Problem with fan blower ?

This is a 1997 Jeep Grand Cherokee. For about 3 months, my blower fan has
been intermittent, but it stopped running completely about ten days ago.
Before it stopped completely, sometimes I could bang on or around the fan
housing, and it would start (but only sometimes). Perhaps this was
coincidental, but I got it to start several times by doing this.
Naturally, I thought that my motor was bad, although it was replaced 18
months ago.

I checked the 40 amp fuse with an ohm meter, and it is ok. I took the fan
out, and much to my surprise, it will run when hooked up directly to a 12
volt battery.

When the fan would work sometimes and would not work at other times, it was
an all or nothing proposition. In other words, it would not run at any
speed setting.


Could this be a bad resistor pack ? Is there a way to check the resistor
pack ?

Any other ideas on this ? I am stumped, and any help would be
appreciated.

Thank you.

Jmaes

James wrote:
> This is a 1997 Jeep Grand Cherokee. For about 3 months, my blower
> fan has been intermittent, but it stopped running completely about
> ten days ago. Before it stopped completely, sometimes I could bang on
> or around the fan housing, and it would start (but only sometimes).
> Perhaps this was coincidental, but I got it to start several times by
> doing this. Naturally, I thought that my motor was bad, although it
> was replaced 18 months ago.
>
> I checked the 40 amp fuse with an ohm meter, and it is ok. I took
> the fan out, and much to my surprise, it will run when hooked up
> directly to a 12 volt battery.
>
> When the fan would work sometimes and would not work at other times,
> it was an all or nothing proposition. In other words, it would not
> run at any speed setting.
>
>
> Could this be a bad resistor pack ? Is there a way to check the
> resistor pack ?

You have the basic AC? If you have automatic climate control the
system is different and doesn't use a resistor pack, it uses a control
module (solid state relay).

Usually when it goes you can tell from the scorch marks, but it pins out like this.

1--resistor--4--resistor--2--resistor--3

Pin 3 feeds the blower motor and also runs back to the speed control
(full speed bypasses the resistor)

I don't have specs for the resistor block, other than if it's open
it's dead.

Not running on max can indicate a few other things. Bad connections for
one. The thing is those wires can get melty and the connectors then back
off and fail. Take a close look at the pins and wires.

Since banging fixed it I'm leaning towards bad connectors. The arc would
create a small spotweld that would last for a while but get real hot.


--
DougW

"James" > wrote in message
...
> This is a 1997 Jeep Grand Cherokee. For about 3 months, my blower fan
> has
> been intermittent, but it stopped running completely about ten days ago.
> Before it stopped completely, sometimes I could bang on or around the fan
> housing, and it would start (but only sometimes). Perhaps this was
> coincidental, but I got it to start several times by doing this.
> Naturally, I thought that my motor was bad, although it was replaced 18
> months ago.
>
> I checked the 40 amp fuse with an ohm meter, and it is ok. I took the
> fan
> out, and much to my surprise, it will run when hooked up directly to a 12
> volt battery.
>
> When the fan would work sometimes and would not work at other times, it
> was
> an all or nothing proposition. In other words, it would not run at any
> speed setting.
>
>
> Could this be a bad resistor pack ? Is there a way to check the resistor
> pack ?
>
> Any other ideas on this ? I am stumped, and any help would be
> appreciated.
>
> Thank you.
>
> Jmaes
>
>

The Fan Switch is a three- or four-position thingy -- LO, MED, and HI, or a
variation on that theme -- and the speeds are controlled by a resistor. The
resistor is toast. (Actually, it's toasted. It gets hot by design, and toast
is a logical outcome of cooking.)

Let's say for the sake of illustration that the circuit has 20A available.
On HI, all 20A are fed to the blower motor (which does not care if it is
blowing warm air or cold air into the cabin). On MED, for example, perhaps
there is only 12A, and on LO there is only 5A. (I don't know or care that
the numbers are right, I'm illustrating the circuit, not designing it.)

The different currents are provided by putting a resistor into the line to
block (absorb) current, and pass the remainder to the motor. If you remember
Ohm's Law, voltage, resistance, and current, are all interrelated. If there
is X current available at a particular voltage, then the voltage that is
applied to the load can be capped by substituting the resistance in the
circuit. The motor wants 12V, but if the resistance is increased, the
voltage drops because current (loads, which is also resistance) before the
motor are increased, and the motor slows down.

Normally, when the resistor fails in the blower motor circuit, HI speed
remains after the lower speeds have stopped working. It is possible that HI
speed will fail too, but normally you will notice that HI remains until the
very last.

James writes:

> Could this be a bad resistor pack ?

Yep, most likely culprit in my experience.

Same thing happened on my wife's 2005....

--


People run on Windows, animals on UNIX.
That explains it all!

"James" > wrote in message
...
> This is a 1997 Jeep Grand Cherokee. For about 3 months, my blower fan
> has
> been intermittent, but it stopped running completely about ten days ago.
> Before it stopped completely, sometimes I could bang on or around the fan
> housing, and it would start (but only sometimes). Perhaps this was
> coincidental, but I got it to start several times by doing this.
> Naturally, I thought that my motor was bad, although it was replaced 18
> months ago.
>
> I checked the 40 amp fuse with an ohm meter, and it is ok. I took the
> fan
> out, and much to my surprise, it will run when hooked up directly to a 12
> volt battery.
>
> When the fan would work sometimes and would not work at other times, it
> was
> an all or nothing proposition. In other words, it would not run at any
> speed setting.
>
>
> Could this be a bad resistor pack ? Is there a way to check the resistor
> pack ?
>
> Any other ideas on this ? I am stumped, and any help would be
> appreciated.
>
> Thank you.
>
> Jmaes
>
>
>

Steve R. wrote:
> Same thing happened on my wife's 2005....

Fairly common problem, not exactly a cheap part for what it
is though. :/

http://www.teamgrandcherokee.com/AC_...ing/index.html
http://www.jeepsunlimited.com/forums....php?p=4568740


> "James" wrote ...
>> This is a 1997 Jeep Grand Cherokee. For about 3 months, my blower
>> fan has
>> been intermittent, but it stopped running completely about ten days
>> ago. Before it stopped completely, sometimes I could bang on or
>> around the fan housing, and it would start (but only sometimes).
>> Perhaps this was coincidental, but I got it to start several times
>> by doing this. Naturally, I thought that my motor was bad, although
>> it was replaced 18 months ago.
>>
>> I checked the 40 amp fuse with an ohm meter, and it is ok. I took
>> the fan
>> out, and much to my surprise, it will run when hooked up directly to
>> a 12 volt battery.
>>
>> When the fan would work sometimes and would not work at other times,
>> it was
>> an all or nothing proposition. In other words, it would not run at
>> any speed setting.
>>
>>
>> Could this be a bad resistor pack ? Is there a way to check the
>> resistor pack ?
>>
>> Any other ideas on this ? I am stumped, and any help would be
>> appreciated.
>>
>> Thank you.
>>
>> Jmaes