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Old 05-29-2003, 03:32 AM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 18,746
Klima relay pin outs (87 SDL or any late 126)

Does anyone know what the pin outs are for a Klima relay for an 87 300SDL? The markings on the pin face go...

GK- GK+ 87 15 TD 31
T KL <gap> 87K VL GM+

The manual says there are connection for...

engine rpm
AC compressor power
compressor speed input 1
compressor speed input 2
ACC push button unit input
coolant temp input
WOT switch input
kick down switch input (86 SDL only)

I'd like to run some diagnostics because my compressor works fine when I start the car but at some seemingly random point it cuts out and won't come back on until the engine's been off for a few hours. Low and high side pressures check out when it's running. I can tear open the harness sheathing but it'll be more elegant to tap into the pins.

91 300SE
87 300SDL
83 300SD
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Old 05-29-2003, 08:24 AM
TX76513's Avatar
Platinum Member
Join Date: Apr 2003
Location: Brandon, Mississippi
Posts: 4,944
Just a thought

I fought this A/C nightmare (diagnosis) earlier this year - and my problem was exactly as you described. Check this first before you turn into a "jello head" like I did. There is a sensor on top/near the upper radiator hose - a dual pole and a single pole. Disconnect the single pole and see if this allows consistent cooling. My compressor side evidentaly was going bad (sometimes worked sometimes didn't) but the guage/light terminals worked fine. (Cheap part easy fix)
15 VW Passat TDI
97 S500
86 Holden Jackaroo Turbo D
86 300SDL
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Old 05-29-2003, 09:05 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
GK-/GK+ are compressor speed sensor in and out, 87 is the output to the clutch, 15 is the power from switched ignition, TD causes me problems it would be engine speed on a gas model but engine speed on this diesel is on GM+, 31 is ground, T is temp sensor, KL is the comp on signal from pushbutton controller, 87k is kickdown output, VL is full thjrottle switch, and GM+ is the engine speed as stated above.

The pin numbers are 1 to 12 with #1 being terminal 31 or the right top end of your list. Pin #2 is GM+. So left to right the numbers are
11, 9, 7, 5, 3, 1
12, 10, 8, 6, 4, 2,

The common problem with the system in general is the belt slipping triggering the speed sensing relationship. On diesels there seems to be quite a few problems with the engine speed signal. This signal is prepared by the EGR module if I recall. It takes the crankshaft induced AC signal and makes a DC pulse that is used by the tach and other users. The full throttle switch also cuts the compressor and does fail. Unplugging it bypasses that problem.

For some scope patterns and general diagnostics see this article:
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 05-29-2003, 10:11 AM
Registered User
Join Date: Jun 2000
Location: Plano, TX
Posts: 2,476
Sixto - I fought this problem on my 124 a few years ago - the compressor would drop out. Restarting the car would get it going again, sometimes for only a few seconds.

It turned out to be a multiple point problem. In my case it turned out to be a defective Klima relay, excessive compressor clutch gap, and grease/oil/gunk on the clutch facing. All these together conspired to trigger the compressor speed sensor cutout.

You're going down the right path in analyzing and understanding the input signals to the Klima relay. A few thoughts on this - the signal from the PBU is ground, not +12v. If your tach works consistently, then it's very unlikely you have an issue with the engine speed signal. You can test the compressor by jumpering 15 to 87. I built a Klima replacement from a standard "ice-cube" relay. It used the ground signal from KL to switch on (power was provided by 15). When switch on, 15 provided power to 87. If the a/c works consistently with this replacement setup, you can eliminate the PBU and compressor clutch coil as possible problem sources. I don't recommend leaving this alternative in place - you lose the protection of the serpentine belt by the speed sensor mechanism. It can be a useful diagnostic tool for the do-it-yerselfer, though.

- JimY
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Old 05-29-2003, 01:15 PM
HL3 HL3 is offline
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Join Date: May 2003
Location: ROCKLIN, CA
Posts: 19
Question "Ice Cube Relay"


I didn't understand your referrence to "ice cube"...And pls a little more detail on how to make....sounds like it could be a very important diagnoisic tool for ACC problems...Thanks

86 300E
99 E320
97 Dodge Durango SLT 5.2 V8
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Old 05-29-2003, 06:40 PM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 18,746
Thanks for the great responses.

A couple of follow up questions

- Why does the diagram show that the kickdown switch connection to be an output instead of an input?

- The flakiness might have started after I changed the main fuel filter and spilled some fuel on the clutch. What can I use to clean the clutch surfaces? Is brake parts cleaner safe?

91 300SE
87 300SDL
83 300SD
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Old 05-30-2003, 10:32 AM
Registered User
Join Date: Jun 2000
Location: Plano, TX
Posts: 2,476
An ice cube relay is a simple single pole double throw relay used all over MB cars. There's a bunch of them in the relay comparment of the fuse box. It's so called because they are about 1 inch square and made of bright silver metal - they do look like an ice cube.

I don't have a wiring diagram handy, and I'd be a bit reluctant to post it if I did. Here's why. As SteveB points out in another related thread, some cars use a ground signal to indicate compressor on, others use +12v. You need to determine which your car uses and wire up the bypass appropriately. It's a simple task which requires only a DVM. However, if all this is beyond you, then you're probably best off not going there.

Sixto - I noticed that while I had the bypass in place that kickdowns did not work, at least not all the time. I think the full throttle signal causes the Klima relay to both disable the compressor and signal for a kickdown. It's certainly something you can live without, but is nice to have.

Brake parts cleaner shoud work just fine. Just saturate the clutch air gap. I think I used Simple Green followed by a good hosing down. Either should do the job.

- JimY
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