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  #1  
Old 08-31-2014, 07:06 PM
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AC compressor won't come on- 85 300D

AC was working (but slowly getting warmer and warmer) since last topped up with R134 last summer. Compressor stopped kicking on today = no cooling. The temp dial is on max cold detent, the hi/lo pressure switch on receiver dryer is closed (1 ohm), fuses ok. From what I've read, 85 has a klima relay. Is it next to the blue flying saucer? I looked in FSM CD ACC III and was horrified to find an illegible wiring diagram- it is utterly useless! I have a degree in EE and electronics was a hobby and I tell you it is very frustrating w/o a wiring diagram. I searched but it seems a legible ACC III wiring diagram does not exist. If anyone has one, please post it. Thanks in advance!
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Old 08-31-2014, 07:50 PM
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Found a thread with great info on the Klima relay from Doktor Bert

Compressor Clutch Issue
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  #3  
Old 08-31-2014, 08:02 PM
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AC has a safety interlock

If there is no ac gas, the compressor will not turn on. Saves the compressor.
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  #4  
Old 09-01-2014, 04:05 PM
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Quote:
Originally Posted by rocky raccoon View Post
If there is no ac gas, the compressor will not turn on. Saves the compressor.
There is enough refrigerant such that the low pressure switch is closed, allowing the signals from the PBU and anti-ice switch to pass to the Klima relay.
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  #5  
Old 09-01-2014, 04:07 PM
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Found this excellent diagram from Jeremy and been trouble shooting from it. It does not have everything I need but it is better than anything in the FSM that I have. Per the diagram, which says the Klima relay is RPM controlled. Does anyone know where the RPM signal ties in? I have found no evidence of it so far in buzzing things out.

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Last edited by funola; 09-01-2014 at 04:21 PM.
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  #6  
Old 09-01-2014, 04:17 PM
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Took the Klima relay apart and have some pics. I re-flowed all solder joints which did not help. Also replaced a 47 uf electrolytic cap which did not help. There are 2 other 1 uf elec cap I did not replace (did not have) but they checked ok with an ohmmeter. I buzzed out most of the inputs to the Klima and they seem to to OK - micro switch top of valve cover, kick down switch, low pressure switch, PBU. I can push on compressor clutch relay and the clutch pulls in. At this point I am suspecting a defective Klima. Just bought a used Klima from Ebay- hope it's a good one. It would be difficult (not impossible) to fix the Klima w/o a schematic of the circuitry. I would not want to put the time into it.











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  #7  
Old 09-01-2014, 04:24 PM
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For the time being, while waiting for the used Klima to arrive, I made a jumper connecting pins 5 and 10 of the Klima relay socket which enables the compressor clutch and still allows the temp dial to control the compressor on/off.

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  #8  
Old 09-01-2014, 05:37 PM
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I am interested to see what you find. My Klima seems to be working intermittently. It will work for a few days then I'll find the compressor not kicking in. I can slightly twist the relay board, cover off, and it will work again. Seems to be a connection I may have missed. I have reflowed at least 15 connections and added solder to the pin to board connections but apparently haven't hit the right one.

I ordered a relay from Programa but the one I received would blow the #8 fuse. Did 2 in, my original relay did not ever blow the fuse. Sent back and received refund since Programa has no more relays in stock. I too bought a used Klima off eBay, hope it is good.

Has anyone had luck with the aftermarket Kaehler relays available from our host?
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  #9  
Old 09-01-2014, 09:32 PM
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I had an issue earlier this year with the Klima on my 85 300D. Could grab the whole klima and push it fwd and aft and get the compressor to engage and disengage. Found the tabs that go from the pins to the circuit card was lifting the solder traces. Reflow would not work, so used a jumper wire from the tab to a trace destination on the board, all works like a champ; nice cool 62 degree air in the 97 degree florida heat. Certainly no cold, but actually comfortable once all stabilizes.
Mike
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  #10  
Old 09-16-2014, 06:22 PM
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My AC is fixed. I bought a good used klima relay and it did not help. Not long after I started the thread I noticed erratic tach behavior where it would work intermittently. Most of the time the tach would read zero, but if I rev the engine sometimes it would register but only go up to 1000 rpm and not more. If I jumper pins 5 and 7 on the klima relay, I can get the compressor to kick on and then the tach would work normally (register the correct rpm). Knowing that the RPM signal has no connection to the klima relay on the 85 300D, this got me really baffled. The only place the RPM sensor goes to is the EGR computer at the passenger side kick panel. When I was in there a while ago, I had the EGR computer apart (to learn more about how the tach works), I brought out pin 25 EGR amplified tach output signal (with a wire) so I can measure the voltage w/o disassembling the EGR computer. This was documented in this thread Quick Fix: 1985 w123 Tach & A/C after EGR Failure

Anyway, with a DVM on the tach signal wire from pin 25 I saw 1/2 volt AC, if I jumper pins 5 and 7 of the klima to kick in the AC compressor, the voltage goes up to 2 volts AC. This makes no sense to me.

So I pulled the EGR computer off the mount and as I lifted the connector off the socket, a lot of water gushed out! There was much corrosion around the pins and no doubt it was shorting out some of the signals. I scraped all the pins clean and blew dry with compressed air and everything is back to normal. AC and tach works normal again.

