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  #1  
Old 06-30-2003, 03:57 PM
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86SDL A/C Question

I had the 86 SDL A/C checked out since it has been working intermittantly. Mech says, High side 155, Low side 45 lbs. Temps 51 degrees @ idle. Says I need Push Button Unit. $350 !!

Since he's getting pressure and temps, he had to jump something (compressor) to get these readings. Question is, what to jump and how ???? It appears that he made a slit on a blue/green 16 guage wire running next to the fuel filter coming up from the Compressor and dissapearing into the firewall.

Is this the +12 ? Wish I had a wiring diagram to make sure. I don't want to fry anything. I would just like to verify it's the PB unit before spending the $350 bucks + $125 to put it in.

I searched but never found anything difinitive.
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  #2  
Old 06-30-2003, 03:58 PM
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Look

Take a look on ebay - you can find these for $100
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  #3  
Old 06-30-2003, 05:06 PM
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What's working intermittently? Blower control? Compressor control? Register control? If the compressor seems to take a nap now and then it's probably a bad input to the Klima relay or a bad Klima relay. Don't start throwing money at this problem because there's a lot you can throw at it without fixing anything.

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  #4  
Old 06-30-2003, 08:53 PM
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It's the Compressor that's was intermittant. Not kicking in at all. Now it never kicks in. All blowers and flaps work correctly and heater works like it suppose to.

So I would like to know how to jump the compressor or Kilma or both to make sure it's the Push Button or Temp Selector Dial that's causing the problems.

The Mech got the compressor to work, and temp to drop, as I described in my first post, so that seems to eliminate a bunch of stuff. We know the compressor works fine. Freon level and pressure is o.k.
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  #5  
Old 07-01-2003, 12:22 AM
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The first thing to check are the connectors on the pressure switches on the dryer behind the left headlight. I assume your tech checked these connectors but if he didn't suspect the Klima relay and jumped on the ACC control unit, I don't expect he would have checked these connectors. It might just be a matter of making a good connection.

No go? Look for the 105C/115C switch at the front of the engine. Follow the upper radiator hose to where it meets the engine. In what looks like a thermostat housing (the thermostat is at the engine end of the lower radiator hose) there'll be something that looks like a temp sensor with two electrical connectors on it. TEMPORARILY disconnect the electrical connectors and see if that gets your compressor going. The plastic connector casings will probably disintegrate in your grip but such is life.

If that gets your compressor going, yours will be the third SDL with a bad 105C/115C I hear of this summer. The switch isn't expensive in the grand scheme of AC things.

If that doesn't do it, get your hands on a relay. Any relay but I know the black cubic inch ones like a Bosch 30A relay will work for sure. Get at least an 8A relay to be safe since that's the rating of the fuse on the circuit we're dealing with. Get some spade connectors or whatever the relay takes and some bullet connectors that you can get at Radioshack. Wire one end of the coil and one end of the switch to the first bullet connector. Wire the other end of the switch to the second bullet connector. Wire the other then of the coil to the third bullet connector.

Remove the Klima relay and consider that the socket left behind has two rows of 6 ports. Connect the relay to the socket in the following manner:

0-0-1-2-0-0
0-0-0-X-3-0

Where 0 = empty ports, 1 = the first bullet connector, 2 = the second bullet connector, 3 = the third bullet connector, X = the blocked port.

The first port provides +12V to one end of the coil and one end of the switch. The second port connects to the compressor. The third port provides a ground to the coil when the AC control unit wants the compressor to engage.

You might use something like an ice pick to spread the bullet connectors for a snug fit in the ports.

Hopefully this will get the compressor to work. I'm 99+% sure it will work since the AC controller is not often the reason that the compressor doesn't engage based on my unscientific statistics.

NOTE THAT THIS DISABLES A NUMBER OF PROTECTIVE INTERRUPTS. The compressor will not disengage when the coolant temp is at or over 115C, the compressor will not disengage when the compressor rpm doesn't match engine rpm, the compressor will not disengage at WOT, and the Klima relay will not send whatever signal it sends to the AT kickdown switch. In short, this is a diagnostic tool to allow you to test the inputs to the Klima relay.

Maybe your tech has the tools to do this in a more scientific way but when you mentioned that he spliced into the compressor wiring, I got the sense he's a jack-of-all-trades-master-of-none sort.

BTW, there are other things to consider such as checking the solder joints in the Klima relay but that's beyond the scope of things I know or have read.

Sixto
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  #6  
Old 07-01-2003, 11:28 AM
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I've pulled the 105/115 no go and checked the pressure switch still no go.

Just happen to have a Bosche 20/30A relay with a socket and wires coming out of it.

The terminals are: 85-one sideof coil,
86 other side of coil,
30, one side of switch Usually +12
87 other side of the switch norm. open.
87a switch norm.closed-rest postition
So if I understand you,

#1. wire 85 to 87 together put a bullet on it.
#2. Put a bullet on 86.
#3. Put a bullet on 30

I just need to be clear on what terminals on the Bosche relay go to the appropriate socket recepticles in your diagram i.e., 1,2,3.

Keep it coming I think we'll make progress here.
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  #7  
Old 07-01-2003, 11:48 AM
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A point of clarification. Instead of just checking the connections of the pressure switches at the dryer, jump the wires. One pair should get the auxiliary fan going, the other should complete the circuit from the AC control unit to the Klima relay.

Also, I didn't mention the WOT switch. Look for a contact swtich along the throttle linkage behind the IP. There's a small plastic case that looks out of place among the neighboring components. There'll be an electrical connector fitting into it from below. Pull that connector and see what happens.

