compressor - tach connection - PeachParts Mercedes-Benz Forum

jmann.arch · #1 05-23-2010, 05:06 PM

I have been gradually fixing an A/C/blower issue on a car that sat for a few months. Yesterday I fixed the blower motor by replacing the regulator. I thought I might need to add some refrigerant/oil to get the compressor to kick on because it didn't. I picked up some R134 w the oil and went to charge the system - but the valve that came with the can said the pressure was fine - so it appears I really don't have a leak.

I had noticed recently that my tachometer had stopped working (before I got the blower fixed) - and had read on some of the posts about the tach indicating engine speed let the compressor know when to come on.

Is there a test for the overload protection relay?

I took out the compressor control module - mine is labeled D-KLI/KD - I assume this is the Klima? I tried jumping pin socket 5 to 7 on the socket in the hopes that the compressor would come on to no avail.

Is there a way to definately tell that the tach issue is connected to the compressor not starting? I have not found anything in the cd manual that helps out with this one.

Jimmy

biopete · #2 05-23-2010, 11:34 PM

Jmann. I see u in tn. Me too. Nville. Is your ovp red? Same as 87 td? If so I have one u can borrow to try.

Jeremy5848 · #3 05-24-2010, 12:42 AM

One of the KLima inputs is the tach signal -- it keeps the compressor from engaging when the engine has just started and isn't up to at least 600 RPM. No tach signal, no compressor.

The most likely cause of the tach problem is the OVP relay or its built-in fuse. The OVP relay is located behind the battery near the Klima relay.

Jeremy

jmann.arch · #4 05-24-2010, 06:11 AM

I have pulled both the Klima and the OVP out to take a look. The OVP had a 10a fuse in the top which looked fine - but I assume you are speaking of an internal fuse.

Is there any reason to suspect a problem with the Klima relay?

jmann.arch · #5 05-24-2010, 06:17 AM

Biopete - I appreciate the offer. I think I am just going to order an OVP. I have gotten pretty used to the drill of ordering a couple of parts when a test is inconclusive and returning the one I don't need. Thanks!

jmann.arch · #6 05-24-2010, 06:22 AM

Jeremy -

If the OVP relay has a built in fuse then is there a way to jump that circuit to check and see if the tach works again? I didn't see anything diagramming the pins on the ovp relay.

Jimmy

jmann.arch · #7 05-26-2010, 11:11 PM

Okay - well the new OVP and Klima came in - I tried them - no change - so the tach issue was not an overload as seemed to make sense with the blower and other stuff I changed out.

So I got disappointed and then I put the car up on jack stands and searched around for the tach after pulling up the tach check DIY post from filon102. I removed the inductance transmitter and tested it with the screwdriver to see if there was any signal - and no luck. I got ready to put it back on and that's when I saw this. (attached pic)

I don't know what caused this but the wire from the inductance transmitter has two big gashes in it - one nearly through it. I don't see anything that could have caused this - and have no idea why an animal might gnaw on it - but either way this is my tach issue - so a new inductance transmitter/harness has been ordered.

Is it easy to get to all the connections on this thing?

With luck we'll have cool air by Saturday morning.

Jeremy5848 · #8 05-27-2010, 12:43 AM

I would think (hope) that the connectors would be placed where you can get at them -- Mercedes is usually pretty good about that. As for critters chewing on wiring, my next-door neighbor lost a nice car due to rats eating enough of four wiring harnesses that replacement was required. The cost of the labor to go through almost the entire car was so much that the owner ended up scrapping the car. So it can happen. It's also possible, if your car lacks its belly panels, to have hit something that took a chunk out of the cable.

jmann.arch · #9 05-31-2010, 02:14 AM

Well - I replaced the tach sensor. The sensor is on the transmission and the wire snakes around to the back firewall, pokes thru in front of the blower motor and runs over to a connection next to the battery. I had to take off all the stuff to get to the blower motor again - but am gettting really used to it!

Unfortunately - although I have the tachometer working agin - I do not have A/C - so either the compressor clutch is bad (I need to test), or some other input the klima is getting. Is it easy to get to the power connectors for the clutch?

Is there any way to test the full-throttle switch or dual-pressure switch?

I had ordered a new klima relay, and a OVP relay before figuring out it was simply the tach sensor.