ac still not working after ac conversion 87 300SDL - Page 6 - PeachParts Mercedes-Benz Forum

saumil · #76 07-03-2007, 12:01 PM

Evaporator, in-car, heater and outside temp sensor send their input to the push button unit, and then the push button unit sends the signal to the Klima unit accordingly.

Brian Carlton · #77 07-03-2007, 12:28 PM

Quote:

Originally Posted by sixto

That's very thorough!

Isn't there an evaporator temp switch between the PBU and the Klima to cut the compressor if the evaporator ices?

Sixto
87 300D

On the early W-126, this is the situation. The evap temp switch is between the PBU and the compressor relay.

The low pressure cutout switch is between the compressor relay and the compressor on the load side.

The SDL's are as described by Saumil.

Smokes alittle · #78 07-07-2007, 05:57 PM

Quote:

Originally Posted by saumil

This has gotten very confusing, lets start again, now that you have a good grip on what is the Klima relay and what is the CCU (I think you mean the push-button unit inside the car).

1. Turn Car Off
2. Pull Klima Relay Out
3. Put your multimeter on DC Volts setting
4. Connect the ground terminal of the meter (black color usually) to the battery's negative terminal
5. Connect the positive terminal of the meter to pin number 5 in the socket (Hopefully, you know which pin is 5)
6. You should get close to 12V, if not, the fuse is blown (#7 I think). Replace fuse. Put the Klima relay back in and check a/c again.
7. If the fuse is o.k. and the compressor clutch still does not run, then lets move on
8. Remove the Klima relay. Now connect the negative terminal of the meter to pin number 10 in the socket. (Hopefully you know which is pin 10). Put the positive terminal of the meter on the positive terminal of the battery.
9. Turn on the car and press one of the a/c switches on the push button unit.
10. You should get close to 12V when the a/c switch is on.
11. If you dont get close to 12V then there are one of two possibilities:
a. the push button unit is not sending the correct control signal
b. the pressure switch is not closed
For now, I am ignoring the trivial possibilities that wires or connectors may be broken. We can dive into these once we have some answers to the basic tests.
12. Turn the car off.
13. If you dont get the 12V, disconnect the two cables from the pressure sensor (should be at the drier), and jumper them.
14. Repeat steps 9 and 10.
15. If you still dont get the 12V, the push-button unit is not sending the signal.
16. Turn car off, dont keep the car running for a long time with the pressure switch cables jumpered.
17. If at step 14, you did get 12V, then the pressure switch is not closed
18. If the pressure switch is not closed there could be three possibilities:
a. refrigerant pressure is too low (lower than 2 bar)
b. refrigerant pressure is too high (higher than 30 bar)
c. the pressure switch is bad
you will need pressure gauges to seperate these possibilities.
16. If at step 11, if you did get 12V, then the push-button unit is sending the control signal and the pressure sensor is o.k. and we will move on.
17. If push-button unit is sending a signal and the pressure sensor is o.k. but the compressor clutch will still not run, then need to check the compressor clutch coil resistance.
18. Connect the positive terminal of the meter to pin number 7 in the socket and negative terminal of the meter to negative terminal of the battery.
19. Change the setting of the meter from volts to ohms.
20. You should get a low resistance about a few ohms.
21. If you don’t get a low resistance, need one last test.
22. Get to the compressor and disconnect the connector for the compressor clutch coil (there is a speed sensor cable that connects to the compressor connector also, you have to trace the clutch wire to the compressor connector to pick the right pin on the connector).
23. Put one of meter’s terminals on battery ground and the other terminal on the compressor’s clutch coil pin (polarity does not matter).
24. You should get a low resistance, about a few ohms. If you do get the low resistance at the compressor then compressor clutch coil is o.k.
25. If you get low resistance in step 23 but do not get a low resistance in steps 18-19, then the cable from the Klima relay to the compressor is bad, replace it.
25. If you don’t get a low resistance in step 23, then the compressor coil is open, normally this would require a new compressor.
26. If the compressor clutch coil is o.k. and the cable from the Klima relay to the compressor is o.k. then let us move on.
27. At this point, if the fuse is o.k., and the compressor coil’s resistance and cable are o.k., then jumper pin number 5 and 7 in the socket.
28. Turn on the car and your compressor should come on.
29. Turn car off
29. If the compressor does not come on, there are two possibilities:
a. the fuse is blown
b. the compressor has an internal mechanical problem, is likely seized.
30. No matter whether it is 29a (shorted coil) or 29b (seized), compressor is bad, replace it.
31. If the compressor comes on at step 28, but does not come on when the Klima relay is put back in and the push button switches are on a/c, then the Klima relay is not producing the 12V signal at its pin 7 to drive the compressor.
32. If Klima relay is not driving the compressor at step 31, then there are five possibilities:
a. the temperature sensor is bad
b. faulty throttle cutout microswitch
c. bad compressor speed sensor
d. bad engine speed sensor
e. bad Klima relay
33. Put the meter back on voltmeter setting. Do this test with engine cooler than 105 deg-C, better when just cold.
34. Put the positive terminal of the meter on the positive terminal of the battery. Put the negative terminal of the meter in pin 12 of the socket.
35. If you get about 12V, then the temperature sensor is bad. I am not sure about the physical location of this sensor but on my 87 260E, it is a 3 pin sensor on the engine I think third from last from the windshield side. You can ask your parts vendor about it.
36. If the temperature sensor is bad, then disconnect the sensor cables, put the Klima relay back, and try you’re a/c. If this was the only bad component, your compressor should start working. But again, don’t keep running like this, replace the sensor as soon as you can. If disconnecting the temp sensor cable does not work, there is still another problem. Remove the Klima relay and move on.
37. Put the positive terminal of the meter on the positive terminal of the battery. Put the negative terminal of the meter in pin 4 of the socket.
38. If you get about 12V, then the throttle cut-off switch is bad. This switch is supposed to be open and only close when the throttle is wide open. I am not sure about the physical location of this switch but you can ask your parts vendor about it. Once again, if you can find this part, you can disconnect the wire, put the Klima relay back and check a/c. If it still does not come on, then there is some other problem and move on.
39. Change the meter setting to measure resistance.
40. Put the positive terminal of the meter on pin 9 of the socket. Put the negative terminal of the meter in pin 11 of the socket.
41. You should get about 350 – 450 ohms. If you don’t get the low resistance but get very high resistance, either the compressor speed sensor is open circuit or the wire is broken somewhere. Do the same test as close as possible to the speed sensor (i.e. on the compressor connector) to rule out a broken wire. Replace sensor if it is bad.
41. If the resistance is o.k., then, jumper pins 5 and 7 on the socket.
42. Change the meter setting to ac volts.
43. Turn on the car.
42. You should get about 0.3V ac at idle of about 750 rpm. If you don’t get the ac voltage, and the resistance was kind of o.k., replace the sensor.
43. Turn off the car.
43. To check engine speed signal, put the meter setting to ac volts
44. Connect one terminal of the meter to pin 1 of the socket and the other to pin 2 of the socket.
45. Turn the car on.
46. At idle of about 750 rpm, you should get a voltage greater than about 4V ac. And the voltage should increase with increase in RPM.
47. Stop the car
48. If you don’t get the voltage, switch the meter to resistance setting and readout the resistance between pins 1 and 2 of the socket.
49. You should get about 2 Kohms. If you get a very high resistance, check the resistance closer to the sensor to rule out a cut in the cable. Otherwise replace the sensor. Ask the parts person about its location.
50. If in step 15, you determine that the push-button unit is not sending the control signal, replace the push-button unit. This has happened to me once, the electronics driver inside the push-button unit is blown and it will not send the control signal to the Klima relay. What I did is bypassed the electronics and just used the mechanical switches to send the control signals. The downside is that there is no more auto modes, so when I feel like it is too cold, I would press the economy switch and I designated that switch to send a signal to cut-off the compressor. So my brain does what the box would otherwise do, have still not fixed the electronics, just a big headache to test this unit once it is out of the car. If you just bought a new one, you can ask for a replacement. Most likely the problem you are having is not in that unit.

