[Igor V. Nechaev]

When my resistor block went out I just cleaned it thoroughly and put some grease on contacts. Three years since then - no problem.

But on '01 they changed the design and loaction of the block, IIRC.
I've been told that there is some sort of thermal fuse in it, which goes bad now and then.

[Rick Anderson]

You've saved me starting a new thread. I just replaced the resistor block in my '02 Grand Caravan less than a month ago, it went out during a sever cold snap. Well we just had another cold snap and the brand new one went out again.

I'm suspecting the temperature is a contributing factor, I've never had a blower motor go bad, no does my motor show any sign of problems, other than the blowing resistor block at extremely cold temps.

Is there a test to confirm the motors condition? It works fine at high, like it always had before. Is there a resistance value for the motor?

I'm conteplating just soldering a shorting wire over the thermal fuse in the resistor block, cause I tested the old unit I pulled and the only thing that was wrong was the little fuse in the block was open circuit. I don't know if its a thermal fuse, it must be, since why else would there be a fuse in there for a circuit already protected by a replaceable fuse.

[Rick Anderson]

Another thing to consider? I replaced my thermostat before last winter, as a preventative measure. The dealer item was way to expensive, I bought an aftermarket NAPA model. Sometimes the OEM are funny temps like 192°F while the aftermarket are rounded off to a more universal figure like 195°F.

Now, if on a cold day, your in recirc and pumping as much heat as possible, can an extra 3° or so of the heater core make enough of a difference to blow the thermal fuse in the resistor block?

GrandCaraVan01, have you replaced your thermostat as well?

We can't rule out a bad thermostat as well, I've seen thermostats less than a year old go bad with huge temperature swings during the season changes. The heater core running a little hotter, not enough to notice on the UNGRADUATED temp gauge, but enough to blow the fuse?

[Rick Anderson]

This is from a prevous post of mine, when I first replaced the Resistor Block.

Quote

The old Resistor block looked perectly fine, I even checked the continuity and resistance on all the elements, which seemed fine, less then 10 ohms with a difference of a couple of ohms between each. But there is a cylindical electronic component leading to one of the motor tabs. This did not pass countinuity with infinite resistance. Perhaps its a diode or capacitor that I was testing wrong with my multi-meter. The new Resistor block, that electronic cylindrical piece, you can read the writing on the side, its 250V, 30A, 144°, looks like its a fuse to me, it must have blown on the old resistor block.

I'm going to look for a thermal resistor of the same spec and try to replace just the thermal resistor, it has to be cheaper than the $30 for the whole resistor block which is probably just fine like my original resistor block.

Radio Shack has thermal resistors, and they look just like the device that blew in the resistor block, unfortunately they are not of the same spec as the one I need, I may have to mail order it.

One more contributing factor to consider. Interior Air Filter, the 4th Gen Vans have an air filter that filters air just before the blower motor. If that filter is clogged, it would decrease air flow thru the system and over the resistor block, this could raise the air temp and maybe blow the fuse.

I replaced my filter at the same time as the thermostat, more than a year ago, it was aftermarket as well, perhaps its clogged. I'll be pulling it tonight and inspecting it.

[Beans]

Just a few weeks ago, someone posted that they found that exact fuse (same mfg — same part#) at Radio Shack for a couple bucks.
You might be able to find that post if you type the numbers on that fuse into the search engine. I think I remember the poster mentioning the numbers on the fuse.

This post has been edited by Beans: 28 December 2005 - 12:29 AM

[Rick Anderson]

Beans, on Dec 28 2005, 05:27 AM, said:

Just a few weeks ago, someone posted that they found that exact fuse (same mfg — same part#) at Radio Shack for a couple bucks.
You might be able to find that post if you type the numbers on that fuse into the search engine. I think I remember the poster mentioning the numbers on the fuse.

Umm, yea, my post from last month. I must have read the thermal fuse wrong.

I just took the new (and blown) resistor block out of the car, the thermal fuse specs are:

144°C, 250V, 10A

That is the exact thermal fuse they sell at radio shack for $1.49. Well, except I think the radio shack version is 240V, which shouldn't make any difference. I even picked it up, to have on hand, just in case I wanted to try it.

But dummy me, I didn't pull the new resistor block first, I grabbed the old one still laying around. Since I thought it need a 30amp thermal fuse that I can't find, I left the 10 amp thermal fuse on the desk and took a regular 30amp fuse and soldered it over the blown thermal fuse to short it, but still supply some circuit protection. Put it in, works great again. Of course I look over the new resistor block I pulled and discover it has a 10 amp thermal fuse, so I could have used the radio shack version, I'll probably pop it in tomorrow night and give it a try.

The fuse block/PDC does NOT have a blower fuse, just a rear blower fuse, with relays for both so I'm assuming that the thermal fuse in the resistor block is the fuse protection for the blower motor. The rear blower is a 25amp fuse, but the front blower is a 10amp thermal fuse, that doesn't make sense, the front blower should draw more power than the rear.

