Defrost blower switch

[jeffc280sl]

Took the heater/defrost blower motor out for cleaning while recovering the dash.  Now that it is fresh and oiled it does not shut off.  At the full anti-clockwise position the motor runs at a very very low speed.  Going clockwise the motor speed increases and just before the full clockwise position you can feel a click in the knob and then the fan speed is at full.

The wiring diagram seems to indicate that this is correct.  I don't think the fan rotated at all at the full anti-clockwise position prior to cleaning.  This may have been due to dirt/crud in the motor and on the brushes.

Can anyone confirm proper operation of the switch and fan?

Thank you

Jeff C.
1970 280SL 4-speed

[bpossel]

Hi Jeff,

When I rotate my switch counter clockwise it operates on slow speed.  As I continue to rotate counter clockwise at some point it "clicks", then the fan operates at a higher speed.  In summary, my switch has 2 speeds.

Regards,
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[jeffc280sl]

Thanks Bob,

The speed if my fan can be varied by turning the knob. After the click at the full clockwise it is at 100% max speed.  However it never shuts completely off which I guess is the same operation as you are describing for your fan.

Jeff C.
1970 280SL 4-speed

[A Dalton]

Good Question..

 I have schematics from early 042/043 showing an OFF position w/indicator lamp circuit for blower switch.
 I also have early .044 showing OFF position , but the indicator lamp as been eliminated.
 I also have 280SL/8 showing same.
 Possibly late .044 had no OFF , but the early 113s show it on schematic. From rotation start to end CW, they show Off,Variable[phase I] , and High [ phase II ]....definite click on II

[jeffc280sl]

Thanks for the info.

The wiring diagram in the BBB does not clearly indicate an off position for the switch.  It shows the variable function for phase I and the full on position for phase II.  Any other inputs out there?

Jeff C.
1970 280SL 4-speed

[bpossel]

Jeff,

When my switch is in the off position (fully clockwise) I dont hear the fan.  So, I assume its off?  I'll look closer at mine today.  It's rainy today in Memphis, so a good day to some inside work.  I need to remove my switch anyway and see if my bulb is dirty or just bad.  No switch light at night.
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[jeffc280sl]

Bob,

When my switch is at full CW the fan is on full.  I think the lighted switch is for earlier versions than your 71 and my 70 280SL.

Jeff C.
1970 280SL 4-speed

[A Dalton]

Just checked my .043 and there is not only an OFF position, but It has a click detent at that position [ along with one on the High setting.]
 CW full is High, CWW full is OFF.
 I do not think I have ever seen a High fan position at full CCW and Off at Full CW.. [ maybe LHD ??]
 My 280 schematic does show the Off position of the switch swipe/contactor. It is shown as a line with knob on it and is off the variable resistor in the switch.
 Possibly you have not turned the knob all the way to the OFF detent
 ..

[bpossel]

OK, going from memory is not good, esp when you get older....

Just went out and checked my switch.  CW turns it on.  CCW turns it off.  Mine only seems to have 2 speeds, low and high.  High when fully CW and the click is heard.

Sorry for the error!
B.

bpossel
Memphis, TN.
1971 280SL
1997 E320

[A Dalton]

Originally posted by bpossel

OK, going from memory is not good, esp when you get older....

Just went out and checked my switch.  CW turns it on.  CCW turns it off.  Mine only seems to have 2 speeds, low and high.  High when fully CW and the click is heard.

Sorry for the error!
B.

bpossel
Memphis, TN.

 B,
 That sounds correct .. I think is you listen real good , you will see that the low speed is actually a variable low speed. As you slowly turn the knob CW you will hear the slightest speed increase with the increase in the knobs CW position.  This is only on the low speed section of the switch, which is the resistor/swipe contactor circuit. Once you get to the Click, the switch is just a straight contact that allows full battery voltage to blower [ no resistor circuit]. So, the switch has two circuits.. one rheostat resistor circuit for low variable speed and one single switch contact for full 12v to accomplish high speed.
 Does your switch have NO fan when turned all the way CCW ??
Tnx

[A Dalton]

Here is one just listed.. Earlier style with indicator lamp

 http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7955271177&category=6763

[jeffc280sl]

I looked into my defrost switch some more and discovered some play in the shaft which does not allow the vaiable speed contact plate to move to the full off CCW position.  The plate stays just on the end on the resistor spring and never fully rests on the ceramic end point for off.  It's defective and I'll replace it some day.

Thanks for the help.

Jeff C.
1970 280SL 4-speed

[jeffc280sl]

I started reassembling the dash and took another look at the defrost switch.  Due to some play the contact plate did not return to the full off position and because of this the fan would not turn off and ran at a very low speed instead. I did not previously notice this because the motor was grimy and wasn't free moving enough to spin at the lowest setting anyway. I cleaned the motor and decided to see if I could put a small dab of epoxy on the end of the resistor spring so that when I turned the switch to the off position the contact plate would ride up on the epoxy and break contact with the spring.  It worked out great and now my switch shuts down the fan motor.  It should last a good while, I hope anyway.

Jeff C.
1970 280SL 4-speed

[JPMOSE]

I meant to post a strange finding a couple of years ago but forgot until now.  When I first obtained my 250SL in January 2006, my blower switch knob had to be replaced because the rubber rim was deteriorating.  My car is a very early 1968 model year (produced in July 1967) so it has the safety knobs on the radio, lighter, blower switch and window cranks.  OK...HERE IS THE STRANGE FINDING: My original knob has a hole in the center along with a working light on the blower switch!  Yet, it is the later wide safety knob.  Of course, the replacement knob didn't have the hole in it (but was otherwise identical).  I bought the car from the original owner and I highly doubt she would have modified the knob (certainly wouldn't have cared).

Has anyone else seen the early wide knobs (starting in model year 1968)with a hole for the fan light?

Only a collector would find this remotely interesting!!!

Best Regards,

J. P. Mose
1968 250SL
1987 560SL