rsacheli

Like others have identified, my front fans cease to operate when moving heater control from blue to red. After a couple of seconds of fan operation, the cease to run. Heat can be felt, faintly through the air ducts.

I have tried all of the suggested techniques, but have a situation which has not yet been described.

Here is the troubleshooting and results....

1. The rear blower fan fuse is good.
2. I detected an open circuit in the rear blower resistor, so I replaced it with a new one.
3. I removed the relay and swapped it with the A/C relay, but did not detect any change in function.
4. I removed the relay and jumpered #2 to #7.

#1 on plug/85 on relay = control "signal" for fast-speed.
#2 on plug/30c on relay = goes-in 12V power for slow-speed.
#3 on plug/30 on relay = goes-in 12V power for fast-speed.
#4 = not used.
#5 on plug/87 on relay = goes-out 12V power for fast-speed.
#6 on plug/85c on relay = control "signal" for slow-speed.
#7 on plug/87c on relay = goes-out 12V power for slow-speed.
#8 on plug/86 on relay = control power.

5. Using a voltmeter, I detected the following voltages at the following locations:

With the ignition on, but the car not running.
a. On the one side of the rear blower resistor - 0 Volts
b. On the other side of the rear blower resistor - 0 volts
c. On one side of the plug which attaches to the temperature sensor - 5 volts
d. At the power plug feeding the blower motor - 0 Volts.

6. I then tested the same testpoints w/ the power plug disconnected from the motor and found the following:

a. On the one side of the rear blower resistor - 12 Volts
b. On the other side of the rear blower resistor - 12 volts
c. On one side of the plug which attaches to the temperature sensor - 5 volts
d. At the power plug feeding the blower motor - 12 Volts.

After performing the same tests after jumpering #3 and #5 and getting the same results, I suspect the rear blower motor is bad.

7. I then proceeded to test the same testpoints w/ the relay installed (instead of using jumpers) and found the following:

Once again, with the ignition on, but the car not running.
a. On the one side of the rear blower resistor - 0 Volts
b. On the other side of the rear blower resistor - 0 volts
c. On one side of the plug which attaches to the temperature sensor - 5 volts
d. At the power plug feeding the blower motor - 0 Volts.

So - Suspecting that the relay may have gone bad when the motor stopped working I swapped the relay with the one from the A/C from the luggage compartment; which is operating correctly and I think is good.

8. Once again, with the ignition on, but the car not running, I found the same voltages as identified above.

a. On the one side of the rear blower resistor - 0 Volts
b. On the other side of the rear blower resistor - 0 volts
c. On one side of the plug which attaches to the temperature sensor - 5 volts
d. At the power plug feeding the blower motor - 0 Volts.

9. At this point, I was thoroughly confused and attempted the same test but this time I started the car, placed the temperature setting on 27 and engaged the defroster button.

The voltages were:
a. On the one side of the rear blower resistor - ~0.6 Volts
b. On the other side of the rear blower resistor - ~0.6 volts
c. On one side of the plug which attaches to the temperature sensor - ~5.5 volts
d. At the power plug feeding the blower motor - ~0.6 Volts.

Any attempts to re-attached the power plug to the motor brings all voltages to 0 volts - so there appears to be a short in the motor. However, I am not sure what would cause the situation w/ the relay inserted. I would have suspected to see the 12 volts at each point noted above once the plug was removed from the motor and the relay installed.

Does anyone have any ideas for me to try?

Bearclaw

Take it to a shop?

Sorry , I don't have the time, patience (or aptitude ) to do all the diagnosics you've done, but I have the exact same behavior and would love to hear what your outcome is...
My fans also will randomly start for a second or two if the temp dial is left off of the blue dot, but there is no discernable pattern.

Rocket Rob

My car had a similar set of symptoms with my defroster. Sometimes it would start the fans and then stop after a few seconds. Eventually, I got tired of it and took it to the dealer. The problem was a defective fan. They said that when the rear fan stops blowing the blowers in the dash automatically shutdown. Not sure if that is true or not. However, I can say that since replacing the rear fan, the defroster and heater worked perfectly.

Bearclaw

Rob, do you recall what the cost-damage was on that repair???

Rocket Rob

Barry - Its been several years but I would guess it was around $500. You can't seem to leave the dealer's service department for less these days.

C4Russ

I had the rear blower motor fail, actually it hadn't failed yet, it was just noisy and the bearings were shot. I replaced the motor for a very reasonable price.

Get Cool Parts

Bearclaw

Looks like I've found my first P-car repair project!

puma1824

Was this a pretty easy fix? Is the link you provided a direct swap?

ldl311

I have the same problem with my front fans, (blue dot / red dot), but my rear fan cycles on and off. Interesting that the two might be tied together. Has anyone had an issue with the rear fan cycling? Would that be a resistor problem?