Voltage loss to blower motor (1969 with factory A/C)

[MaximRecoil]

I need to troubleshoot my blower motor. The problem is, though it has 3 distinct speeds (which means the resistor is working), they are all very slow. When it is on high, it is more like what I would expect low to be, and you can barely even hear/feel it on medium and low. This isn't a recent problem; it has always been like that ever since the first time I tried the heater in this car.

I connected the blower motor directly to the battery, and it worked good, at least twice the speed of its high setting when it's hooked up normally, and that's only with 12.6 volts (because the engine was off). So there has to be high resistance somewhere in its circuit, even on high when it should be bypassing the resistor.

The voltage at the fuse is good: with the engine running it is a little over 14 volts, and with the engine running and the blower motor on high it is a little under 14 volts.

So I'd like to check the connections at the resistor, but I don't know where it is, and I'd like to have an idea of where to look for it rather than just blindly tearing stuff apart hoping to come across it.

[A383Wing]

same place as a non-ac car...mounted in the front panel of heater box under dash....ye gonna have to take some ducting out to get to it

[MaximRecoil]

I don't know where it is on a non-A/C car either, but I know the heater boxes are different between an A/C and non-A/C car, so I mentioned it was an A/C car.

Is it located more toward the far right side of the car or more toward the transmission hump?

[Back N Black]

Here you go....

[elacruze]

The problem spots to look for are the firewall connector hot line and blower wire, and the keyswitch plug. Verify that they are not heat-damaged and use a vinegar/salt solution to clean the connectors (rinse with water, dry with hair dryer and reassemble with dielectric grease) The resistor terminals could be involved but seems unlikely since the problem is across all the commonly powered circuits.

[MaximRecoil]

Here you go....

Thanks for the picture.

The problem spots to look for are the firewall connector hot line and blower wire, and the keyswitch plug. Verify that they are not heat-damaged and use a vinegar/salt solution to clean the connectors (rinse with water, dry with hair dryer and reassemble with dielectric grease) The resistor terminals could be involved but seems unlikely since the problem is across all the commonly powered circuits.

The problem is quite the mystery to me right now, because while the relevant terminals may not be 100% sparkling clean, I can't imagine them introducing enough resistance to reduce the blower motor speed by at least half. As I mentioned in the OP, the voltage at the blower motor fuse is good (good at all the fuses for that matter), which comes after the bulkhead connector, so the voltage there is good by default too. That much resistance has to be generating heat somewhere, but I haven't found it.

[MaximRecoil]

Today I measured the voltage at the blower motor with the "heat" button pushed in and the fan switch on high (pushed all the way forward), and it is about 6 volts. Then something strange happened: I pushed the A/C button, and the blower motor increased in speed. I measured it and it was at about 9 volts, same deal with the Max A/C button.

What the hell?

When the fan switch is on high, shouldn't it be bypassing the resistor, and shouldn't "high" be "high" regardless of whether "heat" or "A/C" / "Max A/C" is selected? Where is the extra 3 volts coming from when I push the A/C or Max A/C button instead of the heat button, and why is it still a few volts lower than it should be? 

I still haven't found the resistor, but I haven't started removing duct work either (I don't look forward to doing that).

[ws23rt]

Today I measured the voltage at the blower motor with the "heat" button pushed in and the fan switch on high (pushed all the way forward), and it is about 6 volts. Then something strange happened: I pushed the A/C button, and the blower motor increased in speed. I measured it and it was at about 9 volts, same deal with the Max A/C button.

What the hell?

When the fan switch is on high, shouldn't it be bypassing the resistor, and shouldn't "high" be "high" regardless of whether "heat" or "A/C" / "Max A/C" is selected? Where is the extra 3 volts coming from when I push the A/C or Max A/C button instead of the heat button, and why is it still a few volts lower than it should be? 

I still haven't found the resistor, but I haven't started removing duct work either (I don't look forward to doing that).

