I have a 1995 E320 (W124) with a really strange Automatic Climate Control System Fan (Blower) issue.


As most of you know, with this model's Automatic Climate Control System there are three push button switches for the fan: High, Auto, and Low. If my fan is in the High position, the system works fine, but of course the fan is on high all the time and about blows the air off one's head. All. The. Time.


In this situation, the automatic temperature regulation and the way the system automatically decides which vents should blow air (lower, middle and defrost vents) works fine. Cabin temperature reaches and remains at what I set the temperature dial wheel to, and the air gets directed where it's needed (more toward the windshield if demisting is needed, etc.). It's a brilliant design, especially considering it is now nearly 30 years old. But that fan noise!!!


BUT: If either the Low or the Auto fan buttons are pushed, the fan stops working completely. Not right away - it takes it a little time to slow down and then stop. At this point, to get it to work again, one must do the following:


1) Turn the car off for a bit (10 seconds or more).


2) Push the High button on the fan.


3) Turn the ignition key to the ON position (but do NOT actually start the car).


4) Wait a few seconds and the fan will come on.


5) Go ahead and start the car, and the fan will continue to run (on High).


As long as the fan switch is then left in the manual High position the fan will then keep running. All day even on a cross country trip.


If while driving as above with the Fan in the High position, the fan's Auto button is then pushed, the fan does not just immediately stop working. It runs on high for a few seconds, and then one can hear it switch down to the next slower speed which it will maintain for a few seconds, then it progressively slows to each of its slower and slower speed settings, until it stops. This takes a total of about maybe 20 to 30 seconds to happen. And then of course, once it has completely stopped, the only way to get it to work again is to follow the steps outlined above.


Note, that if on is trying to get it to work again, just turning the car off, setting the fan to the High setting and starting the car normally does not work. The fan will not come on. The only way to get it to come back on is to turn the key to ON but NOT start the vehicle, and wait until the fan comes on (usually takes about 2 to 3 seconds, and THEN one can crank the engine and start the car, and the fan will continue to work. I can only surmise that the reason for this is that for some reason the system "needs" slightly lower voltage coming from just the battery to "reboot" the fan and that the full 14.4 volts supplied by the alternator with the car running is just too much for the "reboot" to happen.



I think the problem is either in the Control Module or the Blower Motor Resister (the one that is under the blower motor which itself is under the entire windshield wiper/motor assembly).


Either of these parts is expensive, so I do not want to be chasing the problem by throwing parts at it.


Any ideas? I would really appreciate any help and/or suggestions!



Thanks in advance,


John

The porcupine or resistor is a power transistor which is terminated at the firewall by a 3 prong plug. The 3 wires are powered, ground and control voltage. The control voltage 1 to 5 volts controls the fan speed. That's where I'd start diagnostics. On a side note check your auxillary water pump and see how much current it uses or if it even works. High current > 1 Amp will cause your CCU to do funny things.

__________________
92 e300d2.5t
01 e320
05 cdi
85 chev c10

Thanks for the suggestions.



Is the plug for the resistor accessible to check voltages without removing windshield wiper system and the blower?

And regarding the auxiliary electric water pump, I did not know the car had one! I have a multi-meter so I should be able to check it's amperage draw. Could you tell me where approximately it is in the engine compartment? Perhaps front of the engine or near the radiator? Thanks.

The 3 prong plug is behind the brake booster in the engine bay.

__________________
92 e300d2.5t
01 e320
05 cdi
85 chev c10