I have an 87 300SDL and the blower was not working properly. I tracked it down to the 30amp fuse (just outside the fusebox) and replaced it and I had great AC for 2 days.

Yesterday - the AC stopped and all I get is HOT air out of the defrost. I noticed that the #5 fuse was blown and I replaced it with another white one. The blower and AC worked when the key was in ignition slot II but when I start the car - it blows the #5 fuse. I tried another new fuse with the same result.

Any help would be greatly appreciated. We finally have some warm weather - and I am getting roasted driving with the HOT air coming out (it doesn't matter what setting I have on the CCU).

What else is on the #5 fuze

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1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

number 5 fuse controls your ccu, aspirator blower motor,aux coolant pump,switchover valve for the climate control,A/C compressor control unit,starter lockout and backup light switch,aux fan pre resistor relay.

If I was a betting man, I would pick the aux coolant pump first. i bet it is seized.Unplug it, put in a new fuse and try it again.

John

The reason that the air is coming out the defrost only when the fuse blow is because that is the default setting for the CCU

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John
1986 300sdl
1985 380se

2nd choice would be Auxiliary Fan Resistor (Not the Relay) [could be the same
cause,the resistor will abuse the relay if non-fused or if the fuse can't act
quickly enough]they are known to melt.

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'84 300SD sold
124.128

Put the CCU on the low speed fan setting, replace the fuse, start the engine and report back if it blows the fuse.

Yes - with the CCU on low - the #5 fuse still blows right after starting the car. I haven't tried unplugging the pump yet - that will be my next step.

Thanks for the suggestions!