Life is much better for us when you argue with yourself. 
Pretend that you are talking to a person and pick their answers to pieces. It is the same as eliminating possible causes for your problem on your own.
You can find the trouble and let us know what it was.   Much better

[A383Wing]

I don't care who ya are, that was funny right there.... 

[MaximRecoil]

Today I measured the voltage at the blower motor with the "heat" button pushed in and the fan switch on high (pushed all the way forward), and it is about 6 volts. Then something strange happened: I pushed the A/C button, and the blower motor increased in speed. I measured it and it was at about 9 volts, same deal with the Max A/C button.

What the hell?

When the fan switch is on high, shouldn't it be bypassing the resistor, and shouldn't "high" be "high" regardless of whether "heat" or "A/C" / "Max A/C" is selected? Where is the extra 3 volts coming from when I push the A/C or Max A/C button instead of the heat button, and why is it still a few volts lower than it should be? 

I still haven't found the resistor, but I haven't started removing duct work either (I don't look forward to doing that).

Life is much better for us when you argue with yourself. 
Pretend that you are talking to a person and pick their answers to pieces. It is the same as eliminating possible causes for your problem on your own.
You can find the trouble and let us know what it was.   Much better

Go hijack a different thread with your out-of-left-field inanities, simpleton.

[ws23rt]

Today I measured the voltage at the blower motor with the "heat" button pushed in and the fan switch on high (pushed all the way forward), and it is about 6 volts. Then something strange happened: I pushed the A/C button, and the blower motor increased in speed. I measured it and it was at about 9 volts, same deal with the Max A/C button.

What the hell?

When the fan switch is on high, shouldn't it be bypassing the resistor, and shouldn't "high" be "high" regardless of whether "heat" or "A/C" / "Max A/C" is selected? Where is the extra 3 volts coming from when I push the A/C or Max A/C button instead of the heat button, and why is it still a few volts lower than it should be?  

I still haven't found the resistor, but I haven't started removing duct work either (I don't look forward to doing that).

Life is much better for us when you argue with yourself.  
Pretend that you are talking to a person and pick their answers to pieces. It is the same as eliminating possible causes for your problem on your own.
You can find the trouble and let us know what it was.   Much better

Go hijack a different thread with your out-of-left-field inanities, simpleton.

No hijack-- I was answering to the topic and suggested a quick easy way to your needed solution.

We are here to help everyone and that is my motive.

BTW I am a simpleton in that I like things to get to the point. I say what I feel and the fewer words the better.  Communication is the bottom line however that happens.

A game of words leads off topic.

[MaximRecoil]

Again, since you don't read so well:

Go hijack a different thread with your out-of-left-field inanities, simpleton.

[ws23rt]

Again, since you don't read so well:

Go hijack a different thread with your out-of-left-field inanities, simpleton.

Is this a sttammer?

[MaximRecoil]

Again, since you don't read so well:

Go hijack a different thread with your out-of-left-field inanities, simpleton.

[ws23rt]

Just responding to a reply within a topic

[A383Wing]

Again, since you don't read so well:

Go hijack a different thread with your out-of-left-field inanities, simpleton.

Is this a sttammer?

his recording is stuck on repeat

[MaximRecoil]

Just responding to a reply within a topic

Again, since you don't read so well:

Go hijack a different thread with your out-of-left-field inanities, simpleton.

his recording is stuck on repeat

You should also go hijack a different thread, Ankle Biter #2.

[ws23rt]

Just responding to a reply within a topic

Again, since you don't read so well:

Go hijack a different thread with your out-of-left-field inanities, simpleton.

his recording is stuck on repeat

You should also go hijack a different thread, Ankle Biter #2.

When an ankle biter strikes and you feel the venom.  Where do you think that venom comes from?---
We are not naturally poisonous.  It is human nature to self defend.  You attack---we defend.  It will stop when the attack stops or we die.

Can this be a hijack?--- A response to the OP?

