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-Benz Forum > Mercedes-Benz Tech Information and Support > Mercedes-Benz SL Discussion Forum

LinkBack Thread Tools Display Modes
Old 02-21-2010, 05:10 PM
Registered User
Join Date: Feb 2010
Location: Spring, TX
Posts: 17
Climate Control Unit Fault or Blower Control Module Fault?

I have an '87 560SL with climate control issues. The blower does not work at all. When driving I can feel hot and cold from the vents corresponding to temp setting but I have no blower fan at all. I have eliminated the blower unit as it works fine with 12V directly applied to the terminals on the firewall socket. I have the Mercedes workshop manual CD for the car and yesterday I ran through the climate control check procedure and have concluded it is either the push button unit in the dash or the blower control unit behind the glovebox. The procedure says it could be either unit, which is not much use to me. Does anybody know of any checks I can carry out to determine which unit is at fault?

Reply With Quote
Old 02-21-2010, 05:22 PM
Join Date: Oct 2004
Location: NC
Posts: 3,202
Best guess is push button but only a guess.

To see my 129 parts for sale visit:
John Roncallo
Reply With Quote
Old 02-21-2010, 07:16 PM
Registered User
Join Date: Feb 2010
Location: Spring, TX
Posts: 17
Thanks. Doing a bit of research it would seem the push button units are unreliable on these cars so I would tend to agree. Is it unusual for the blower control unit to fail? Also, do I have to source a replacement push button from a 107 or will units from other models also work? The same looking unit is fitted on quite a few other models around that year.
Reply With Quote
Old 02-22-2010, 07:38 PM
Strife's Avatar
General Purpose Geek
Join Date: Apr 2004
Location: KY USA
Posts: 2,238
It's going to be difficult to determine the fault without known good substitution replacements or a voltmeter and the schematic, which on the CD service manual.

As bizzare as this sounds, jiggle the key in the ignition (but read below about temperatures first). I have found a bad ignition switch to cause no power to get to the CCU (and therefore, blower control).

The blower control unit is basically a box of power transistors that switch various resistances in the "plug" end of the blower motor on and off and is not likely to entirely and completely fail.

Caution: Many of the climate control units LOOK the same but are quite different electrically. For example, the 85 CCU and 86 CCU look alike at first glance, but are electrically different and not interchangeable because the older design would tend to pop transistors if the auxilliary water pump failed. I think it provides +12 to the pump, the newer one switches ground.

There are a lot of interconnected parts here. I don't know where you live but be aware that the fan won't come on at all until a sensor on the engine reaches a minimum temperature. If this wire is missing or the sensor is bad, the fan won't come on, period (and the engine won't run well either).

86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project
Reply With Quote


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 10:16 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page