electrical problems on 1984 300td

[co.aulakh]

three problems i have.
1.the light on the air condition switching panel comes on sometimes and does not at other times.this light is supposed to be on at ALL times when engine is started.i cannot find any relay etc.
2.the tachometer also stops working suddenly at times: will come on again sometimes only when i play with the air conditioner switches.
3.the automatic temperature control does not maintain the temperature steadily.sometimes on a long run it seems to work ok ;at other times i have the guage at 26 degrees and outsid temperature is zero and it will start blowing cold air.the only way,then ,to get hot air is to put the knob on maximum.
any help will be appreciated.
thanks

[stevebfl]

#1 - The illumination lighting has no connection to the A/C circuitry. From the wiring diagram the power comes from a junction C124 located in the RH drivers footwell. The junction gets its power from the dimmer reostat. Do your lights go up and down the same with the reostat?

#2 - That year Turbodiesel has no conection between tach function and A/C operation. I think a separate problem here.

#3 - The "Min" position turns off the heater valve no matter what the temp. "Max" turns it on totally. In between the valve is pulsed. The control is from a separate controller behind the glove box on the side of the evaporator housing. You will need a wiring diagram if you wish to check it.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

[co.aulakh]

thanks ,steve.
1.i will check the rh footwell connections.
2.actually when the tach stops working ;and if i blow the horn it comes into life again!!!i just found that out today.
3the minimum and max work fine.its the pulsed signals that do not work so good....any ideas what to look for???
regards