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  #1  
Old 10-17-2019, 08:53 PM
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To rig or not to rig climate blower motor

My 84SD's climate motor quit blowing. It seems like the push button controls the temp ok. Both Fuse 10 and 11 have power. and the blower works when given current and ground directly from the battery but not via the push buttons. I'm thinking of plugging in to the connection for the cigarette lighter and using that with a rheostat to power fan motor.


I have a parts car to scalp some connectors and wouldn't have to cut into the harness of the driving car. How much load would the blower would add to the lighter circuit?



Are any of these easily delivered switches appropriate?


https://www.amazon.com/s?k=12+volt+rheostat+variable+speed+control&crid=127K5JIE2UACG&sprefix=12+volt+rheo%2Caps%2C164&ref=nb_sb_ss_i_1_12


Thoughts on any other way to solve the problem? I think because the temp indicator tape looks new this unit is one that member James Dean worked on but am not sure. My objective is to quickly have working heat that the wife could work until I get around to actually finding the problem.
Other projects are lined up in front.

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Old 10-17-2019, 09:31 PM
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Probably a bad silver box. It's the "brain" behind the whole system. The capacitors leak and eat the traces off the circuit board, then it does random crap or just quits altogether.
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  #3  
Old 10-17-2019, 10:55 PM
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Quote:
Originally Posted by Diseasel300 View Post
Probably a bad silver box. It's the "brain" behind the whole system. The capacitors leak and eat the traces off the circuit board, then it does random crap or just quits altogether.

So, what about an answer to the rig above. I need heat and would prefer not to spend time getting educated on whatever minutia is necessary to bring the system up to specs.
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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. Probably up for sale in the fall 2020 still have it. 85TD beginning to repair to DD status. Waiting on shop to do minor but more than I can do rust.
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  #4  
Old 10-17-2019, 11:04 PM
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To rig or not to rig climate blower motor

AlI I saw were 10 amp on that page.


RioRand 7-80V PWM DC Motor Speed Controller Switch 30A https://www.amazon.com/dp/B071NQ5G71/ref=cm_sw_r_cp_tai_q9rQDbK9VGBQN
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  #5  
Old 10-17-2019, 11:14 PM
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Blower motor draws too much current for the cigarette lighter wiring I suspect. I might feed wires from the resistance coils to various toggle switches for fan speeds.


I do not have a schematic. Although it does not matter if those coils are on the power side of the motor or not. They can be in the ground leg as well. All wire and parts you add have to withstand 30 amps I believe. Others will correct any errors I make. I use and like an all metal toggle switch I buy direct from China. At somewhere around two dollars each delivered from China. for many applications. They are always on Ebay.

I might be concerned about motor heating with the device you propose. Just not familiar with pulse fed dc brushed motors. Other members may be.

Last edited by barry12345; 10-17-2019 at 11:33 PM.
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  #6  
Old 10-18-2019, 06:08 PM
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Check Fuse F11, it's 25Amp and that's about all it powers is the blower motor controller and blower motor.
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  #7  
Old 10-18-2019, 07:43 PM
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Fuse 11 powers the fan only when the switch is working and turned on. I took the switch off the push button unit and have no continuity between any of the 4 contacts. I don't know which contacts are supposed to have continuity under what combination of button pushes but there was 0 continuity under all arrangements.
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  #8  
Old 10-19-2019, 12:49 AM
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switching to a different circuit is not as good an idea as debugging the existing circuit. is there potential at fuse #11? for a four position switch (SP3T+off), there should be only one continuous pair of contacts for each of the three speeds.
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  #9  
Old 10-20-2019, 01:42 AM
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Does he need to go through any resistance coils if he just wants the motor to have a single speed at the max speed?

If he does not need the resistance coils and wants it to go at max speed he could wire it up like a electric coolant fan but with out the fan controller.

you find a source that is hot when the ignition switch is on and run that to operate the a relay and that is not the high current part of it. Then you wire the fan + with an inline fuse to the relay and from the relay to the fan to ground. The relays can take various amperages so you have to get one that is of a higher amperage the what you need what you need.

In place of the Fan controller/temp sensor you would put an on and off switch.

Of course the blower control on off would be entirely separate from the stock one.

To see some diagrams of that do a goole image search and look for fan relay or electric coolant fan diagrams and so on.

In the diagram terminal 86 would have the on off switch and the current from the Ignition switch source. Terminal 85 goes to ground. And that is the circuit that turns the relay on and off. Depending on what source you use when the ignition is on there may already be a fuse in the circuit.

Terminal 30 has the + high amperage source and could have the fuse in the circuit and terminal 87 is the + high amperage gong to the Blower Motor and the motor itself would have a separate ground.

