i have a 91 350sdl that i have had for about a month.
the A/C blows ice cold but never goes on high speed. i have tried defrost, manual High, automatic.
i have checked the temperature sensor blower motor and it is running fine.
should i start at the control side and resolder all the joints or should i start at the fan end.
thanks for any help

I had a problem with my 350sd when I bought it but I cant remember if it was just high speed or all speeds.It ended up being the tombstone fuse,it was in a little coffin shaped plastic box near the master cylinder,maybe just inboard of it,it was a flat fuse that had a hairline crack thru the middle of it making contact just sometimes,replaced it and it cured my problem,Johnny

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85 300sd SOLD ,85 745i,95 740i,1972 Suburban,1938 International

Just double checked,its directly in front of master cylinder ,take off the black top and fuse is held by two phillips screws,I hope this is your problem

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85 300sd SOLD ,85 745i,95 740i,1972 Suburban,1938 International

no joy on that. i did find it and it was fine.
i also tried a continuity test, and replacing the wire as well.
no difference.

Ok, I hooked the fan directly to the battery and it blew on high.
Does that mean it is only the regulator porcupine module thing?

hi, i have a 87 300d had no fan at all, if you have 3 prong connector on firewall, ck to see if you have power coming into connector when fan speed is on high . if so, follow harness into blower box, ck red wire on blower motor, if has power ck blue wire coming out of motor, if it has power it goes into blower regulator, see if power comes out of regulator , if not probaly bad blower regulator, if so, could be bad ground on other side of 3 prong connector.
if no power coming out of 3 prong connector, ck blower switch in controls and start there , hope this helps

i am getting correct voltages from the control unit just not to the fan. i am going to replace the regulator and go from there.

thanks for your help.

Did the regulator cure the problem ?

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85 300sd SOLD ,85 745i,95 740i,1972 Suburban,1938 International

i havent gotten the part yet. i will post when i install it.
thanks for your interest.

I had the same problem last year and performed the same diagnostics that you have and ended up replacing the regulator. Was able to find one used on Ebay for about $35, it fits many different models. Pretty expensive new...

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2001 E320
1991 350SD 265,000 - SOLD
2000 VW Beetle 1.8Turbo - restored
1997 E320 - SOLD
1988 190E - SOLD
1969 Mustang - SOLD

i got it installed this morning and it blows on high just perfectly. thanks for all the tips.

Congrats on your not giving up,and thanks for posting the fix.Im sure you need that high speed out in phoenix,Johnny

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85 300sd SOLD ,85 745i,95 740i,1972 Suburban,1938 International