[ws23rt]

Today I measured the voltage at the blower motor with the "heat" button pushed in and the fan switch on high (pushed all the way forward), and it is about 6 volts. Then something strange happened: I pushed the A/C button, and the blower motor increased in speed. I measured it and it was at about 9 volts, same deal with the Max A/C button.

What the hell?

When the fan switch is on high, shouldn't it be bypassing the resistor, and shouldn't "high" be "high" regardless of whether "heat" or "A/C" / "Max A/C" is selected? Where is the extra 3 volts coming from when I push the A/C or Max A/C button instead of the heat button, and why is it still a few volts lower than it should be? 

I still haven't found the resistor, but I haven't started removing duct work either (I don't look forward to doing that).

Life is much better for us when you argue with yourself. 
Pretend that you are talking to a person and pick their answers to pieces. It is the same as eliminating possible causes for your problem on your own.
You can find the trouble and let us know what it was.   Much better

Go hijack a different thread with your out-of-left-field inanities, simpleton.

My understanding of what it means to hijack is to go off topic and start a different conversation.

I did not go off topic. I was on topic with my best advice to you to help you find the answer to your topic question.

You however asked--(told) me to go hijack a different thread--??? 

It seems to me as though you hijacked your own thread by changing the topic provoking a response to something that is off topic.

Don't you realize how rude it is to hijack??

Since you are the originator of the thread it may be just fine

Do you think this thread should be locked due to contamination??

[MaximRecoil]

When an ankle biter strikes and you feel the venom.  Where do you think that venom comes from?---
We are not naturally poisonous.  It is human nature to self defend.  You attack---we defend.  It will stop when the attack stops or we die.

"Venom"? What venom? Ankle biters have no venom:



And no, I don't "attack", and you won't find a single example of me doing so on this forum.

Can this be a hijack?--- A response to the OP?

Did your post point out the location of the blower motor resistor on a '69 with factory air conditioning, or did it contain possible causes of the low voltage to the blower motor? No, it didn't, and nothing else is relevant to my OP. Your post was nothing more than an irrelevant attempt at being a smartass, thus a thread hijack.

Ask yourself: would you have made the same post if the OP was my very first post on this forum? Obviously not. Your post was motivated by some pathetic little obsession you have with me personally (the same thing motivates all internet ankle biters), carried over from other threads. Replying to the poster rather than to the content of the post is always a hijack in threads of this type.

My understanding of what it means to hijack is to go off topic and start a different conversation.

I did not go off topic. I was on topic with my best advice to you to help you find the answer to your topic question.

You however asked--(told) me to go hijack a different thread--??? 

It seems to me as though you hijacked your own thread by changing the topic provoking a response to something that is off topic.

Don't you realize how rude it is to hijack??

Since you are the originator of the thread it may be just fine

Do you think this thread should be locked due to contamination??

See above, simple fellow.

[Cooter]

Fyi....these blower motors do not ever blow like newer cars. Chasing your tail on this one. If running Chrysler alt. Will run even slower when at idle.

[bill440rt]

The one in my '70 has the same characteristics as you describe. Not a powerful blow, but the A/C is still freezing.

Sorry to hijack.

[MaximRecoil]

Fyi....these blower motors do not ever blow like newer cars. Chasing your tail on this one. If running Chrysler alt. Will run even slower when at idle.

There still has to be a reason for it only being ~6 volts at the blower motor; that's a loss of over 8 volts compared to alternator voltage. Then the blower motor speed increases simply by selecting A/C or Max A/C, without touching the fan speed switch (measures ~9 volts at the blower then). But no setting on the controls gets it to the speed it is capable of when you connect it directly to the battery.

It must be going through one of the resistors in the blower motor resistor unit even when on high, and then going through a less resistive resistor in the same unit when A/C is selected. But that makes no sense; it should be bypassing the resistor completely on high; that's how it works in every vehicle I know of, and I believe the schematics in the FSM shows a resistor bypass circuit for "high" (I'd have to double-check that though).

