1990 Chrysler A/C Blower

Although the blower motor may be drawing too much current, I would suspect
that the harness connector to the ignition switch has a terminal that has
excessive resistance.  Any unwanted resistance becomes a heater element when
current flows through it. Check the connector carefully for any signs of
melting around the terminals and make sure each terminal is clean and making
good contact. Some times the wire itself gets a bit brittle near the
terminal that has too much resistance, so you might check closely to see if
the wires  look ok as they go into the connector.   To check the circuit
current, you could use a multimeter with a setting for checking amps, but
make sure it is one that can handle the amount of current the motor might be
drawing.  Most of them only go up to 10 AMPS and the blower motor probably
draws more than that.  I'm not sure exactly what the specs would be for your
model.  Maybe someone else here has that information handy.

Another way to check for unwanted resistance in the terminal is to perform a
voltage drop test across the connection. If you have a volt meter and need
instructions on how to do this, just post back with your request.

You might also want to check to see if there are any factory TSB's or
recalls that apply to your model.  Quite a few models have been recalled for
ignition switch problems that can even lead to starting a fire. Sorry I
don't have access to any repair information with TSB's or recalls listed (at
least not until Monday). Maybe someone else here has a resource for that and
will check it for you.
--
Disclaimer:
Due to the nature of solving problems over the internet being mostly
guesswork,
please do not consider the above recommendations as the only possible
solutions.

--
Kevin Mouton
Automotive Technology Instructor
"If women don't find you handsome, they should at least find you handy"
Red Green

I think you just might be onto something. The connector did look a little
suspect to me when I replaced the switch. Thank you for your response, and
please post the instructions for the voltage drop test, and what the results
tell me.
Oh, does it help in the diagnosis if the switch gets hotter as the speed of
the motor increases? By the way, this model has the Automatic Temperature
Control if that helps ...

Thanks, Kevin!

Dennis


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That doesn't really change the diagnosis.  What I suggest you do is clean
the contacts and, if convenient, measure their resistance.  But mostly just
deal with it visually; make sure they're clean and make good contact.  If
you can pinpoint where the heat is coming from, so much the better; that
*is* your resistance test.

Checking voltage drop is very simple. The theory that applies is that when
electrical current passes through a resistance, there will be a drop in
voltage (and heat will be produced). The formula for caculating voltage drop
is (Voltage drop = Amps X Ohms).



To check the voltage drop across the terminals in an electrical connector
you would use a volt meter set to your meter's scale that is best for the
car's 12 volt system.  Most meters have a 0 to 20 volt range that should do.
Turn on and make sure the circuit you are testing is working. In your case
that means turn on the ignition switch and turn on the Heater blower motor.
Identify witch circuit in the connector feeds the accessories which include
the blower motor (or why not just test all the terminals while we are
there?). Back probe the wire going into one side of the electrical connector
with the positive lead of the meter, and back probe the same circuit where
it comes out the other side of the connector, with the negative lead of the
volt meter.  Back probing means to insert the tip of the meter lead probe
along side the wire going into the back of the connector (harness side)
until it contacts the metal wire terminal that the wire is crimped into.
Some times you have to use a paper clip or something to reach far enough
into the connector hard shell to make contact with the metal terminal.  One
you have both leads connected (one on each side of the connector) observe
the volt meter reading. Don't forget that there has to be current flowing
through the connector on the circuit you are testing. Any reading on the
meter is the amount of voltage being dropped off by any resistance between
the two meter leads. Simply stated, if the meter reads 1 volt then you are
loosing 1 volt due to resistance. Of course, the ideal reading would be 0.00
volts, but anything up to about 0.3 volts would be acceptable in this case.
Anything more than that and you have found excessive resistance in the
connection that will cause heat to be generated when ever the current is
flowing. The amount of heat will be proportional to the amount of resistance
and total circuit current. at a given source voltage. In other words. At 12
volts the resistance in the connector will get hotter when the fan is on
high speed because there is more current flowing across the resistance.

For example: If the blower motor current is 10 amps and the battery voltage
is 12 volts then a voltage drop of 1 volt means there is 1 OHM of
resistance.  The formula is (Voltage drop = amps X ohms) or 1=10X1. Like I
said, you really don't want any resistance in a connection, so the preferred
voltage drop would be 0.0 volts, but the larger the voltage drop, the higher
the resistance will be, as long as the applied voltage and current remain
the same.

Sorry for the long rant for a simple test, but I am used to explaining this
kind of stuff to my students who know basically nothing at the time.

--
Kevin Mouton
Automotive Technology Instructor
"If women don't find you handsome, they should at least find you handy"
Red Green

Thank you very much for this information. I really appreciate it. I will
check the voltage drop on Saturday.
No problem about the explaination.. I appreciate the rationale behind the
test.

