This “fix” will apply to ALL earlier Mercedes vehicles that utilize the old style “bullet” type plastic fuses...I just happened to be troubleshooting my W201 1987 190D Turbo...

I have had this problem before with this car- sometimes the AC compressor would turn on and sometimes it wouldn’t. Then it would run for a while and then shut off. Sometimes the blower fan would work fine, and then suddenly completely shut down. This time I started having other gremlins as well- the push button controller stopped directing the vents; the front overhead dome started turning on and off by itself and the vacuum pump for the power locks stopped working. These all are some very common complaints I regularly see posted on this and other Mercedes oriented forums.

I was primarily concerned with the AC since it was 90 degrees outside...there are many threads on this website with people chasing the same gremlins. Possible fixes could be low freon, bad speed switch on the compressor, bad temp sensor on the Receiver dryer, bad push button controller, bad changeover valve...etc, etc...

Pondering all the things I’d need to check with with my multimeter, I decided to keep it simple first. The lowest hanging fruit was the fuse box. I checked all the fuses and none appeared blown and all looked fine. I wiggled and rotated the compressor fuse, then tried the AC and it still did not work. The fuse contacts did not appear to have any corrosion, but I decided to go all-in at this point.

I removed all the fuses one by one and closely examined them. No apparent cracks but strangely, one end of the compressor fuse the metal was slightly discolored- kind of how an exhaust system shows “blueing” and discoloration from heat cycling. I then removed them all (they were the old aluminum contact style) There was just a little evidence of aluminum corrosion “dust” under a number of the fuses in the case. Next I used a fine brass brush and electrical contact cleaner and carefully scrubbed all the contact points in the fuse box. I bought a new supply of copper contact fuses and reinstalled every single new fuse with a dab of Dielectric grease on each end.

The next phase was pure glory- I started the car up and the AC compressor fired right up! I checked the Freon pressure and saw it was at the bottom of the “ok” range so I charged it up and now the air was ice cold. Next I checked all my other gremlins and they ALL had been fixed! The push button controller, the cabin fan, the power locks, the overhead dome light- they all now worked perfectly. I then took the car out for an hour long drive and everything functioned perfectly.

My take from all this is BEFORE you pull out your multimeter: swap fuses and clean the contacts. If that fuse is not making good contact, the multimeter may tell you that there is something wrong with the circuit, but it may also point you in the wrong direction if it is just a fuse contact problem to begin with. Also, I have seen people saying their fuse/fuse boxes are getting abnormally hot. This is ALSO an indicator of a poor electrical connection. If there is just a small amount of corrosion at the end of a fuse, it will cause resistance and it will heat that fuse up while not necessarily “blowing” the fuse outright. It may show as just blueing of the aluminum fuse wire slightly as mine did. The electrical components in these cars each call for very specific volts and amps- a very small amount of corrosion at the fuse box will cause them to malfunction in very strange ways sometimes.

Good luck!

J.G.

Thanks for a reminder. This has been a common problem, and I've known about it.

Just yesterday I was driving around shopping. Last stop coming home, no AC when I got in car. Went thru everything in my mind, always fearing the worst, a leak or a bad Klima. AC just didn't work yesterday. This AM had to run to the store and AC worked perfectly. I'm certain it's the corrosion on the fuses, which I'm about to clean after I post this. Hadn't done it in about 4 years. Thanks again for a good reminder!

I did the same...been years since I touched the fuse box or had a problem. I had the compressor drop out first, then the fan a few days later. Then the dome light and vacuum pump. Just seemed strange that a bunch of problems cropped up so quickly and figured best to rule out the most simple and potentially “common” points. What more simple and common point than the fuse box??!! I also switched to the copper fuses. Most that were in the box were still aluminum ones which corrode much more easily.

Good luck!

J.G.

Be aware that there are two fuse boxes on this car, be sure you get all of them. The second box is just forward of the first, it has a plain black cover. It holds the fuses for the high speed fan circuit and the alarm system.

Yup...got that box too! I found out its a lot easier to get the main fuse box lid off and out if you remove that plain black covered box right in front of it first (Just two fuses and a relay in that small box...)

J.G.

This is a good reminder.

I replaced most of my fuses with copper ones a few years ago when I got the car but I was missing a few 8 amp white ones so I didn't replace all of them.

I don't have any electrical problems in my car but still today I decided to order the remaining copper Bussmann fuses.

Thanks

The relay in that box controls the fan for high speed. It has an integral fuse...when the fuse goes, the relay needs to be replaced. As you've discovered, fuses tend to degrade. i've actually had that relay melt down due to a faulty fuse. What you want to do is replace it with the updated relay that has a separate ATO fuse in the top.

Here's a close up look at one of the fuses...aluminium strip is very discoloured/tarnished and the plastic fuse itself is degraded...

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Plastic fuses never bring joy. Stick with ceramic, if you can find them.

Well it's been about a week and a half since my above referenced "fix" and a couple hundred more miles on the odometer. Everything still working perfectly so I'm going to officially call this as problem solved. I got concerned on a couple mornings when the compressor didn't seem to engage for a little over a minute and a half after startup. I timed it out on several subsequent days and found the delay happened each time I did a cold start, and each day was nearly exactly the same elapsed time at about 1 minute 40 seconds each time. I'm guessing it is a temp sensor that inhibits compressor engagement until the engine reaches a certain operating temperature.

Thanks to all for the help, and I hope my results have been of help to someone else with the same problems.

J.G.