A/C blower motor wiring by-pass. (1 Viewer)

[g-man]

I wondered about this too. The resistor has 3 coils but only 2 coils reduce and go to the switch. So it looks like current flows through it even when the switch is on high. Easy enough to check.

My last test shows 14.2 amps at the power wire near the battery (my bypass wire). And 13.7 amps at the blower on high. Blower motor now testing at 11.31 volts. Gives me roughly 155 watts at the blower. Anyone happen to know what the rated watts are for the stock blower motor? I found nothing marked on the blower.

 

[Prairie Swamp]

I wondered about this too. The resistor has 3 coils but only 2 coils reduce and go to the switch. So it looks like current flows through it even when the switch is on high. Easy enough to check.

Interesting stuff. Looking at the circuit you posted - with the switch in Lo the only path for the blower to get power is to go through all three resistors in series - hence the lowest speed. In M1 and M2 the switch taps into the resistors at different places in that series bypassing some of the resistance. In Hi the switch gives the current a dead short path so it doesn't have to flow through the resistors.

Seems to me when I pulled the resistor on my FJ Cruiser the current in Hi did pass through the resistor assembly via a heavy copper trace in there. So this is not depicted correctly on the diagram as it shows a wire outside the resistor assembly.

V = Current X Resistance 11.31V/13.7A = 0.825 Ohms equivalent for the blower.

Sorry I don't know the rated amps.

 

[g-man]

pulled cleaned and tested the resistor. Before I pulled and cleaned these were the amps at the blue/red wire coming into the resistor from the blower:

Hi = .31 amps
M2= 9.27 amps
M1= 6.20 amps
Lo= 3.54 amps
off=3.55 amps ...seems my switch still pulls plenty even when in the off position

pulled and cleaned resistor:

Hi= .02 amps
M2= 9.33
M1=6.30
lo and off now reading .03 amps. I broke the rusty and very fine coil wire while pulling the unit from the a/c box.

New readings at the Alternator and blower motor:

Edit: Blower motor 13.31 amps
Alternator output 13.85 up from 13.7

New resistor ordered. Rockauto #20157. 32.99 plus 2.99 shipping. This thing is just too flimsy to try and clean esp since the wires are badly worn.

New 10g marine grade copper wires ordered. Relay ordered.

 

[g-man]

I have to say that my blower seems like its pushing more air and is more powerful since cleaning the switch contacts. I am tempted to plug back into the stock harness to see if the CB does not blow. After I replace the resistor I will amp and volt test the blower again. Then again after replacing grounds.

The way I understand current, once it flows through a motor, light bulb or whatever is expending the EDIT power , the polarity changes. So the red wire going into my blower from battery brings positive current and the short jumper wire coming out and going on to the resistor and switch is all negative current going to ground. It is a negatively switched circuit. The problem is what is causing too much resistance and raising the amps over the allotted 30. I still have to test the 10a a/c fuse coming off the fuse box. I assume it is no more than 10 amps but possible that the fuse is not that accurate and there are some draws on this side of the circuit.

Right now I have split into two circuits. One going from battery to toggle switch to blower then to resistor and selector switch to ground.

The other is the A/C fused side. This still gets it's power from the 30A heater CB then to relay then on to all the a/c stuff.

 

[g-man]

plugged the blower back into the stock wiring. Tripped the CB in about one minute. So cleaning the contacts on the switch didn't help with the CB.

Just pulled the blower relay and tested. I have no continuity between 1 and 3. It was pretty warm. I'll replace that next.

 

[g-man]

with the switch in Lo the only path for the blower to get power is to go through all three resistors in series

I don't agree with this. The contacts inside the switch each correspond to a diff wire coming in. I think the "LO" gets its current right from the blower relay. Look at the schematic again.

I think the 3rd coil inside the resistor takes any excess current to ground. Just a guess.

 

[OSS]

The only thing raising the current flowing through the circuit beyond spec is the (malfunctioning) fan motor.
Also there's no way to know if the 30 year old CB is really tripping at 30A or if its tripping lower.

Inadequate small gauge wiring is the norm for all the high current accessories on the cruiser. Toyota made a design compromise (with small gauge wires) to keep the wiring harness diameter manageable. If everything ran on 12awg wires, the harness would be as thick as your wrist.

Small wires, poor contacts and dirty slide switches will only increase resistance through the circuit which decreases amp draw.
The last time I measured amp draw through the blower motor on Hi, it was pulling 10A. Occasionally it would blow a 20 amp fuse (On initiall startup). Never blew a 30 A fuse.

I wouldn't recommend measuring voltage anywhere on the circuit while the fan motor is running. Any value you read is meaningless to us mere mortals. Voltage drop along different parts of the circuit is going to happen naturally when it is live.

There's an intermediate pigtail behind the dash (I recall) that connects the fan slider switch to the blower resistor. This pigtail has several slide pin contacts that plug into each other. If the contact is poor, resistance will go up (but not current) and the fan wouldn't spin quite as fast.