I don't know a lot about this but I managed to install an electric coolant fan once with a similar relay except that the on off switch is the Fan Controller/Temp Sensor.
When I was looking the relays up they are often referred to as Bosch Relays even though they were not made by Bosch. My van Chevy uses 4 the same relays with variously amperages for different functions so they are common (one of them I remember is the electric fuel pump).
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Last edited by Diesel911; 10-20-2019 at 02:08 AM.
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  #10  
Old 11-07-2019, 06:06 PM
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How is the fan speed controlled in the stock system? If it's voltage, wouldn't a fused switch to a relay to a rheostat that controls fan speed work?

I've been wanting to add some circuits and thought about putting the controls in the console below the center arm rest. There'd be room for switches if I made a wood panel that fits into the console. This wouldn't require any hacking of the wiring or console unless I want something tied to the ignition switch. It could easily be put back to stock.

It seems like a fused relay hot only with the key at run position could be used to power the added circuits. There is room to add a fuse box to the passenger side of the engine compartment.
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  #11  
Old 11-07-2019, 09:06 PM
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The fan speed is controlled by the black box next to the silver box. I’m going through my system now on my 85 300d. The black box has a bunch of relays that switch the power resistor coils on the firewall in and out of the circuit.

My blower only doesn’t work on EC. On Min AC it works fine. I totally rebuilt the silver box. Found some weak capacitors and a burned Darlington transistor. Replaced the two op amp chips too for good measure. Still no love from the blower on EC. Posts seem to say this symptom is pushbutton problems. I tried resoldering the PBU boards and it didn’t help. With the new capacitors and transistors it now has a totally new set of bugs. It opens the monovalve and won’t shut it.

Enough of my issues.

Yeah, a relay to the blower will Jerry rig it. You can also put a ball valve in place of the heater aux pump to modulate heat with a cable control. I’ve seen images on Google where people make their own home brew controls for all the flaps and hot water using cables and toggle switches. I’m so frustrated I’m almost there.

I bought a programa PBU last night as a last ditch effort.

The fused relay and rheostat will work but you’ll need a big one to handle the fan current. Not some little audio thing. Take a look at the fan speed resistor on the firewall, your rheostat will have to run as hot as those to slow the fan. Realistically I’d use a bunch of toggle switches to switch the existing resistors in and out of the circuit. That is what the black box does with some relays.
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  #12  
Old 11-07-2019, 09:15 PM
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Many of our W123 cars are equipped with an auxiliary water pump which helps to circulate coolant through the heater core. If the auxiliary pump goes out it can take the PBU with it. It is recommended to install an inline 3 amp fuse in the wire going to the auxiliary pump.
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  #13  
Old 11-07-2019, 11:19 PM
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The temperature seems to be working fine with the rotary. My final question to clarify is "can I use a rheostat to control fan speed"?

My understanding is the rheostat will vary the voltage to the fan. I think (understand/believe perhaps incorrectly) that some fans are built to only run correctly long term with current to one of several available terminals and not with varied voltage to one terminal.
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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. Probably up for sale in the fall 2020 still have it. 85TD beginning to repair to DD status. Waiting on shop to do minor but more than I can do rust.
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  #14  
Old 11-08-2019, 01:30 PM
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The motors that use different windings for different speeds will have more than two wires connecting to them. . Or that is how I would identify them. Also they would have no resistance coils in them.
so obviously you do not have a tapped type winding motor of some form. A rheostat will work but it has to handle 25 amps of current. That is a substantial rheostat I suspect. I did not bother to look up or price one.

You start changing direct current to some form of chopped up waveform with an electronic controller may be hard on the motor brushes and could cause motor heating. May not yet could.
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  #15  
Old 11-09-2019, 12:27 AM
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You bet. Look at the big coils in the heater resistor. Your rheostat will have to have coils like that. In theory, you can use a switched power scheme using pulse width modulation of a MOSFET switch with a low on resistance. But seriously, just rig some switches to the existing fan resistor. Forget about the rheostat.

Edit - oops sorry. Just checked your link for your Rheostat. What you have there is a micro controller based pulse width modulation system with a MOSFET stuck to a heat sink. This will work if you get one that can handle the current going to the motor. I recall its around 10A.

Sorry I didn’t check your link. I do think something like this will work.

Update - aww man. Put in a new pushbutton unit on the 300d. It is better. It doesn’t just blast hot air for no reason. Fan still doesn’t turn on on EC unless I push on AC or defrost buttons first.

Good luck with your fan. I need to trace the fan circuit on EC. On my 300sd the blower always turns on when the fan button is on and the system is on AC. Maybe I’ll jerry rig mine with a switch to the fan resistor.

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82 240D stick shift 335k miles (SOLD)
82 300SD 250k miles
85 300D Turbodiesel 165k miles

Last edited by ykobayashi; 11-10-2019 at 01:29 PM.
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