[W126 Coupe] 1985 500 SeC

[Dick Spellman]

Rick:

As has been suggested, check to see that the mono valve plunger is 
working properly.  If not replace it with the repair kit (under $30 US) 
and 10 minutes work.  Two other possibilities are 1: a bad ignition 
switch (test this by trying repeated starts, each time waiting to see if 
the heater works properly.  If it's intermittent then the ignition 
switch may well be the problem.  2. is a bad vacuum switch over valve or 
the related vacuum elements that determine where air is to be 
delivered.  This will not influence the heating of the air only the 
local delivery vents being used.  There is an output test in the MB 
manual that must be followed to confirm correct operation or you can 
just test each element at the vacuum switch-over valve using a Mighty 
Vac pulling 12-15hg no more per line.

Post back with the mono-valve status and we can go from there on the 
other topics in greater detail.

Answer to your question, there is a blower fuse (either works or does 
not) yours is working, there is the ACC fuse on the 85 which is fuse # 
10 (rated 8 amps-color is white), there is a fuse for the blower motor 
and AC switchover relay which is fuse #11 (rated 25 amps-color is 
blue)-NOTE this should have been removed from the fuse box and 
re-installed as a separate foil fuse holder out on the fire wall by the 
brake booster vacuum line as a fix by MB to stop over-heating fuse 
terminals in the fuse box.

You're operating the system with Auto selected, EC selected and temp 
dial at MAX?  Coolant temp on engine is a normal 80-85 C when warmed 
up?  This temp stays fairly stable at idle and at speed?

Dick
reference: <http://www.mbcoupes.com/repairarticles/fuse/85500eurofuses.htm>

WRick11499 at aol.com wrote:

> Its cold here in MD. and my heater is acting crazy. Some times works 

> and sometimes not.I bought a rebuilt  climite control unit and it does 

> the same thing.Some times the defroster blows hot and the center vents 

> blows cold and sometimes every thing works alright but most of the 

> time   all blow cold.The  small pump on the firewall seems to be 

> working plus I bought a newOverload relay.If I disconect  a battery 

> cable and then replace it, itseems to be O.K. till I turn the key off, 

> so I think it must be electrical, are there other relays that I should 

> check and where are they located in the fuse box, has anyone else had 

> a problem like this.Thanks for any help    Rick 

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