I measured the resistance of the motor at 0.5 ohms, that seems low, in fact the lowest resister in the block was 0.5 ohms as well, if V=I*R, then the motor could draw as much as 12 amps, more than the thermal fuse rating. BUT, motors are inductive loads, so as the motor spins faster the resitance should go up. Anyone know a figure for the blower motor, other motors I've measured resistance on have been surprisingly low as well, so I'm not convinced that the blower motor is bad.

BTW, the air filter was rather dirty, but didn't look clogged, I blew it out with compressed air, some dust but not a lot. I'll try to get a fresh one tomorrow. The cut down airflow might reduce the cooling and raise the temp of the resistors, blowing the thermal fuse.

This post has been edited by Rick Anderson: 28 December 2005 - 02:01 AM

[Rick Anderson]

How about your cabin air filter? Did you replace that? A clogged filter would increase load on the blower motor and decrease air flow that goes over the resistor block and cools it.

A bad blower motor is my fear as well. The resistor block now has a "Thermal Fuse" in them, which was not included in the past resistors blocks. As well, it appears there is no conventional fuse for the blower motor.

SO, every time your blower motor blows a fuse, instead of replacing it with a $0.39 fuse, you have to replace it with a $30 Resistor Block, and throw away $28.51 worth of parts in the Resistor Block that is still good. Please someone correct me if I'm wrong on this, because I cannot find a conventional fuse for the Front Blower Motor.

I can see the logic of the thermal fuse, not only does the fuse blow if the current draw is too great, but it also blows if the temp of the fuse block gets too high. Which is how the resistor block modulates the blower motor, the resistance changes in the wires as they find a balance in cooling and current flowing by the temp of the coiled wires in the resister block.

My blower motor shows no sign of any problems, other than the resistance measurements at the connector is surprisingly low at 0.5 ohms. BUT, in my limited experience with electric motors, they always measure surprisingly low. They are inductive loads, meaning that resistance in the circuit increases greatly while it builds it magnetic fields, thus an electric motor once it starts spinning increases greatly in its electrical resistance. Same with coils for the ignition or relays. I believe for inductive loads, like motors, coils and relay actuater circuits, you only check that there is some resistance greater than 0, if its zero that indicates a short.

My fear is there is something wrong with my blower, if you replace a fuse for an electric item and it keeps blowing, you know you have a problem with the item or its circuit. Unfortunately with the 4th Gen Vans the Front Blower motor has a $30 fuse, pretty expensive to keep replacing fuses as you trouble shoot a "possible" problem with the motor.

I've replaced the thermal fuse in my Resistor Block. I'll post a new thread on it soon. I haven't tested it yet, but plan too tonight.

[caravanbob]

I'm really glad I found this thread...
I've got a 2001 GC with around 72K miles. Not 30 days ago (around 70K miles) I found I had only "hi" fan, and found the problem to be the resistor block. I replaced it (BTW, my local dealer is only charging me $15...some of you are paying WAY too much for it!) and all was well until this last weekend when temperatures dropped down to -15F, which is rather unusual for here. As a matter of fact, that was a record breaker, going back 20 or so years. During that cold snap, the resistor block died, and all I had was "hi". I brought it back to the dealer, and they did a warranty exchange for me, but they said if it blows again, they won't replace it unless I get an electrical system check ($60).
When the first one went, I measured each resistor to see if any of them had opened, and they were all fine. I did notice what I guess is the "thermal resistor" that has been described here, but I thought it was a diode.
Of course, the question is still, why did the second one go out so quickly when the first one lasted 70K miles? I've been told it's an indication that the blower motor is going bad, i.e. drawing too much power, causing the resistor block to burn out. I have not noticed any unusual noises, etc from the blower. As far as the fan itself goes, everything seems to be just fine, so I'm tending to discount that theory. Anyone have any opinions?
BTW, can someone post the actual Radio Shack part number for the heat resistor?
Thanks!

This post has been edited by caravanbob: 21 February 2006 - 06:20 PM

[alainb]

Hi,

Here is my little theory that I posted a few weeks ago on Rick thread:

.... what is the most damaging for the resistor is having the fan set at the lowest speed while the temperature control is set at high. At the lowest speed, all the 4 resistances are working, generating the maximum heat. During that time, the air flow is reduced to a minimum while his temperature is at a maximum. It must be very hard for the fuse!

.... for now on, as a preventive action, I will try to avoid using the lowest speed during winter.

Right or wrong? I don't know for sure!

Alain

[caravanbob]

Well, thats as good a reason as anything I can think of!

[danomite]

I just replaced my resistor block (2001GC). $14 at the dealer, said the new one was updated though it looked identical.

I just got my van used, no owners manual. Where is the cabin air filter? Thanks.

Since my van has rear heat/air, I'll follow alainb's theory and keep the fron air temp at luke warm, and get the primary heat from the rear heater.