 

[g-man]

Ok so getting rid of weak ground wires and cleaning up my switch and replacing worn relays is just going to make my fan blow more. Get more volts to it.

My blower is only pulling 13.85 amps on high. Nowhere near 30a. The only thing that draws current that I have added is a new(er) compressor. I can test the amp draw on that but if it was over 10 amps the 10a a/c fuse would blow.

I did replace my 30 year old heater c/b with a new 30a one...still tripping.

 

[morganism]

Do a quick check for me, see if the coil is upping the amp draw. Just unbolt the coil cage bolts on the wheel well, clean em, and reinstall.
See if the CB trips right away again....

 

[g-man]

my clutch is drawing 2.8 amps.

rear heater switch is working and shows 0.00 amps when off. and 1.4 amps when turned on.

What else can draw amps?

Do a quick check for me, see if the coil is upping the amp draw. Just unbolt the coil cage bolts on the wheel well, clean em, and reinstall.
See if the CB trips right away again....

I just did this two weeks ago but I'll try it again.

 

[g-man]

I don't think the ignition coil is in the circuit tho.

 

[g-man]

in the schematic the idle up VSV has a squiggly line going through it like the magnet clutch. I'll check the amps on that but I can't imagine that being very much.

 

[morganism]

No, the bad coil ground will increase alternator output tho, check if the main wire off the alt is getting hot.

 

[g-man]

@morganism...

The ignition coil is not downstream from the 30a CB so no way can it be causing the breaker to trip.

@OSS....I appreciate your input but if the amps can't go up from worn grounds, worn switches, short circuits etc why are fuses and breakers measured in amps? Seems like if their is a short causing the fuse to blow or breaker to trip then that short has generated enough heat or whatever to cause the amps to rise above the rated level of the fuse/cb.

I am thinking about making 2 small jumpers and extending the 30a CB fuse out of the fuse box so I can get my ammeter around the wire. May be easier than pulling the fuse box out.

 

[g-man]

I don't agree with this. The contacts inside the switch each correspond to a diff wire coming in. I think the "LO" gets its current right from the blower relay. Look at the schematic again.

I think the 3rd coil inside the resistor takes any excess current to ground. Just a guess.

@Prairie Swamp ...having thought about this more I agree that the "LO" position DOES get it's power from the resistor as evident from me losing my "LO" speed after breaking the smallest of the coils inside the resistor. Since there are 4 wires going to the plug on the resistor and one is incoming from the blower, the other three must correspond to the coils and run to the switch. Which would mean the schematic is wrong.

I was wrong assuming that there was a ground going through the resistor or a separate wire going to ground coming of the resistor..as the schematic appears to show. Excess amperage is just consumed in the form of heat in the coil ..thus reducing the total amps in the circuit.

 

[OSS]

A short in a circuit upstream of a fuse or CB will increase the current (often catastrophically) where wires turn into heaters and crap starts melting and burning due to too much current flowing straight to ground (short). But anything in a normal circuit that increases resistance (degraded wires, poor connections) will decrease the overall current running through the circuit.

If there isn't a short somewhere but a 10A fan (on high) is trying try to pull 10A through a compromised connection in a plug, (which increases resistance) the plastic plug can overheat and start smoldering (smoking) leaving carbon crap deposits on the connector, increasing the resistance even more— making more heat and more smoke crap deposit until either the connector catches fire (rare) or it simply burns up to the point where no electricity will pass and he circuit is cut (when you're lucky).

The blower resistor is a good example of this. It's a mini toaster with resistance wire coiled up. It gets very hot due to the high resistance (to slow down the fan) which is why it's mounted in the flowing airstream in the duct.

 

[g-man]

I pulled the fuse box out and put my clamp on dc amp tester to the wire behind the 30a heater c/b. With the a/c on high and at park it was 14 amps. rev'd the motor to 2k plus rpms. It went as high as 16.4 amps. Drove around the street until the breaker tripped. It was only reading 14 amps when the breaker tripped. This is a new CB. Wires got warm. Found a small nick in the positive wire behind the CB. Probably from me probing it at some earlier time. No corrosion. No burned wires.

 

[OSS]

I wasn't aware that those circuit breakers were available any longer. Is it a "new" used one?

 

[g-man]

bought new when I got my a/c going and the first time the cb tripped. It was spring of 2016. Can't remember where I got it. Its a 8254 and not a 8286 so maybe a replacement for the outdated 82860-20011. Pretty sure it was new though. Looks the same. Of course as soon as that one tripped I started to figure out they can be reset so I went back and forth with the CBs. still have the original, both are tripping.

 

[g-man]

Assuming the CB are weak, how bout crimping some flat blade terminals on a 30a inline fuse holder, plug it into the c/b socket at the fuse box and see if the 30a fuse holds??