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I have this 07 Grand Caravan SXT with a 3.8L engine. Initially it came in with the blower motor not working. We diagnosed it, replaced both the blower motor resistor and the blower motor. Since that time (3 month) we have had 3 more blower motor resistors fail on high speed. My question is "In attempting to diagnose this failure pattern, what am I looking for"? If I check on the battery feed wire to the blower motor, there is battery voltage there and voltages of varying voltage as the blower motor switch is rotated to the slower speeds. By all indications this is within parameters. Obviously I'm missing something. But what?

Voltage is not as important as amperage. Measure the amperage on high. I suspect it will be high.

Regarding the blower and resistors, were they OE?

ricmorin wrote:Voltage is not as important as amperage. Measure the amperage on high. I suspect it will be high.

Regarding the blower and resistors, were they OE?

Bingo.

I agree: amperage is the critical measurement. What amperage draw should I see with the blower motor switch set to high?

No, I did not use OEM parts. Is that where I made a mistake? I used a Standard resistor and a 4 Seasons motor.

Additionally, since you called this a blower resistor I am assuming this is a manual AC system and not automatic. The automatic system uses a blower module, not a resistor. Am I correct?

ricmorin wrote:Additionally, since you called this a blower resistor I am assuming this is a manual AC system and not automatic. The automatic system uses a blower module, not a resistor. Am I correct?

Correct. The automatic system uses a blower module, not a resistor as such. However, in this case, we have a manual HVAC system.

Awesome. Sounds like the thermal fuse is blowing in the resistor. I suppose a poor connection at terminal 2 could create additional heat that is being transferred to the resistor, but I'd still like to see that amperage reading.

Does the driver use high a lot?

Just a thought, is the harness ok. We replace a bunch of them.

Rich wrote:Just a thought, is the harness ok. We replace a bunch of them.

In closely examining the wiring harness connecting to all 6 terminals of the resistor, there is no evidence of overheating. There is even the marks made by the female terminals on the male terminals so I am forced to assume that there is a solid connection. Would you still advise harness replacement?

Tim Martin wrote:I agree: amperage is the critical measurement. What amperage draw should I see with the blower motor switch set to high?

No, I did not use OEM parts. Is that where I made a mistake? I used a Standard resistor and a 4 Seasons motor.

It varies from make to make. The rule of thumb is the fuse should be 125% the load. I personally like to see the amperage at 50% the rating. It could be even lower. A quick check of a known good would help.

For older vehicles, aftermarket is usually fine here. But sometimes you get a bad one.

So, the amperage draw of 13 amps with the speed selector on the fourth setting is high. So, apparantly even with a new motor, it is drawing too much. Cause if the fourth speed is drawing 13 amps, high speed will draw more and we have a 40 amp dedicated fuse for the blower motor so using your theory Ric, I could be seeing easily well over 20 amps at high speed, right? I do not have a new resistor here yet but I will test the amperage draw on high as soon as it comes and post the result.

Check it with another resistor. 20 or more sounds high to me. Try getting a known good sample.

Ok. Im back. Installing a new OEM resistor has given me a high speed blower motor draw initially of 28 amps, after a few seconds of running it drops back to 23 but varies from 22-25 while running. At the same time, I am hearing the blower motor changing speed as well as sound. Like up and down in rpm. Im thinking that I have a faulty blower motor which is blowing out the main resistor due.

Ok, I just connected a new blower motor to the resistor and ran it. The new one has a draw of only 19 amps and it is rock steady. I think I may have found the problem.

It is kind of frustrating that I cant seem to find OEM specs for this vehicle as to what blower motor amp draw should be.

Agreed.

Ric, would you say that the blower motor draw amperage specs I am seeing are pretty much applicable to most vehicles?

Im trying to get a better baseline for diagnostic purposes because we do alot of this kind of work and we do see many Chrysler Products blower motor failures. Perhaps more than any other brand.

The motors that I have checked are usually in the 15 to 18 amp area. Some even around 12-13.

ricmorin wrote:The motors that I have checked are usually in the 15 to 18 amp area. Some even around 12-13.

Thanks for your help Ric. I greatly appreciate your input on this particular application as well as general diagnosis on other vehicles.

You're welcome. I always did love a good mystery; part of why I love what I do.

I'm getting sick and tired of mysteries. However why I'm doing what I do is a mystery in itself. As far as the aftermarket issue goes I'm finding more and more parts that are showing signs of installation or tag overs. In the past year I've been noticing a lot of re-boxed parts. They've always been around but seem to have exploded. I'll purchase a part from a specific manufacturer that I've had great experience with and is a proven quality part, new, never reman and would fit like I expected. My techs are getting exasperated and I'm loosing money when we open a box to find the part used, a core, universal, or a piece of crap. On top of all this there isn't another one local through any part supplier and the vehicle is tying up a service bay or is blocking the shops main entrance. I'll not get into the rest of the negative points because I don't want to start festering over this. It's getting pretty bad when new parts need to be tested more than the one they have been purchased to replace. I really need to quit now because I am beginning to dredge up a few of the most recent failed new part syndromes. I needed to laugh sine crying hurts so much.