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1988 300E a few questions

2K views 8 replies 5 participants last post by  augapfel 
#1 ·
i just bought a 1988 300e and i have a few questions/problems

1.i might have a wiring problem but how do the power locks work.
2. the heater works on defrost setting, however the other settings seem to be alot weaker airpressure. whats the problem.
3. it didn't come with a manual, can i buy one somewhere?

thanks for the help.
-zach
 
#2 ·
the power locks are vacuum activated. not electrical. there should be an electrical vacuum pump though.

the defrost setting uses the highest fan speed setting. look on the right hand side of the HVAC controls, there should be three buttons, one above the other. the top one is highest fan setting, the middle on is auto, the bottom on is lowest fan setting. most people leave the setting on auto, it will vary fan speed depending on what temperature youve selected and ambient temperature. if its 75 outside and youve got 75 selected, it wont blow very hard.

best check with a recycler to get a manual. mine didnt come with a manual either, but i used to be a mercedes mechanic so im familiar with all the controls.
 
#3 ·
1. The power locks work by either pushing down on the button at each door interior, or by turning the key in either front door or the trunk. Very standard behavior. Are they doing something unexpected?

2. See neanderthal, above.

3. You can get an Owner's Manual by calling 1-800-FOR-MERCEDES (1-800-367-6372). Mine cost, I think, about $12.50 plus shipping -- under twenty bucks, total. Very much worth the money.
 
#4 ·
it might be because i don't have a mercedes benz key. it is just one that was cut... not officially mercedes. i do turn the lock from the door but it doesn't lock the whole car thats why i thought it might be some kind od mechanical glitch.

regarding the heat: the only setting it works on is the defrost. the two vents up front don't work so i was wondering how much it would be to fix
 
#5 ·
If the key turns in the cylinder, then all the doors (+ trunk and gas flap) should lock and unlock together. So there's something wrong with the system.

Is it the same with all the locks, including the trunk? If so, then I'd start by looking for a single point of failure, such as the vacuum pump below the rear seat, driver's side. If not, then you've narrowed down the search.

You might want to pop on over to:

http://mb.braingears.com/124_DISC2/Program/central_locking.htm
http://mb.braingears.com/124_DISC1/Program/climate_manual.htm

for troubleshooting procedures for the locking system and the climate control.
 
#6 ·
hello neanderthal,

i do not have a manual either. what does the the "ec" button make happen on the climate control center. recirculate? also, i have noticed that my heater blows cold alot in the morning even though engine temp @ 80+ c. i can push some of the different buttons and it will start blowing warm most of the time and be fine all day. i tested the auxillary pump and checked the water valve. i have determined that my fault must lie with the climate control circuitry itself. do you agree??
 
#7 ·
EC is simply an abbreviation for economy and means that the a/c compressor does not run. Automatic fan speed and temp regulation continues but if outside temp is too high to privide cooling, well, then you get hot.

The heater should never blow cold unless you have the dial cranked way down to max blue. In fact, there's a switch that inhibits blower motor operation when it's cold outside until coolant temp reaches something like 100F. The selector button must be in full auto or econ auto for this to take place.
 
#9 ·
All I can tell you is that I've studied the wiring diagram pretty carefully and from what i can tell the climate control module (which is part of the control panel pushbutton assembly) gets info from a heater core temp sensor. This, i believe, is the device that tells the climate control module that it is time to turn on the blower motor (and do other stuff like influence the water valve pulse rate). It seems like the climate control module supplies voltage to the heater core temp sensor (as well as the outside temp sensor, the cabin temp sensor, and the evaporator temp sensor) on a brown/yellow strip wire and receives the heater core temp sensor signal on a gray/green stripe wire. I don't know what the resistance value/range is for the heater core temp sensor but typically an "open" resistor in a control system is perceived by a controller as a high temp signal. If this is the case a bad or disconnected heater core temp sensor would fool the climate control module into believeing that the heater core is always hot. I don't know where the heater core temp sensor is located but I bet it's hard to get at. :-(
 
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