This is awfully long and I may have missed some possibility, but you will have enough info to test this problem in a systematic manner and when you come to a point where you think something is missing, let us know, some one will help.

Saumil and Brian, Thanks to both of you. You guys do a great job of dumbing it down. My son and I have been trouble shooting on my 86 SDL and here is what we've found concerning the test you've decribed above :

#5 No voltage / fuse was good

#8 No voltage

#13 and 14 Got 12 volts

From this point we tested with low pressure switch jumped

#18 We measured 3.4 ohms

#22 and 23 We measured 0 ohms.

I suspect that my wire from KLIMA relay to the compressor clutch (looks like it is green/blue) is bad because, When we connected a wire from the postive post on the battery directly to the inside terminal on the compressor (with it unplugged) the clutch would engage. I hope I haven't confused you guys more. Are we going in the right direction ?

saumil · #79 07-07-2007, 09:19 PM

O.K., so far you have valuable information.

No voltage on pin 5, in step 5 is a big problem if the fuse is o.k. Because this means you are not getting any power to the Klima relay. The cable from the fusebox to the Klima socket is bad. Or you may not have looked at the correct pin, so I am attaching the pin diagram, please double check.

The pressure switch also was not closing, so either the switch is bad OR you are low on refrigerant. For this you have to hook up a pressure gauge and check, but for the purpose of performing the rest of the tests, shorting the pressure switch is o.k. Because you get the voltage on pin 10 after shorting, your pushbutton signal is o.k.

The low resistance in step 18 tells us that the compressor clutch coil is not open and it also tells us that the wiring from the Klima relay to the compressor is o.k., contrary to what you concluded. The tests in #22 and #23 were not required if step 18 yielded low resistance. But you anyway confirmed that the clutch is engaging with direct 12V, so it is safe to assume that compressor will engage if the Klima relay problem is fixed.

I think you guys are doing quite well and are on the right track. But before you go any further, find out why there is no voltage in step 5. Without this voltage, the relay will just not work.

