracing down the cause I would STRONGLY suggest that you let someone with the proper tools and training trace down the cause before you start an electrical fire. I would not rely on the by-guess-by-golly information you have gotten so far.

Reply to
John S.

My Jeep went like that so I just cut the plug off and put new ends on each wire and individually plugged each wire onto the switch. It works great.

Just leave an inch of wire or so coming out of the plug so you have a color code to rewire it in the right place.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
Reply to
Mike Romain

I will probably have to do it this way, because the original plastic receptacle is melted in the place where the high speed connection is. I would not be able to reuse this shroud to put new quick connect in.

The car is at the end of its life anyway... it is 1994 sentra with 130k miles. It is unlikely anybody would buy this car from me for other reason than a junkyard parts supply ;-)

Reply to
Pszemol

I have driven a 'lot' of old beaters and wired a few switches like that including headlight switches that melted down the plug just like you are seeing. I even have the headlights on my Jeep wired with their own rocker switch because of a hot spot like that. The running lights still use the factory switch.

It works really well and I now have very bright headlights. That hot spot was eating power up in heat so my headlights, even with a new switch, were yellow beams. It 'sure' is nice to have bright white lights again!

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
Reply to
Mike Romain

I checked this today, and it was enough to spray it with the contact cleaner from RadioShack. The wires are now still little warm to touch but they do not burn my fingers anymore. I think I will refrain from redoing the plug at this point and put the front dash/column back together. I am tired of driving with the car disassembled for days :-)

Reply to
Pszemol

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