The one in my '70 has the same characteristics as you describe. Not a powerful blow, but the A/C is still freezing.

Does your fan increase in speed simply by selecting A/C or Max A/C, without touching the fan speed switch? With the engine running, what is the voltage at your blower motor when "heat" and "high" are selected? What is the voltage at your blower motor when "A/C" or "Max A/C" and "high" are selected?

Sorry to hijack.

Say what?

[MaximRecoil]

it should be bypassing the resistor completely on high; that's how it works in every vehicle I know of, and I believe the schematics in the FSM shows a resistor bypass circuit for "high" (I'd have to double-check that though).

Okay, here it is:



On high, the blower motor resistor is bypassed; nothing but ordinary wires and terminals between the switch and the motor. So where am I losing ~8 volts on heat/high, and where am I regaining ~3 of those lost ~8 volts on AC/high?

[John_Kunkel]

I, too, was concerned about what I perceived as low blower speed (especially in HIGH) so I connected the motor directly to the battery and the speed rose to what I considered "correct"....problem is the motor got so hot it blistered the paint.

Draw your own conclusions.

[MaximRecoil]

I, too, was concerned about what I perceived as low blower speed (especially in HIGH) so I connected the motor directly to the battery and the speed rose to what I considered "correct"....problem is the motor got so hot it blistered the paint.

Draw your own conclusions.

That's interesting. Do you know what the voltage is at your blower motor when on "heat" and the fan is on high? And if you have A/C, what is the voltage when the fan is on high and "A/C" or "Max A/C" is selected?

I still can't imagine how the motor is being slowed down so much when on high. Though I haven't torn my ducting apart yet to look at my blower motor resistor and the wiring to it, the diagram from the FSM that I posted shows the resistor being bypassed when on high. Yes, there is a fairly long run of somewhat thin wire to it (probably 16 gauge), but that should only result in a drop of a volt or two compared to the alternator voltage, not 8 volts (or 5 volts when A/C or Max A/C is selected).

If I remember right, "Pete in NH" is an electrical engineer, so if he reads this, I have a couple of questions:

1. Based on that diagram, can you see anything that would result in an ~8.4 volt drop (from ~14.4 volts to ~6 volts), measured at the blower motor, with "heat" and "high" selected?

2. Can you see anything that would suddenly allow an extra ~3 volts (from ~6 volts to ~9 volts) to make it to the blower motor, thus significantly increasing its speed, when "heat" is deselected and "A/C" or "Max A/C" is selected (fan speed switch not touched, i.e., still on "high")?

[Pete in NH]

Hi,
I have the same diagram Maxim posted in a 69 Plymouth FSM I have. What they are not showing us are the switching functions in either the blower speed switch or A/C controls, so the following are just some educated guesses. Note they are showing three resistors in the blower speed control set up, if you were bypassing all resistors in the high speed setting you would only need two resistors. So, I suspect they are leaving one resistor in the circuit even on high speed. The way the circuit diagram is drawn and without really knowing the switch internal functions I'm guessing at the following- warm heater air is lighter and easier to move than cold A/C air so for the A/C mode they bump up the motor speed even more over the high speed heater position.  I think there is always a resistor in the circuit because as John mentioned the motor is likely something less than a true 12 volt motor. I think in the heater high speed position you have a resistor of a certain value that winds up with another resistor in parallel with it in the high speed A/C position to lower its value a little more. I suspect you could confirm all this by tracing the switch functions through the switches and then drawing the whole thing out.

[MaximRecoil]

Excellent. Your explanation makes sense, thanks. I guess I can leave the blower motor alone, and that's one less part of the HVAC system I have to worry about fixing.

Now I only need to replace the torn flexible ducting that goes to the defrost vents on top of the dash, and do something about the leaky temperature control valve on the firewall (I currently have it bypassed so it is always on hot). The former will be easy; the latter won't.