Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help




Go Back   PeachParts Mercedes ShopForum > Technical Information and Support > Tech Help

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 07-10-2003, 01:35 PM
Registered User
 
Join Date: Dec 2001
Location: Rocklin CA
Posts: 65
Fan Voltage on AC unit

My fan speed regulator went out months ago and I had it replaced. Everthing works OK now except the fan doesn't seem to blow hard enough. When I check the voltage through the front panel it won't go higher than 4.8. This is on my 96 S-500. On my 98 430E it goes to 6.0. Looks to me to be the same units. What should the s-500 go to? IF I'm not there is there anything to do? I've manually put the AC to "LOW" and maxed out the fan speed. 4.8 is it.

KG
__________________
Ken G
96 S500 79K (great white whale)
98 E430 80K Sports Package (gray ghost)
Reply With Quote
  #2  
Old 07-10-2003, 09:53 PM
JimF's Avatar
'94 S500: only 793 sold!
 
Join Date: Mar 2001
Location: San Diego, CA
Posts: 1,925
Sorry to say that it . . . .

sounds like the blower regulator is gone again.

Not sure of the numbers but it blower should go from hi to low speed as you spin the dial (Min - Auto - Max).

Maybe good news it's still under warranty. Also make sure that the 'white' grease make good contact with the blower's housing to dissipate the heat in the regulator.
__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page
Reply With Quote
  #3  
Old 07-12-2003, 08:58 AM
KenP's Avatar
Registered User
 
Join Date: Dec 2002
Location: Southern New Hampshire
Posts: 418
Voltages are same as mine.

Ken,
Went out and checked my 1996 S500 Coupe...
You're reading out the blower voltage on your climate control pushbutton unit, right?
Service manual says maximum of 6 volts.
My S500 blower works great; lots of air through the vents. When I manually max out the blower fan speed, my reading is the same as yours... 4.8 volts.
Next step down is 3.2... and then down from there.
My A/C and blower work fine. I think you're OK electrically.
There are a number of pushbutton units (starting in '96) that LOOK the same, but they are not... so, you can't go by that.
If your vent flow rate is low, its probably something else. How long since you changed your main filter? or, maybe you need to replace the blower motor itself. I replaced mine recently (it started to squeek/squeel) and the flow was much improved.
Hope this helps, KenP
Reply With Quote
  #4  
Old 07-12-2003, 02:27 PM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
The real way to test your problem is to evaluate the voltage drop from the blower neg side to ground. When in high blow the drop should be less than 1v. In theory it should be zero but you are dealing with a transistor amplifier and it does not become a perfect conductor.

The regulator regulates by closing the ground side of the circuit. If you watch this voltage drop it will be over 6v at low speed and drop as the speed increases.
__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
Reply With Quote
  #5  
Old 07-13-2003, 08:17 AM
KenP's Avatar
Registered User
 
Join Date: Dec 2002
Location: Southern New Hampshire
Posts: 418
Steve, can you explain a bit more? I certainly understand regulating the speed of the motor by varying the ground side/path of the motor, but something doesn't add up.
If the voltage drop to ground is 1 volt or less at high speed, what is the "blower motor voltage" shown in the diagnostic mode of the climate control head? Maybe its not really blower motor voltage?
If hot side is 12-14 volts, how can "blower motor voltage" only be 4.8 volts with a 1 volt drop?
Thanks much, KenP
Reply With Quote
  #6  
Old 07-13-2003, 09:27 AM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Well I planned on writing you a private answer since today I am not feeling very generous, but your profile states you won't accept email from the group. Since such access is the reason I don't feel generous this morning I leave it unsaid.
__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
Reply With Quote
  #7  
Old 07-13-2003, 11:34 AM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
At least you are protected from random violence, maybe I should consider being anonomous. But, I am over it and I am sorry, so here is your answer.

The voltage given in the display is the control voltage. if you made the circuit into an amplifier transistor device this voltage would be the base biasing voltage. The transistor then would alow current to flow in proportion to the bias strength. Transistors are used as amplifiers or switches. In this case they are being used as an amplifier.

The voltage I was mentioning; the voltage drop between the blower ground and real ground is a measurement of the level of amplification. If the transistor was at high blow there would be theoretically no voltage drop as the ground of the motor would be pulled all the way to ground. In low blow the blower ground is only pulled to maybe 6v. The regulator/transistor looking like a resistor to the circuit.

The test is easy as the blower circuitry is easily accessible under the large plastic cover at the rear of the engine compartment. There you can verify that the bias voltage displayed on the pushbutton controller is the actual voltage seen by the regulator AND using the voltage drop method one can see how the regulator responded to command.
__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
Reply With Quote
  #8  
Old 07-13-2003, 08:50 PM
KenP's Avatar
Registered User
 
Join Date: Dec 2002
Location: Southern New Hampshire
Posts: 418
Thanks

Steve,
Thanks. Not sure I entirely understand, but I'm going to pull the schematic and see if I can noodle it out with your added help. I'm a professional engineer by training... the way these cars are laid out electrically and mechanically interest me... which is the primary reason I bought one.
Don't understand why you ran into a mail problem with my profile. Others have sent me mail. Something must have changed... I'll check. Anyone can reach me direct at gearhead285@hotmail.com.
No intention of trying to stay unknown to the group or anyone else for that matter.
Regards, KenP
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 05:22 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2011 Pelican Parts - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page