Using this as a reference:

http://www.classictruckshop.com/clubs/earlyburbs/projects/bosch/relay.htm

30 and 85 are joined to the first bullet, 87 goes to the second bullet and 86 goes to the third bullet.

If the relay makes it work, then the problem could be with the engine rpm input or the compressor rpm input. I don't know how to test those feeds. Maybe with a scope but that's way beyond me.

Of course there's always the original possibility that the AC control unit is bad. You can check that the third bullet connector provides a ground signal to the Klima relay when the compressor should be engaged.

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  #8  
Old 07-01-2003, 01:30 PM
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Ok here's results.

Put the Bosh relay in. At first nothing. Go fool with A/C buttons. Wham ! Compressor kicks in.

Go back and press fan buttons. Auto to low to high. Still o.k. Move temp wheel. Can hear the fan slow down when I roll the temp wheel to white/red zone - seems normal and o.k.

Now, push buttons from A/C to Economy and back. Compressor cuts out. Fool with the buttons, press A/C button in hard a few times. Get compressor going again. Cabin temps drop.

Don't touch buttons, cut engine, put back Klima relay. Compressor still running o.k. and cooling. Not touching buttons anymore.

What do you think ?? Buttons ?? Inconclusive ? Klima relay o.k. ?
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  #9  
Old 07-01-2003, 03:48 PM
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That's how it works with me. The Klima relay works up to a point then refuses to engage the compressor under any circumstance. I swap in the simple relay and it works continuously. Swap back the Klima relay and it works for a finite amount of time.

The fact that the simple relay works all the time tells me that the there's nothing wrong upstream of the Klima relay. If so, I'm left with things I can't test like the Klima relay, engine rpm input and compressor rpm input.

Someone I'm corresponding with keeps blowing a solder joint in his Klima relay. It could be that something's getting hot and quitting inside the Klima relay. Is there a circuit breaker function in the Klima relay? Electronics is beyond my scope of knowledge.

Misery might love company but it's still misery.

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  #10  
Old 07-01-2003, 04:25 PM
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I agree with your situation. It if works all of the time with the test relay, then its got to be the Klima. Simple. How long do you think the test relay can be left in ?

1. Mine will NOT to work consistantly with the Simple relay. Had to fool with the A/C button to get the comp to work.
2. Put the Klima back in, works again, but still have to fiddle with the A/C button.

I know this doesn't mean the Klima is good but, I'm leaning towards the buttons on mine.

I'm going to drive it, and not touch buttons for a long time and see if it cuts out. This may be indicative of a time vs. hot temp Kilma thing. Of course vibration could jar the buttons or the relay and I'll be back where I started from.

Klima is silicone sealed. I can't get into it. A schematic would be nice, to find a circuit breaker if one exists. But, you'd think a fuse would blow first.
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  #11  
Old 07-01-2003, 05:00 PM
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You might just have a bad cabin temp sensor or evaporator temp sensor.

These are the test specs for the cabin temp sensor:

15C = 15.7kO +/- .5kO
25C = 10kO +/- .5kO
35C = 6.5kO +/- .5kO

I can't find specs for the evaporator temp sensor. It might suffice to disconnect it if you know where it is. I don't.

It's easy to scrape off the silicone to get to the innards of the Klima relay. You don't even have to scrape it. Just get a blade between the floor and the case and pry.

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  #12  
Old 07-02-2003, 11:30 AM
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O.K., I'll test anything I can get to at this point.

I think my cabin temp sensor is above the little center visor. How do I test it ? Can I get a meter in there somehow ?

Could you tell me where the evap. temp sensor is ? What are the readings suppose to be ? Or just jump it ?

One more question. What is suppose to trigger the AUX radiator fan ? Can I jump it to check it somehow ? Is it suppose to trigger with the Compressor ?
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  #13  
Old 07-02-2003, 12:33 PM
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PB Unit

BTW, if you want a relatively inexpensive source for a remanufactured push-button unit, I got mine for the 1983 300SD from george_murphy@compuserve.com. The 15 year original gave out in 1998 and I now have five years on the reman (core replacement deposit also required) which is notable for its correct function and far faster response. Plus the buttons are nice and new and no longer fall out!

George charges $149/$159 (I suspect the latter is for the later W126 cars like your SDL) which is only $50 more than the $100 for the one from the wrecker of unknown provenance.

Hopefully, it's something simpler/cheaper than that, but I would recommend George as a person of high integrity. He's a great source for early W123/107 ACC units and for rebuilt cruise control amps - one of the latter graces the 300SD also, and one of his reman ACC units is in the wife's 380SLC.

Few know more about MB vehicles than George.
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  #14  
Old 07-02-2003, 12:58 PM
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The aux fan is suppost to be triggered by 2 switches. The temp switch on the reciever/dryer or the temp switch on the thermostat housing.
On the reciever/dryer the switch unit that sticks out horizontally is the temp unit. pull of the connectors and make a short wire with bayonnet connectors at each end to jump this. Or use a short wire if just checking it . Connect the 2 wires that lead to this switch. Your aux fan should come on when the car ignition is turned on.

Dave
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  #15  
Old 07-02-2003, 03:24 PM
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Quote:
Originally posted by alan911
What is suppose to trigger the AUX radiator fan ? Can I jump it to check it somehow ? Is it suppose to trigger with the Compressor ?
Look for the 105/115 switch at the engine end of the upper radiator hose. Pull the single connector and ground the wire. With the engine running, the aux fan should come on full tilt. It should come on at 105C. It'll come on partial tilt (through a resistor) with the receiver/dryer switch. At 115C, the compressor should cut out, but there's no connection between the aux fan and the compressor except that they share a temp switch housing.

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