Testing ice cube relays
 

I found someone who will test all my ice cube relays (85 w201) for defects, which would be a big help in trying to debug my cruise and climate control. Its my understanding that these, along with the OVP are more than just relays-- is that accurate?


I imagine I will need to supply them with a schematic of each one. Are there schematics for these available, and if so, where are they?

Thanks!

the schematic is stamped/printed right on the relay itself. points 86 and 87 are the coil and 30 and 87 are the contact bridge. The numbers of the points are also printed on the relay next to each pin leg.

nothing too special

Some relays have a diode across the coil so polarity will matter.( I don't have a diagram. )

If connected backwards the diode will burn but the relay will still function. The diode is to snub the inductive kick when turned off. Not so much of a problem on a car with minimal electronics , more of a problem with an electronic laden car.

[QUOTE=Zulfiqar;3420164]the schematic is stamped/printed right on the relay itself. points 86 and 87 are the coil and 30 and 87 are the contact bridge. The numbers of the points are also printed on the relay next to each pin leg.

nothing too special[/QUOTE

For those of us who are schematically challenged, its pretty special! But thats great news.

What's the big deal about testing relays?

Fan relays usually include an internal fuse. If you still have the original black relay, the fuse is not replaceable. It's a good idea to replace these relays with a newer relay with a fuse in the top.

Climate control is complicated...you will have a Klima relay that controls the compressor. Bench testing the Klima relay is beyond the capabilities of most automotive shops, because it requires speed feeds from the crank sensor and the compressor sensor. To simulate this, they would need two signal generators. It's easier and cheaper to swap for a known good relay. There are two relays for the fans, and another if you have an electrical fan clutch. There are additional relays buried inside the fan switch, and lots of other electronic and vacuum controls. What is the problem with your climate system?

Im electrically challenged. Lets start with that.

I'm not getting voltage to my kickdown switch, which I believe comes from a cube relay in a box after the fuse terminals. IIRC. So thats one question. I cant test that cube.

I also seem to have issues controlling the cabin temp-- the little fan works, the vacuum pods seem to work, and I wish I knew if whichever relay feeds into that system can be ruled out or not.

So yes, I could just start throwing new relays in, but since I ran into a guy who runs a lab that builds electronic devices for the military, and he offered to have his geeks test whatever I sent him, Im going to pull them all out this winter and send them over to him.

Costs me nothing, and amuses a box full of geeks-- whats not to like?

No power to your kickdown switch (this is a 190D, right?), this means you have a problem with the Klima relay. It's not one of the cubes. The Klima is located in a hidden compartment behind the battery. Remove the weatherstrip under the windshield, and pop off the plastic cover. The Klima will be an oblong box about 2.5"x3", and it's marked Klima. There are many different Klimas, you need to match by part number.

I assume you have a prblem adjusting temperature...probably stuck on full hot. This is a complicated problem, involving vacuum and electronics, but is most likely a vacuum problem. Start by reading this writeup:

Troubleshooting the Mercedes-Benz 190 Tempmatic ACC Climate Control System

A vacuum leak ANYWHERE can cause problems with the tempamatic...I usually begin by replacing al the rubber elbows in the engine compartment, and then ramp it up if necessary.

Thanks for the direction. My electrical skills are limited to cleaning contacts and thats on a good day. I know where the Klima relay is located and you can see that my options are limited to replacing it with a new one (129.00) or a used one (pointless since I have a used one already) and I was thrilled to find someone who offered to inspect these ancient electronic components and report back for free. Is there a schematic for the Klima because I dont remember it having any inscriptions on its side.

Re tempmatic: I have that link and actually sent the guy 5.00 bucks once-- its a great write up and worth the money. I replaced a lot of elbow behind the glovebox. Currently I have a temp wheel that responds to on/off signals but nothing in between. So we're testing things. I have control of my vacuum pods and the PO replaced the whole tempmatic unit with a used one, so Im looking farther afield. I might still have a bad air fan: I replaced the first one and was changing air when I started, but I havent actually seen the tube that goes from the visor to the fan. It could be missing.

You really can't bench test a Klima relay, because it's not a simple electromechanical relay. In addition to power and ground connections on the coil and contacts, there are feeds from the compressor speed sensor and crank position sensor. It will turn off the A/C if the two speed sensors don't agree. On a Diesel, it also controls power to the kickdown switch: it will depower the switch when the engine is over the redline. With all these inputs and outputs, and the complexity of square wave and sine wave input, it would be quite a challenge to rig up a test. Replace or swap with known good. Just make sure you replace it with the same part number, as Klima's have to be matched to the number of cylinders, fuel type, and the sensors. You can also open the case on yours and inspect the PC board...it's not unusual to find a burned trace, which can be repaired.

On the climate control, make sure you have vacuum coming into the five position switchover valve. If not, then you default to on/off mode.

This is a good survey of what's going on in there. Thanks for the info. I'll send the two klimas I have over to the geeks; they're testi night vision goggle or something-- lets see how smart they really are! Stay tuned.

Meanwhile Ill go into position five and check it out. Thanks!