New strip fuse... no power to climate control - PeachParts Mercedes-Benz Forum

Benz Mondi · #1 06-06-2017, 03:06 PM

I'm working through my list of issues with my 1990 300SEL. She runs like a champ now, but it's hot out so time to work on the Climate Control...

I've already replaced the strip fuse with a brand new one and confirmed that it doesn't have any cracks and is solid with a volt/ohm meter. Also checked the leads at the bolts that hold down the strip fuse (Dremel wire brush + dielectric grease). My test for power at the climate control is whether the night lights come on. I have 3 units to work with. I tested bulbs (6) for all 3 units. When I turn the ignition to position 1 and turn the headlight knob to position 1, the little bulb for the ash tray comes on but nothing on the Clima unit. What else can I do to test and get it running?

Thanks,
AL

Diseasel300 · #2 06-06-2017, 03:29 PM

The 30A strip fuse is for the blower. The CCU gets its power from a couple of other sources. Check the rest of the fuses in the fusebox. If you have any that are the aluminum composition, replace them with brass. It isn't uncommon for the aluminum ones to develop cracks you can't see until you remove the fuse from the holder and they fall apart in your hand...

Benz Mondi · #3 06-06-2017, 03:57 PM

Quote:

Originally Posted by Diseasel300

The 30A strip fuse is for the blower. The CCU gets its power from a couple of other sources. Check the rest of the fuses in the fusebox. If you have any that are the aluminum composition, replace them with brass. It isn't uncommon for the aluminum ones to develop cracks you can't see until you remove the fuse from the holder and they fall apart in your hand...

Thanks for your reply.

Because it's cheap and easy to do, with every car I get, I replace all the fuses with a brand new copper and brass assortment. I'll double check again though. Where / what else?

Diseasel300 · #4 06-06-2017, 04:01 PM

Main power for the ACC should be coming from Fuse #5. This controls the ACC, the KLIMA relay, and the little aspirator blower behind the glovebox.

Turn the key to "run" and wait for the seatbelt buzzer to quit and listen for the aspirator blower behind the passenger-side dash vent. If the fuse is good and it is running, the ACC itself may be bad or you may have a loose plug on the back side of it.

Frank Reiner · #5 06-06-2017, 04:13 PM

BM:

Cold and cracked solder joints in the ACC are the bane of those units.

Benz Mondi · #6 06-06-2017, 04:37 PM

Yes I can hear the small cabin temp blower/aspirator spinning with each of the 3 so I guess all 3 could actually be broken. I'll try warming up the solder joints tip and get another unit. They're cheap and I can return what I don't need within 30 days for a credit toward something else (Pick N Pull).

I visually check both plugs and didn't see anything out of place.

tinypanzer · #7 06-06-2017, 05:24 PM

Quote:

Originally Posted by Benz Mondi

Yes I can hear the small cabin temp blower/aspirator spinning with each of the 3 so I guess all 3 could actually be broken. I'll try warming up the solder joints tip and get another unit. They're cheap and I can return what I don't need within 30 days for a credit toward something else (Pick N Pull).

I visually check both plugs and didn't see anything out of place.

I think you're on the right track. Just a heads up, dielectric grease isn't intended for how you used it. A lot of people mistakenly think it helps or enhances electrical connections, but in reality it does the exact opposite. That's because it's 'dielectric' which means that it's an insulator. So while that dab of grease may stave off oxidation of the connection, it's really not helping it if the grease is actually covering the contacts. You may actually be increasing your electrical resistance in that case. Its real purpose is to be used as a sort of sealant or lubricant in situations where there are rubber insulators, to keep air and moisture out of an already made connection. Slathering on the terminals beforehand is bad. Use Caig Deoxit or a similar contact enhancer for that task, but don't use dielectric grease.

Benz Mondi · #8 06-06-2017, 07:31 PM

Quote:

Originally Posted by tinypanzer

I think you're on the right track. Just a heads up, dielectric grease isn't intended for how you used it. A lot of people mistakenly think it helps or enhances electrical connections, but in reality it does the exact opposite. That's because it's 'dielectric' which means that it's an insulator. So while that dab of grease may stave off oxidation of the connection, it's really not helping it if the grease is actually covering the contacts. You may actually be increasing your electrical resistance in that case. Its real purpose is to be used as a sort of sealant or lubricant in situations where there are rubber insulators, to keep air and moisture out of an already made connection. Slathering on the terminals beforehand is bad. Use Caig Deoxit or a similar contact enhancer for that task, but don't use dielectric grease.

Google seems to confirm what you've share. Geez all these years and only now I get the straight poop. I'll go back and clean up what I thought I was improving. Thanks.

tinypanzer · #9 06-06-2017, 09:04 PM

Quote:

Originally Posted by Benz Mondi

Google seems to confirm what you've share. Geez all these years and only now I get the straight poop. I'll go back and clean up what I thought I was improving. Thanks.

Don't feel bad. It's an EXTREMELY common misconception, made worse by how freely people repeat it to each other. I've seen it on this forum many times.

liquiddog · #10 06-06-2017, 11:39 PM

Not sure how similar to a 1990 190e your system is. But for me this was a bigger challenge than learning the CIS injection system.

Cutting out wiring harnesses from donor cars to bench test the switchover valves is what finally nailed it for me. My temp wheel works now and does work better than new cars I have been in. Especially in the winter.

Hit Man X · #11 06-07-2017, 12:13 AM

Your blower fan could me missing, disconnected, or have a dead resistor. Gen 2s use a PWM setup. Combine that with dead vacuum pods (very possible seeing how this car was driven into the ground), not a big shock you are receiving nothing from the fuse box.

1990 has the MAS relay, could be dying inside. BTDT.

Diseasel300 · #12 06-07-2017, 10:40 AM

Quote:

Originally Posted by tinypanzer

I think you're on the right track. Just a heads up, dielectric grease isn't intended for how you used it. A lot of people mistakenly think it helps or enhances electrical connections, but in reality it does the exact opposite. That's because it's 'dielectric' which means that it's an insulator. So while that dab of grease may stave off oxidation of the connection, it's really not helping it if the grease is actually covering the contacts. You may actually be increasing your electrical resistance in that case. Its real purpose is to be used as a sort of sealant or lubricant in situations where there are rubber insulators, to keep air and moisture out of an already made connection. Slathering on the terminals beforehand is bad. Use Caig Deoxit or a similar contact enhancer for that task, but don't use dielectric grease.

It depends on what KIND of dielectric grease you're using. There are specific types of "dielectric" greases made that are designed explicitly for electrical contacts, plugs, and switches. These types of dielectric grease are designed expressly to improve the electrical connection and will say so on the tube or can. They also tend to contain solvents and cleaners like the Caig DeOxit.

Plain old generic dielectric grease is typically used in sprinkler systems and other locations where the electrical connection is already made, but you want to make it weather-resistant. If you're buying a tube of dielectric grease, make sure it is the kind designed for electrical contacts, otherwise you're doing yourself a disservice.