Where is the water coming from? It must be coming from the harness! There is a main (fat) cloth tape wrapped bundle (which did not feel wet) and there is a skinny bundle that has a sheath (for the RPM sensor wires) that I think is where the water is coming in from. There is a disconnect for the RPM sensor by the middle of the firewall where I can see the sheath is open and that maybe where the water is entering. I will goop that opening up with Silicone and see if that stops the water. The internals of the EGR computer was totally dry, good it was designed hermetically sealed.

I still am not sure why the tach signal affect the AC compressor. It may have something to do with the OVP relay.

In the diagram below, does anyone know where the OVP relay external pin 1 goes? The diagram says "C circuit 30" but that tells me nothing. There is a circuit 30 withing the relay but where does that wire actually go to? Does it go to the AC compressor clutch? I wish there is one wiring diagram that shows everything.

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Last edited by funola; 09-16-2014 at 07:20 PM.
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  #11  
Old 09-17-2014, 03:51 PM
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Can't help, but thanks for this detailed post since I have the KLIMA box in my 85 CA 300D (AC currently works). While it turned out the KLIMA itself wasn't your issue (only its dependance on rpm signal), it seems that your jumper in post #7 might be a simple solution if one doesn't mind falling back to the 1984- AC control method.

However, I have one question. How does jumpering pins 5 to 10 in the KLIMA socket allow the AC clutch? The schematic in post #5 shows the AC clutch going to pin 7 (and other side gnd), so if pin 7 is open how could the clutch engage? After inserting the jumper, do you also plug the KLIMA box in (piggy-backing over the jumper)?
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  #12  
Old 09-17-2014, 07:13 PM
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Quote:
Originally Posted by BillGrissom View Post
Can't help, but thanks for this detailed post since I have the KLIMA box in my 85 CA 300D (AC currently works). While it turned out the KLIMA itself wasn't your issue (only its dependance on rpm signal), it seems that your jumper in post #7 might be a simple solution if one doesn't mind falling back to the 1984- AC control method.

However, I have one question. How does jumpering pins 5 to 10 in the KLIMA socket allow the AC clutch? The schematic in post #5 shows the AC clutch going to pin 7 (and other side gnd), so if pin 7 is open how could the clutch engage? After inserting the jumper, do you also plug the KLIMA box in (piggy-backing over the jumper)?
I did not jump pins 5 to 10. Doktor Bert suggested jumping pins 5 to 7 to test if compressor clutch is good/ng, doing so will test the clutch but it will still be engaged with key off. In my pic. I actually jumped pins 7 to 10, which allows control of the clutch via the PBU and also clutch will disengage with key off.

There are many old posts on the forum that says the 85 300D Klima relay is also controlled by the RPM sensor. From my research so far, I have found that to be not true.
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  #13  
Old 09-17-2014, 10:34 PM
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Thanks for the clarification. Looking closer, I do see pin numbers 7 & 10 in your photo of post #7. The schematic in post #5 suggests the pressure switch & "temperature control unit (push-button or TempReglar box?) are on the logic side (coil) of the AC clutch relay (inside KLIMA). If so, one must be concerned about putting them directly in series with the AC clutch current, which your jumper does (i.e. might damage them).

However, the schematic for my 1984 (no KLIMA box) has the pressure switch in series with the clutch, but the "temperature control" is on the logic side (simple Bosch relay). Thus, the pressure switch can handle the clutch current, but the temp control box might be damaged by the jumper. I always wondered why they didn't put the pressure switch on the logic side. Perhaps thought safer if directly in series, so a failed relay (fused contacts) wouldn't keep the compressor on and over-pressurize, though it appears to be on the logic side in 1985 cars.
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  #14  
Old 09-18-2014, 12:31 PM
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The compressor clutch draws 3A, the PBU push button switches should handle that no problem (I believe the PBU switches the blower motor directly - the blower draws 16A). I don't think the temp control dial is in the circuit. IMO, even if it were, it should handle 3A (from having it apart and looking at the trace and the switch).

The jumper has since been removed and the AC, Klima and tach is back to factory working as it should.
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  #15  
Old 11-06-2014, 12:21 PM
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I am updating this thread before I forget the details. It's been more than 2 months now since the fix and my AC and tach is still working fine. What knocked out both the tach and AC was water in the EGR computer connector housing. The ensuing corrosion shorted out some of the signals and caused intermittent operation of both the tach and AC. After cleaning off the corrosion, all reverted back to normal. (I take back what I said earlier that the RPM signal is not needed for AC operation. While the RPM signal does not go to the Klima, it is indeed needed by the EGR computer, which indirectly enables the Klima relay).

After cleaning off the corrosion in the EGR connector housing, the AC and tach works again. To prevent this from happening again, I had to stop the water. My windshield is not leaking nor is it leaking from under the battery tray- there is no rust there. What I did was cleaned the area real well and applied RTV on the wire bundle sheathing openings in the engine compartment for the EGR computer and rear RPM sensor (by flywheel), also the grommet on the firewall. There has been many rainfalls since the fix and there is no more water entry into the EGR connector housing and the AC and tach continues to work.

I bought an extra Klima relay in the trouble shooting process. It was not the problem so I have a good Klima for sale. PM me if you need one.
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