Compressor speed sensor.
It appears that my a/c system has a bad compressor speed sensor. I'd really rather not replace it, as I'd have to empty the system at the very least. And I may not be able to get access without removing the compressor. So rather than replace the sensor, I'm wondering if there's some workaround for the Klima. Admittedly, a bad belt would be a major issue without the Klima function, but that's a risk I may be willing to take.
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Straight Wire the Comp Clutch to a Switch
In the Passenger compartment.
Suicidal for the Mercedes BUT At Least before it overheats (Or Worse) the Captain will be Cool. |
x2 ice cube relay in place of Klima relay. You also lose compressor cutoff from the 105/125 switch or whatever version you have but who drives a 601/2/3 without one eye on the temp gauge?
Sixto 83 300SD can be yours 98 E320s sedan and wagon |
I suspect a seized compressor would shred the belt before it shredded the engine.
A simple switch doesn't cut it. I'd have to patch it in through the ACC system so that the compressor comes on and off with system demands. I'm going to try to scope it tomorrow. If there's still a low signal, maybe I can add a simple amplifier. |
BTDT -
http://www.peachparts.com/shopforum/diesel-discussion/230504-klima-relay-deleted-om603.html http://www.peachparts.com/shopforum/diesel-discussion/326800-klima-bypass-question.html Sixto 83 300SD can be yours 98 E320s sedan and wagon |
I can modify a Kilma which only monitors the freon. It will by-pass everything. You will have the full function of the ACC buttons. PM me if you are interested.
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Ah...no. I can do the same thing, but there are functions performed by the Klima that I think are important, like: 1) controlling the kickdown solenoid 2) Turning off the compressor when coolant temp is over 105 3) Turning off the compressor at full throttle. I can probably make all of this happen with two or three relays. Or maybe I could come up with a circuit mod for the Klima board. Or if the sensor has a bit of output, boost it with a single stage amplifier. Or just throw in the towel and replace the sensor. |
How about faking the compressor signal?
Sixto 83 300SD can be yours 98 E320s sedan and wagon |
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This is about the simplest possible wiring plan if I wanted to replace the Klima with dumb relays and not screw something else up. Explanation:
- Pins 4 and 12 are the full throttle and high temp cutout signals. They present ground when either condition is satisfied. These pins get wired to a standard DIN relay, which is set up as NC. Pin 5 on the Klima is the power source for the whole system. Unless a problem is signaled, this relay will present 12v+ on 87a. This will be used to power the coil of the other relay. - The diode is required to prevent the fan from coming on high speed when the throttle is floored. - Pins 5&6 are kickdown control, they are simply bridged. - Pin 10 presents ground when the CC head unit wants the compressor on. This controls the coil on the compressor relay. - Pin 7 is the compressor clutch. To sum up: the cutout relay will shut down the compressor relay if the accelerator is floored or if the high temp switch closes. Otherwise, the compressor relay is controlled by the pressure switch and the CC head unit. Disadvantages: - not sure if there are situations where the Klima shuts off the kickdown solenoid. The jumper bypasses control entirely. - No 'belt protection' from the compressor sensor, but that was the goal so it's good/bad. - Looking at it, I'm pretty bummed by how non-obvious it is. Anyone stumbling into it would really have a head scratcher. It took me a while to put it together, and it would take longer for someone reverse engineer. But I must admit, having spent twenty or thirty years reverse engineering Bosch cr_p, it's almost sweet revenge. Just for the permanent record, the pinouts on the Klima are as follows: 1 Ground 2 Engine RPM 3 Not used 4 Accelerator microswitch (normally open/grounds at full throttle) 5 12V+ from fuse box, hot in run 6 Kickdown switch/solenoid 7 AC compressor 8 Not used 9 AC RPM Sensor (red) 10 Pressure switch (normally grounded) 11 AC RPM Sensor (white) 12 High temperature switch (normally open/grounded when too hot) |
There is one other function that the Klima relay performs that is not taken care of by the solution above: There is a delay engaging the compressor clutch until the engine is running at an RPM above crank speed.
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1 Attachment(s)
CORRECTED DIAGRAMS:
1 Ground 2 Engine RPM 3 Not used 4 Accelerator microswitch (normally open/grounds at full throttle) 5 12V+ from fuse box, hot in run 6 Kickdown switch/solenoid 7 AC compressor 8 Not used 9 AC RPM Sensor (red) 10 12V+ from control unit through pressure switch 11 AC RPM Sensor (white) 12 High temperature switch (normally open/grounded when too hot) |
Awesome work, thanks!
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Just take it one step at a time, I still haven't made this work. Pin 10 seems to put out .75V, I can't figure out why.
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