[Tweety Bird]

alainb, on Feb 21 2006, 06:00 PM, said:

Hi,

Here is my little theory that I posted a few weeks ago on Rick thread:

.... what is the most damaging for the resistor is having the fan set at the lowest speed while the temperature control is set at high. At the lowest speed, all the 4 resistances are working, generating the maximum heat. During that time, the air flow is reduced to a minimum while his temperature is at a maximum. It must be very hard for the fuse!

.... for now on, as a preventive action, I will try to avoid using the lowest speed during winter.

Right or wrong? I don't know for sure!

Alain

Wrong.

The heat dissipated by the resistor is a function of voltage across the resistance times the square of the current. So if you double the resistance, you cut the power (heat generated) to 1/4 of what it was. But if you cut the resistance in half, the power quadruples. So, the setting that should be the hardest on the resistors would be the setting just below high, because that's the lowest resistance but the maximum current. Lowest fan setting would be maximum resistance but minimum current, so the heat generated would be much less.

I seriously doubt that the temperature of the air is a big contributing factor. A resistor gets much hotter than the air ever could, and while it can't cool as well with hot air as it can with cold air, I just don't think it would have a big effect unless the resistor or thermal fuse was marginal to begin with.

If the fan works well on high, it's -probably- not the fan motor. I'm not familiar with where the resistor is located on your car, but you need to make sure it's getting plenty of air from the blower.

But I'm guessing it's a case of poor quality parts.

[Gerry G]

I picked up a used blower moter from a boneyard for $15 but I have heard that some auto parts stores
do have them for $50 -$60.

Just as a note, it is a thermal diode which is essentially a fuse that will blow when is gets too hot. There
are three coils of wire which are the actual resistors, each coil being a different fan speed and HI does not
use any of the coils. If you notice, the fuse is centered between the three of them and if one of the coils
gets too hot it will blow the fuse. This makes the whole thing 'air cooled' so if not enough air is moving
over the resistor block, it overheats and blows the thermal fuse. On low speed the air speed is just
barely enough and if the motor draws any bit more than it should, it is likely enough for the coil to overheat
and blow the fuse.

Hope this helps,

Gerry G.

This post has been edited by Gerry G: 22 February 2006 - 11:27 PM

[gstringe]

I am getting into this issue late but as a note, the thermal fuse is not a diode but just a fuse that has a meltable thermal plug in it that will open the unit up if the temp gets too high.

I originally replaced the fuse in my 01 van with a Radio Shack unit and it held for a couple of years. I just replaced it a few weeks ago and it lasted a couple of weeks. I replaced it again with an NTE unit but it lasted only a couple of days. I have it temporarily bypassed with a wire and will replace it with a 25 amp unit I will order from MCM electronics. They are packages of 5 for $ 2.99 many choices of temps.

The Radio Shack and NTE units are rated at 10 amps continous and actually the fan draw 13-14 amps at the setting just below max so the 10 amp units should not really last very long.

I have changed the cabin air filter about 4 months ago and plenty of air flow. You might be interested to know that the resistor coil for the next to high speed will melt 60/40 solder in about 5 seconds if the air flow is removed. That is over 370 deg F.

[steve812]

Correct, it is not a diode. It is a thermal fuse. Some are designed in the normally open state and when they reach the temp limit of the fuse they melt and close and will provide HIGH only blower. Some are designed in the normally closed state and open at their set temperature. This appears to be an epedemic on the newer vehicles. I would also agree if the fuse is only rated at 10 amps then it's too low, most of all Mopar's blower systems have used a 20 amp circuit through the years. It appears that some of the part numbers for the resistor blocks have changed, maybe this means Mopar is trying to fix a design problem? I would like to keep abreast of this thread and any proper and safe fixes that are found to be reliable. I have ordered several years of resistor blocks to take a look at. I post on many Dodge forums and this problem always comes up. Here's some more info on the fuses, this is the most common manufacturer of the thermal fuse.

Micro-Temp


http://www.thermodisc.com/uploads/P-DSC-0099-2.gif

This post has been edited by steve812: 11 March 2006 - 01:53 PM

[alainb]

Hi,

To my knowledge, on the Caravan 2001, the thermal fuse do not close when it melt. It open, cutting the resistances circuit. For the high speed setting, the resistance circuit is simply bypassed.

On my van, the resistor has been changed by the previous owner after 2 years and 1/2 and I just changed it again after 2 more years. I don't make a big deal of it. After all, it is such an easy and cheap fix if I compare to other things that regulary go wrong in our vans, mainly for my van on the front suspension.

Would be nice if the resistor never fail but the safety device built in seem to do his job. On this tread, it is the blower motor that was probably the problem. But I must agree, as a fuse, the resistor is quite expensive.

Could somebody explain how to reach the cabin filter on a 2001 model? I don't have a clue on where it is and how to check it.

Thanks!

Alain

(Here is my old resistor. I bypassed the thermal fuse. It was working fine and I used it a few days but because of safety concerns I decided to install a new one instead.)

http://www.geocities.com/alaboux/resistor.jpg

This post has been edited by alainb: 11 March 2006 - 09:38 AM