Blower/fan question deux - only on high, now stops working

[HeadlessHorseman]

Originally Posted by inqzitr

There are times that I stop the car, and the fan continues blowing, even though everything is off.

Your Blower Motor Relay is probably frozen in the closed position - replace the Blower Motor Relay (about $8-$12) and your problem will disappear.

Originally Posted by inqzitr

There are times that I turn on the fan (i.e. from off to 'high'), and it wouldn't start. However, in about 3-5 sec. it would.

Again, most likely, your Blower Motor Relay needs to be replaced - it could also be your Blower Motor's worn brushes. It could also be burned or pitted relay contacts that fail to convey your instruction to START. Replace the Blower Motor Relay FIRST and see if this fixes all of your problems (it might). Check my post "1996 Dodge Grand Caravan... 101" It's all there. Though the locations of certain devices are different, the concepts are exactly the same...

http://www.automotiveforums.com/vbul...d.php?t=340871

[clhall]

Dodge Grand Caravan, 2001. As with many others here, my fan works on high only. This problem occurred the first time about 1 year ago. I replaced the BMR, which is located directly behind the glove box. This fixed the problem. However, about 2 months ago, the problem reoccurred. I replaced the BMR again and it fixed it again. However, the problem reoccurred last week.

Anyone know why this is reoccurring?

Thanks.

[HeadlessHorseman]

Originally Posted by mvollmar11

In case I find this is also the problem with my 96 did they tell you where the relay is?

Every thing you need to know...

http://www.automotiveforums.com/vbul...d.php?t=340871

[clhall]

If this is in response to my question, that info does not address my particular situation of repeated resisters going bad.

Thanks tho

[HeadlessHorseman]

Originally Posted by clhall

If this is in response to my question, that info does not address my particular situation of repeated resisters going bad. Thanks tho

As noted in my response, my reply was to mvollmar11, who was trying to locate the Blower Motor Relay in a '96.

There are other people on this board who are experiencing the very same recurring Resistor Block failure you describe. Unfortunately, they too are at a loss to determine exactly why this is happening. Let's think through how the AC/Heater Switch, AC/Heater Blower Motor Relay, the Resistor Block and the AC/Heater Blower Motor electrically work together.

As I understand it, the Blower Motor Relay is hot at all times and actuated by the AC/Heater Switch (in the ON position) to provide a constant supply of power (+) to the Blower Motor via its Dark-Blue wire. The AC/Heater Control Module provides the ground plane path to the AC/Heater Switch which in turn directs the Blower Motor to this path through the Resistor Block to spin the motor.

Depending on the slower AC/Heater Switch setting (Lo, M1, M2, M3), DC current (power) is drawn through a particular Resistor Block coil where the current is reduced to spin the Blower Motor at a slower speed (None for the "Hi" setting). The more a Resistor Block coil "resists" the DC current at a particular setting, the slower the Blower Motor spins.

In other words, the Resistor Block functions to deprive the Blower Motor of electricity at four different levels to provide four different speeds... all less than the "Hi" setting... that's why there are four coils on the Resistor Block. In the AC/Heater Switches "Hi" setting, none of the Resistor Block coils are used to provide the fastest speed possible for the Blower Motor.

Are you still with me so far ? Hang in there... I'm still thinking this through, "out loud."

We know that the main byproduct of electrical resistance is HEAT. This heat is generated by the Resistor Block's coils - MORE heat is produced by the coil that provides current for the slowest speed (Lo - more resistance), LESS heat by coils that provide power for middle speeds (M1, M2 & M3 - less resistance) and NO heat for the fastest speed (Hi - no coil/no resistance).

The question seems to be, why do these coils burn out so quickly?

Maybe the BETTER question is, why do these coils get TOO hot?

We should reasonably suspect that the hotter these coils get, the more likely it is they will burn out. I think this also means that the more POWER going through these coils, the more likely they will get HOTTER, maybe TOO hot, possibly more heat than the Resistor Block was designed to handle. Why else would some owners report melted sockets and plugs?