Dennis

Kevin wrote:

It also might be instructive to explain that the heat that you mentioned
is calculated by the following formulas:
watts (heat generated) = amps^2 x ohms = volts^2 ÷ ohms = volts x amps
(will get same results regardless of which formula you use)

Also, you might teach your students that when units are named after a
person, when written out, they are not capitalized, but when
abbreviated, they are capitalized (volts, amps, ohms, watts, V, A).  :)

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

I uncovered my ignition switch and the connector dead ends there. I cannot
backprobe the ignition switch side of the connector. I can see, though,
where the connector has gotten hot, and I found the wire that gets hot when
the blower is running. There is 0 Ohms resistance. Could there be 0 Ohms
resistance but still be voltage drop? Is there some other way to measure the
voltage drop, or am I just screwed? Thanks for your input!!! I have pics of
the connector that I can email to you if you would like.

Dennis

D. Smith wrote:

Nothing is 0 ohms, but the voltage drop will be proportional to the
resistance as Kevin explained earlier.


Yes - simply put the meter in dc voltage mode and read volts across the
suspected connection with the blower running.  It will probably rise as
it heats up.



The typical kind of meter can't measure low enough resistance to
determine if there's a problem there or not.  For example - lets say
your blower motor pulls 10 amps on hi speed, and you have 1/2 ohm
resistance all concentrated at a point connection.  That would mean that
a very small mass of metal is getting heated with 5 watts.  5 watts
doesn't sound like much, but when it's concentrated in an almost
infinitly small mass, it is a lot - temperatures go up.  The more the
temperature goes up, the more the resistance, the hotter it gets.  But
you're only measuring when it's cold and with a meter that can't read
sub-ohm levels.

In this case, screw the meter readings (though you could read the
voltage drop across the suspected area as you suggest), and go by the
physical signs that it is overheating.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

OK, I did the following.. I backprobed the wires in the connector with the
hot wire to the ignition switch connector with the blower running, and I had
two wires that register voltage. One registered about .3 volts, but the
other registered .7 volts. both of these wires were heating up. If this is
an indication of excess resistance, what would my next step be? I really
appreciate the input on this. It has been 'driving' me nuts for quite a
while.

Dennis

D. E. Smith wrote:

The solution would be to replace the section of wire that is high
resistance, including any that may have been damaged by heat.  If you
don't feel competent in making good, reliable, low-resistance splices,
you need to pay someone to do it or enlist the aid of a friend who is
qualified - otherwise the problem will repeat itself in the new splice.

There's a chance that the joint that is high resistance can be made low
resistance (without making any new splices), but that would have to be
evaluated (by someone competent).

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

See reply at bottom



I see , your ignition switch wiring harness connector plugs directly on to
the ignition switch so you do not have a harness connector that separates in
two halves. The voltage drop you would measure would also include the
contacts in the switch itself in your case, so it is difficult to determine
weather the heat is coming from the harness connector terminal or the
ignitions switch internal metal connector. But, you did say you replaced the
switch with a new one (didn't you?), so it is probably not the switch itself
that is causing the problem.

The bottom line is that where there is heat there is resistance. The hotter
it gets the more resistance it will have and therefore the more heat it will
produce, You have found a place that has resistance where it should not be,
because you can tell that it is getting hot. The repair can be made in
several ways. You can purchase wire terminal repair kits, but it is very
hard to find the exact one for your application. You may be able to get it
from a dealer, or even a complete connector repair kit, in some cases. If
that is not available, you may be able to take apart the connector and
remove the crimped on terminal from the wire, clean it, tighten it up, and
solder it back to get rig of the resistance. Some times the resistance is in
the terminal crimp on to the wire, but sometimes it is just from corrosion
or even a loose fit where the metal female terminal fits on to the male
terminal.  Someone with a lot of experience repairing wiring harness
connector terminals cold probably do the job, but iof you do not have the
expertise, so your best bet is to try and find a replacement harness
connector, either as a new part from a dealer or maybe even one cut off of a
salvage vehicle.

Now, having said all that. keep in mind that the amount of heat produced is
proportional to the current passing through the terminal. If the blower
motor is actually drawing too many amps then it might heat up even a new
terminal. The other part of making sure this turns out to be a good repair
is to also make sure the blower motor is not drawing too many amps..

Also, be sure to check for factory TSB's or recalls. On some models it is  a
known problem that the switch itself is the culprit and a newly designed
replacement is available to correct the problem.

--
Kevin Mouton
Automotive Technology Instructor
"If women don't find you handsome, they should at least find you handy"
Red Green

How can I determine if it is the motor that is causing the problem or not? I
would like to rule the motor out before I go ripping wires out. The ignition
switch has been replaced, so I assume that if there were a replacement due
to a TSB, I would already have it. Would it be safe to say that if the wire
gets cooler as I get away from the connector, the problem is the connector
and not the blower motor? Thanks very much for your input!!

Dennis