Good-luck.

Smokes alittle · #80 07-08-2007, 09:35 AM

Thanks, We will check the problem of no voltage at #5 pin and report back.

saumil · #81 07-08-2007, 11:44 AM

There is one other possibility, the Klima relay you have is different from the one in my 87, 260E. With the car off, check every pin on the relay socket to see if there is 12V anywhere between the pin and the battery ground. There should atleast be one pin on the relay socket that should have 12V. If this is not the case, then for sure there is a big problem and I would assume that the voltage pin is pin 5 and do further test.

Car is off in these tests

1. Remove fuse # 7
2. Put meter in volts mode. One terminal (black) of the meter on battery ground
3. Second terminal of meter on one end of the fuse socket, try both socket pins.
4. You should get 12V on one socket pin and nothing on the other.
5. If you dont get 12V on any of the fuse socket's pins, then the wire from the battery to the fusebox is broken somewhere.
6. If you do get 12V on one of the pins, then the next test is to check the wire from the fusebox to the Klima relay
7. Put meter in ohms mode. Put one end of the meter on the fuse pin that did not get the voltage.
8. Put other end of meter on pin #5 in Klima socket.
9. You should get 0 ohms. If you dont, then the wire from the fusebox to the Klima socket is broken. Infact, you can put the other end in all the pins to fish around if the fuse wire ends up at any other location in the Klima socket.

Good-luck

Brian Carlton · #82 07-08-2007, 11:54 AM

Quote:

Originally Posted by saumil

There is one other possibility, the Klima relay you have is different from the one in my 87, 260E. With the car off, check every pin on the relay socket to see if there is 12V anywhere between the pin and the battery ground.

Saumil, he's got the '87 SDL with the identical pin configuration as you originally posted. He must have voltage on socket #5 or we can't go further.

saumil · #83 07-08-2007, 10:57 PM

I was checking the wiring diagrams, and it seems that for 87, diesel, pin 5 on the Klima socket will have 12V all the time BUT on 87, Gasoline, pin 5 has 12V only in run or start mode. So please check pin 5 again, this time with car on. Maybe even though your car is diesel, it may only send voltage to pin 5 when the car is on.

Brian Carlton · #84 07-08-2007, 11:26 PM

Quote:

Originally Posted by saumil

I was checking the wiring diagrams, and it seems that for 87, diesel, pin 5 on the Klima socket will have 12V all the time BUT on 87, Gasoline, pin 5 has 12V only in run or start mode. So please check pin 5 again, this time with car on. Maybe even though your car is diesel, it may only send voltage to pin 5 when the car is on.

We should probably refer to the "pins" as "sockets" to prevent confusion..........we don't want a check of the pins on the Klima..........now sitting outside the vehicle.............

saumil · #85 07-09-2007, 12:11 AM

Yes, Brian is perfectly correct, pins generally refer to a male type terminal, how about socket terminals ? Please check Klima socket terminal 5, with the car running this time, to make sure that the 12V is still absent.

Smokes alittle · #86 07-10-2007, 10:04 PM

Sorry guys haven't been able to get back to it yet. But I have your suggestions and will try soon maybe Wednesday night. Thanks.

aquaman0001 · #87 07-11-2007, 03:03 PM

I have noticed with my push button set to off. My defrost will come on by itself, blowing hot air(probably from engine compartment). I have no voltage on #5 and fuse LOOKS good.(did not test). Any thoughts on why the defrost is coming on by itself.
A

saumil · #88 07-11-2007, 03:29 PM

The automatic starting of blower motor and/or the opening of the monovalve appear to be a problem with your push-button unit sending an inappropriate signal, most likely a bad push button unit itself. But the problem of blower starting automatically is unrelated to the Klima relay and its control. Blower motor and monovalve for heat are controlled solely by the push-button unit. Klima relay is incharge of operating (more like cutting off in case of any problem because it sits on the same belt) the compressor.

You said, you dont have a voltage on Klima socket terminal 5 even when the car is on, then the Klima relay cannot operate and hence the a/c compressor can never be turned on. The fact that your blower motor is working (even if it is unwanted) tells us that there must be voltage on the fuse, so then the wire from the fuse to the Klima relay's socket terminal 5 is disconnected somewhere.

sixto · #89 07-11-2007, 07:24 PM

Is the blower motor running when defrost engages on its own? If not, maybe having no power to the CCU sets the defrost flaps and monovalve to open (default position) and you feel warm air only when the car's moving.

Sixto
87 300D

p.s., you haven't answered my fuel line question

saumil · #90 07-11-2007, 11:30 PM

Yes, sixto has an excellent point. I assumed that the blower motor is running BUT what if the situation is exactly as sixto described, very much possible. You need to check voltage on the fuse # 7 (any of the two ends of the fuse) first. If there is no voltage there, then the wire from the battery (for diesel) or the ignition switch (for gasoline) to the fuse is broken somewhere. If there is voltage on both sides of the fuse then the wire from fuse to Klima socket terminal 5 is broken somewhere.