We know the only thing drawing power through the Resistor Block is the AC/Heater Blower Motor. Since the Blower Motor circuit is protected with a 40AMP fuse, we also know that no more than 40AMPs will ever be drawn through this circuit.

Given all of this, we might draw two conclusions...

1.) The Resistor Block (and socket/plug) is under-engineered to handle up to a 40AMP load, AND

2.) The Blower Motor is consuming more power than the Resistor Block can handle, even though BOTH devices are operating within the 40AMP maximum circuit limitation.

If I am correct in these conclusions (hopefully I am... and I invite anyone to jump onto this thread to discuss it), I see two possible solutions to this problem...

1.) Replace the Blower Motor and hope it actually consumes less power than the one it replaces, and/or

2.) Attenuate (reduce) the (+) DC power through the feed (Dark Blue wire) to the Blower Motor to consume less DC power and thereby generate less heat in the Resistor Block which is causing it to fail. A heavy-duty Varistor (variable resistor) might get the job done, though I have not looked into this as a possible retro-engineering solution. One downside I see for sure in reducing the power-draw with a Varistor through the Resistor Block to the Blower Motor... this will also reduce the speed of the Blower Motor in ALL speeds, including "Hi."

Bear in mind, I may be talking out of my butt here. Still, replacing the Blower Motor is probably the best first step to take because it is the motor itself that draws the power that is likely burning out the Resistor Block. It might be that the motor currently installed is old or maybe it's slightly different than the original/OEM motor (if it's already been replaced), drawing slightly more power, but enough "more power" to raise hell with the Resistor Block.

In the end, this is just a guess... Please report back to this thread if/when you resolve your issue. Although I am not experiencing this problem in my '96 GC, there are other owners who are! In any event, Good Luck & Happy Hunting!

[dougpeng]

My 1999 Voyager lower fan settings stopped working too (leaving only the highest and second highest settings working), and I took your advice and replaced the Blower Motor Resistor under the front hood on the passenger side firewall. It was a 10 minute job and now all my fan settings works! Thanks for the advice! I took the liberty to write instructions on how to replace this Blower Motor Resistor WITH PICTURES for others to follow. Please see my website http://www.execulink.com/~scitech/BMR/Index.htm on the full instruction. - Doug Peng [email protected] Toronto, Canada

[bolognaman]

I really appreciate all of the information in this post, it was helpful. BUT...I still have some issues. My blower works in the off and high positions only, nothing in between. I have installed a new resistor (not a 10 minute job in my van, more of a PITA). Anywho, I have pulled out the tester and I do have voltage coming to the resistor for each setting (lo, med 1, med 2) and that the new resistor does pass a current through it. All contacts are clean. I have poured over the wiring diagram and feel that I am at a dead end. I can't find any other path for the circuit. Any thoughts from anyone on how to regain my lower speeds? Thanks.

[dougpeng]

Originally Posted by bolognaman

I really appreciate all of the information in this post, it was helpful. BUT...I still have some issues. My blower works in the off and high positions only, nothing in between. I have installed a new resistor (not a 10 minute job in my van, more of a PITA). Anywho, I have pulled out the tester and I do have voltage coming to the resistor for each setting (lo, med 1, med 2) and that the new resistor does pass a current through it. All contacts are clean. I have poured over the wiring diagram and feel that I am at a dead end. I can't find any other path for the circuit. Any thoughts from anyone on how to regain my lower speeds? Thanks.

Gee, your problem seems severe and I am at lost to suggest something useful. however, I also pulled out the HVAC unit from the central front dash and examined the fan switch. I must say that it is pretty robust design and I doubt it would be your problem, but you could try. The entire HVAC unit has PCB on it that looks pretty sophisticated, but the fan switch doesn't look like it is part of it (assuming you have the standard manual fan and not the climate control system) - Doug Peng