Can anyone tell me where the second fuse (strip fuse?) is in my 87 300E? I've read it's just in front of the main fuse box, but I can't find it...
Thanks.

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Ty H.
'87 300E 135K Miles

There probably isn't one. The added strip fuse was installed on later models in production due to early failings. It is also often added where the fuse contacts have fried in the box. If it isn't around the shock tower or near the master cylinder compartment then you probably don't have one.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Is it mounted on the strut tower, fairly heavy gauge wires on both ends, with a small, thin metal (i.e. strip fuse?) between them? If so, it was right in front of my face, just didn't realize what it was...

I have made some progress (hopefully I didn't do too many things at once leaving me unsure of the problem...) I cleaned and replaced the #7 and 10 fuses--they both seemed fine. I also rotated the relays (they're all silver Hella fuses--indication they're all replacements?) just to see if that made any difference...

With the car at running temp (i.e. 80c), I jumped the 105/115 switch and the FAN CAME ON (yipee!) at high speed. Then I jumped the AC switch w/ the ac running and engine temp somewhere between 80 and 100 and the fan came on at low speed. So, it looks like the ballast resister is ok since it ran on low speed...

With that, it looks like I need a new AC switch. I'm not so sure about the 105/115 switch. I'm not certain the engine got up to 105 just sitting in the driveway running (it did rise above 80 but I wouldn't say it was half way to 100). The only thing that confuses me, is yesterday when I was running it around lunch time, the engine temp was above the 100 mark and the fan still didn't turn on... That would make me think the 105/115 switch is bad too. Seems unlikely that both would go bad at same time though... I need to get it up to temp today (over the 100 mark) after messing w/ fuses and relays and see if it kicks on. If not, it would appear both switches are bad? Am I thinking clearly here?

BTW, this forum is fantastic--I know enough just to get myself in trouble, but w/ all the info on this board, I might be able to actually figure it out--with out having to run wires and a toggle switch up to the dash to turn it on manually (not at all becoming of a MB ).

Thanks in advance.

__________________
Ty H.
'87 300E 135K Miles

You have verified the low and high fan circuits w/jumpering the sensors/switches.. . Now you need to know if the 105 trips at temp for high fan.
But, on low fan you have verified the circuit by jumpimg the a/c pressure sw,. but do not assume that sw to be bad. It has to see a high pressure from the a/c system before it trips and many do not trip b/c the system is slighly low on refrigerant [ meaning high side never gets to trip pressure] . Gauges are needed here , or you can monitor the refrigerant eye sight. [ if yu still have the original R12]. Also be aware that the high side of a fully charged system will not get to sw trigger pressure if the ambient temps are low. The aux fan is just that---an aux air-flow when either the coolant gets out of line or the a/c sees a high thermal load...they both work when either system is being taxed ..they do not work until these conditions are met.

The strip you see may be the heater blower fuse...which would have nothing to do w.aux fan circuits.

Does the refrigerant eyesight look different at high or lower pressures?

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1992 400E current
1988 300E sold
1973 280C totalled
1973 280SEL never got it running
1971 250C my first love but rusted out

Low refrig would be indicated by foam/bubbles.full charge would be clear ..
That is if the unit was not converted to R134...many were. R134 will show some bubbles even when fully charged,,that's why you would need gauges and sw pressure cut-in spec to make that sw diagnosis if R134.

Usually you can get the high pressure sw to trigger if you try the a/c at a high idle on a hot day. Can even block the radiator a little to getthngs up there. Just use your head.

On you coment of a manual toggle in the cabin..this is an excellent idea used by many on the older Benzs..you put a toggle in the cabin wired across the a/c pressure sw. that it gives you control of low fan anytime you see the temps creeping up..this is excellent in traffic or towing, etc...the niceity of it is that it does not interfer with the stock system, but lets you over-ride the sensors to get a jump on it...best of both worlds..I have used one on all my Benzs over many years and they are just a nice saftey feature to have when that one time comes into being..like stuck in traffic at the Beach, ya know??????
The newer units have fan default if a sensor goes, so they do not need it, but the older units don't , so you just add this and you are in control..

Refrigerant is a colorless gas or liquid depending on temp or pressure. The sight glass will appear clear when the system is empty or when it full. When it is part full the liquid is foamed by the turbulence of flow with gaseous refrigerant. This will look milky.

To really get an idea of what you are looking at, have someone inside the car shut off the AC compressor while you watch. Even a clear/full system will slow down and show some foam and then the liquid surface level will appear and recede. The only true way to know the state of charge is by weighing in the proper amount. Arthur is sure right about that fan not coming on if the pressures are low.

I get a few cars every year that start to run hot because the AC has lost enough refrigerant that the fan stops coming on and the cooling system gets noticably hotter as a result.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

by the way, I wish I had the problem of being stuck in traffic at the beach...!

Believe me, It is not all it is cracked up to be. In my 88 300E w 91K miles, no air conditioning (yet) and the temp gauge creeping past 100, it can be very aggravating! I think I may install a toggle switch some where on the dash.

__________________
1992 400E current
1988 300E sold
1973 280C totalled
1973 280SEL never got it running
1971 250C my first love but rusted out