So I think I lost a bet...

[Wildchild467]

74M35A2 was changing batteries in his M925A2 last night and there is a wire that goes to the 12 volt side of the batteries with the wire number 569. He bet me lunch that the 569 wire powered the low speed of the heater blower motor. Well sure enough he flipped the battery switch and the blower turned on low speed. I thought it's bad to pull power from one battery like that. I know the 809 series did it for a grid heater for cold start though. Anyway, back to the 939 series... does that wire power the low speed of the fan and the blower motor does not have a resistor? What gives? I'm all for buying the man lunch but I don't under stand what the 12 volt wire does on the 939.

 

[davo727]

The abs is powered by a 12 volt tap off one battery on the 939A2.

 

[74M35A2]

Maybe on ABS, but for sure blower low speed also. You proved it yourself, and now I am going to make you eat lunch with chopsticks.

 

[lindsey97]

 

[dawico]

My understanding is the blower motor is on low with 12 volts and high with 24 volts. I am not positive which wire it is though.

The blower motor doesn't pull enough power to adversely affect the batteries with a 12 volt draw. Add 15 other units that pull off one battery and then the trouble begins.

That is my understanding of the situation anyways.

 

[wheelspinner]

If I am not mistaken, the 12v is used as "opposing" voltage. So the motor slows down because it can only use half of the 24V. It happens inside the motor. Its basically using the 12V as a resistor. So you both kind of won, and its a draw.

 

[doghead]

Grasshopper, the answer can be found in the Tm, but the understanding must transpire in your head...

"When you can snatch the pebble from my hand, it will be time for you to leave.".

 

[hklvette]

Grasshopper, the answer can be found in the Tm, but the understanding must transpire in your head...

"When you can snatch the pebble from my hand, it will be time for you to leave.".

or in P2P...

 

[74M35A2]

The abs is powered by a 12 volt tap off one battery on the 939A2.

I don't believe this to be true. My ABS light runs the normal self-test diagnostics at ignition on, and I just activated the ABS on the icy road to my house, and saw the rear wheels pulsing while the fronts were locked up. The ABS light and system is functioning correctly with the 12V wire off inside the battery box.

A review of the wiring diagram would confirm, which I have not done, but I still believe the 12V tap wire in the battery box of my M925A2 powers the low side of the heater blower motor only.

 

[74M35A2]

If I am not mistaken, the 12v is used as "opposing" voltage. So the motor slows down because it can only use half of the 24V. It happens inside the motor. Its basically using the 12V as a resistor. So you both kind of won, and its a draw.

? It is DC current, so the only way that could work is if it offset the ground plane of the entire vehicle, which it does not. It is simply routed to the low side of the blower motor switch. Not difficult, and Tom owes lunch, because he said my truck uses a blower motor resistor like his M35A2 used to (I suggested to him that he just use 12V to the low side of his switch when his resistor toasted. He was worried about finding an improved or higher wattage rated resistor, and I said to just source 12V from his battery bank, without knowing that is how they later did it on the M939 series.).

And that, my friends, is a free lunch!

 

[74M35A2]

The abs is powered by a 12 volt tap off one battery on the 939A2.

Where is this info coming from? My ABS is working perfectly with the 12V tap wire off, confirmed by testing and ABS self test light. The only thing not working is the blower motor on lo speed. It is working correctly on hi with this wire off. With the blower switched on Lo, and touch this 12V tap wire to the 12v battery post, it sparks and the fan comes on. With the blower on hi or off, and I touch this wire to the 12v battery post, no sparks (current), and no other detectable changes on the vehicle systems.

At this point, even if it is listed as powering the ABS system in the diagram or P2P, I call BS because my ABS is working as we'll with it off, but the blower Lo setting is not.

 

[gem1410]

the 12 volt battery tap wire goes to the battery switch first--when the battery switch is turned to on position the 12 volts goes by wire to the blower control switch--when the blower switch is turned to low the 12 volts goes to the blower motor------that is all that wire does--except in my M923a2--in my truck the wires at the battery on off switch were crossed so the blower was getting 24 volts on hi and low sides and the pcb box on the fire wall was getting 12 volts--the pcb gets power from the same switch dpdt-my truck would not always get power anywhere--the truck had a new pcb on it-------------took some deep thinking to figure it out--changed the battery on off switch wires around to correct positions and truck gets 24 volts to box and works-----heater now gets 12 volts on low side----took 2 weeks of thinking and then 2 minutes of playing with the p2p software

 

[Suprman]

None of my trucks blower motor work on low only high. I have the 12v tap on my batteries I though it was abs. There is an extra wire with a packard connector up by the blower motor zip tied. I had though that was for the low fan speed if you had a fan capable of it.

 

[gem1410]

most of mine work on low and high--do a voltage check on the blower switch--one side is 12v other is 24v--only works with battery switch on

 

[Wildchild467]

Grasshopper, the answer can be found in the Tm, but the understanding must transpire in your head...

"When you can snatch the pebble from my hand, it will be time for you to leave.".

You are absolutely right. I was just in shoak because I thought I had this one in the bag. I thought people would like to hear how I lost the bet. Haha. I know the 809 series used it for the grid heater I believe. I will research it to make sure I lost the bet.... even though I think I did. It's all fun and games

 

[74M35A2]

None of my trucks blower motor work on low only high. I have the 12v tap on my batteries I though it was abs. There is an extra wire with a packard connector up by the blower motor zip tied. I had though that was for the low fan speed if you had a fan capable of it.

Fan motor is just 2 wires, like mentioned above, that 12V wire goes from the battery, to the ig/batt switch, to the blower switch, to the blower motor.

Hey, you could use one of your 12V batt equalizers to get your low speed blower fan working! Just kidding bud.

 

[74M35A2]

You are absolutely right. I was just in shoak because I thought I had this one in the bag. I thought people would like to hear how I lost the bet. Haha. I know the 809 series used it for the grid heater I believe. I will research it to make sure I lost the bet.... even though I think I did. It's all fun and games

You'll also be in "shock" when you get the lunch bill. Don't forget to tip!

 

[tbar123]

The wiring schematic is in Appendix H of TM9-2320-272-24-4. I just had to run down the same wiring myself since my motor fried. I know it was seized, because I had to use a large screwdriver to free the fan. I do know that the low side is 12v and the high 24v.Looking at the schematic, 1 wire in from the battery switch( which comes from the protective control box),1 wire out to the heater, 1 wire that seems to end up at the diagnostic center. Atleast that's the way it seems on my A1.

 

[74M35A2]

You are absolutely right. I was just in shoak because I thought I had this one in the bag. I thought people would like to hear how I lost the bet. Haha. I know the 809 series used it for the grid heater I believe. I will research it to make sure I lost the bet.... even though I think I did. It's all fun and games

Shoak: To let out a mild grunt while being penetrated.

http://www.urbandictionary.com/define.php?term=shoak

 

[tbar123]

Coke bottle!!!