450slc fan speed - PeachParts Mercedes-Benz Forum

kip Foss · #1 08-26-2003, 08:38 PM

I have a 1977 450slc. When I turn on the key or start the engine I can hear and feel the ac blower running very slowly. It is fast enough that I can feel air coming out of the vents. When I turn on the fan switch I have 4 fan speeds and all goes well. Is this normal that the fan should be on at a very low speed w/o the fan switch being on? I can't see any reason for it and can't see how I can get a fan speed lower than the lowest switch position. Any suggestions?

GermanMarque · #2 03-14-2005, 06:16 AM

I suppose late than never. Just had the same problem with my 280SL. On ignition on, fan can be heard and felt, despite being off on the switch. Still had it's four position fan speeds. Electrician had a look and found a green wire with a white trace connected to the air conditioner switch adjacent to the blower switch. This wire had no contact/connection with the fans black switch block and was piggy backed onto the air cond switch by a double male connector. Apparently Volvo fans run on start up and it appears it was a previous owner mod. The elctrician completed his trade in Sth Africa on Mercs, sp knpws them inside out. A little mad for his experience. Anyway disconnected the wire and no more fan problems. The green/white wire is hot, so was taped up. Everything else is working fine, so it's function is a mystery. It may not help, but it's one easy check to end the frustration.

hoddo · #3 03-15-2005, 05:02 AM

in my 79 450 slc the fan runs when in the 0 position also.. i dont think it a mod by previous owner .. fan works fine on all 4 speeds .. I always thought it was bcos these things are so darn airtight that it needed a permanant air supply for the pilot

GermanMarque · #4 03-16-2005, 02:30 AM

Dropped in to see my electrician and asked him your model specific. He's adamant it should not work on "0" that should be off. He said Volvo's were the only vehicle that had a constant fan on. Claimed your switch is obviously getting power with the ignition on, despite switch being on zero. You should have four speeds only. Said switch would not be the problem and that power is coming from another source. Test light and locate additional power source and eliminate it! He said it would not cause a problem leaving it on, just the annoyance of knowing it an't right. He said sounds like power is being bridged from another switch. He said from his experience, the krauts are fairly conservative with wiring and colour coding and nothing much has changed in colour coding with our vintage cars. Maybe find that green wire and see if it's lurking in amongst the wiring and vacume tubes and is the one causing you the grief.

UPSTATE NY · #5 03-25-2005, 05:55 PM

Kip, get an ohmeter and check the fan switch !

Later

280 SLick · #6 03-27-2005, 06:16 PM

I have a 1980 280 SL that I'm restoring. Though I'm new to the MB cars there are many standards in all makes. Manufacturers for years won't let you turn the ventilating fan off so you don't die in their product. The 280 SL solves this in a very unique way. The fan switch, when in the off positon, closes the vacum source for the the fresh air\recirculating servo. The result does not allow you to have both the fan off and the fresh air off at the same time where even minor amounts of CO loaded exhaust would be bad. The less complex and cheaper approach is just to leave the fan running low all the time (the time honored GM approach). You might want to rethink being able to turn the fan all the way off unless you are positive there is some sort of fresh air compensation.

Fitz2000 · #7 05-11-2005, 04:16 PM

I have a similar, but very different, issue with my 450SLC fan. I have only had my car for a short time so I am not too sure of what all the controls do. However, there is not too much to know about a five position switch (off and speeds 1 to 4). When switching on the ignition the fan has the four speeds you refer to. All speeds seem to work okay and the fan does not operate in the off position. However after the car has been running for a few miles the fan suddenly switches itself on to high power or top speed even though the switch is in the off position. I can not switch the fan off. The engine can be turned off, but until the car is cold you can not turn on the ignition without the fan blowing at top speed! Result I drive around with fan on in high power mode all the time. Very frustrating! Anyone got any ideas?

gerhuet · #8 05-13-2005, 05:04 AM

Quote:

Originally Posted by Fitz2000

I have a similar, but very different, issue with my 450SLC fan. I have only had my car for a short time so I am not too sure of what all the controls do. However, there is not too much to know about a five position switch (off and speeds 1 to 4). When switching on the ignition the fan has the four speeds you refer to. All speeds seem to work okay and the fan does not operate in the off position. However after the car has been running for a few miles the fan suddenly switches itself on to high power or top speed even though the switch is in the off position. I can not switch the fan off. The engine can be turned off, but until the car is cold you can not turn on the ignition without the fan blowing at top speed! Result I drive around with fan on in high power mode all the time. Very frustrating! Anyone got any ideas?

I have a '73 350 slc and have the exact same problem. As most of this series have erratic heater controls, it makes driving very uncomfortable. Fortunately in my part of the world we have quite a chilly climate, but if what passes for summer here it could become very unpleasent. Any ideas anyone ?

Gerry
Wexford, Ireland