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7 Series - E38 (1995 - 2001)

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  #1  
Old 06-11-2013, 08:33 PM
bimmerhaas bimmerhaas is offline
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another ac compressor question

ive got a 1998 740 the ac has never worked since ive owned it, the freon is full, and as far as i can tell all the fuses and relays are good...i can jump the compressor and it turns on and the system blows cold air...so since i was out of ideas i took it in to have it diagnosed and i was told it was the compressor, according to them even tho i could jump it and it works, it was still bad...does that sound right? or am i missing something?
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  #2  
Old 06-11-2013, 09:48 PM
Mayorchuck Mayorchuck is offline
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Is the ambient (outside) temp on your cluster correct? If it shows -40, your sensor is bad and the a/c won't turn on. The temp sensor for the coolant must be below 120. Any issues with either of those you are aware of? Sounds more electrical to me if you can jump it and get cold air, that is if the freon is fully charged.
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  #3  
Old 06-11-2013, 10:06 PM
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ebida3 ebida3 is offline
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If the compressor spins, the compressor is good. The compressor is just a pump. Sounds like a sensor or relay like Mayorchuck said.
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  #4  
Old 06-12-2013, 04:21 PM
zachiepie zachiepie is offline
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I have the same problem and can't figure it out. My Check Coolant level warning comes on, could that be a part of it? BTW I don't have to add very much coolant to make the plunger pop up, maybe 200 mLs or so. Must be a sensor.
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Last edited by zachiepie; 06-12-2013 at 04:21 PM. Reason: Hit "enter" before I was actually finished.
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  #5  
Old 06-12-2013, 04:39 PM
Mayorchuck Mayorchuck is offline
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Could be the level sensor on the expansion tank. Have you done any work lately, i.e. water pump, hoses? Air in the system can cause this and also temp spikes on the needle. If not, I would remove the plug to the sensor and see if there is any dried (white) coolant. If so, best to replace the tank and sensor. Even if not the sensor could just be bad. I think you can get to it by just removing the air filter box.

Here is a link from Timm's site that has a good pic of the sensor and also shows how to remove the tank if needed.

http://www.meeknet.co.uk/e38/Alterna...eplacement.htm
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  #6  
Old 06-12-2013, 06:31 PM
bimmerhaas bimmerhaas is offline
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Re: another ac compressor question

I have changed the sender expansion tank but I've reused the sensor as well as I've changed the heater hoses of of the heater control valve as well as the valve itself....as far as the temperature I don't know what the coolant temp is the gauge on the dash is in the 12 o'clock position when up to temp so I'm guessing its ok

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  #7  
Old 06-12-2013, 08:42 PM
zachiepie zachiepie is offline
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Quote:
Originally Posted by Mayorchuck View Post
Could be the level sensor on the expansion tank. Have you done any work lately, i.e. water pump, hoses? Air in the system can cause this and also temp spikes on the needle. If not, I would remove the plug to the sensor and see if there is any dried (white) coolant. If so, best to replace the tank and sensor. Even if not the sensor could just be bad. I think you can get to it by just removing the air filter box.

Here is a link from Timm's site that has a good pic of the sensor and also shows how to remove the tank if needed.

http://www.meeknet.co.uk/e38/Alterna...eplacement.htm


Would this cause the ac compressor to not turn on? I mean, the snowflake button is lit, but the compressor isn't spinning.
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  #8  
Old 06-12-2013, 09:26 PM
Mayorchuck Mayorchuck is offline
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I don't believe the level sensor has anything to do with the compressor. This car is picky about things but I don't think that is one of them. Try unplugging the wire to the compressor clutch to see if you have 12v when the button is pushed. Most common problems is the system not being fully charged. Have you had the low/high pressure checked? Too high or too low and the clutch will not engage. That and the few things mentioned earlier in the thread are things I would check if it were mine.
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  #9  
Old 06-12-2013, 11:33 PM
zachiepie zachiepie is offline
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Quote:
Originally Posted by Mayorchuck View Post
I don't believe the level sensor has anything to do with the compressor. This car is picky about things but I don't think that is one of them. Try unplugging the wire to the compressor clutch to see if you have 12v when the button is pushed. Most common problems is the system not being fully charged. Have you had the low/high pressure checked? Too high or too low and the clutch will not engage. That and the few things mentioned earlier in the thread are things I would check if it were mine.

The levels are good, actually. That was one of my first assumptions. When I check the compressor terminals, it is NOT getting 12v with the switch on, but I don't know what would innervate that. I can certainly jump it with a 12v wire, anyways. Do you know of any schematic out there? I can't seem to find one.

And I apologize to the OP, but I think this might help him out as well
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  #10  
Old 06-13-2013, 12:07 AM
Mayorchuck Mayorchuck is offline
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http://www.bmw-planet.com/diagrams/r...8new/index.htm

NOTE: Check fuse 11. I noticed while working on my system a few days ago that it protects the compressor.

I will warn you to watch for anything DDE/Deisel/M51 when looking at compressor info. I like using the search box at the bottom left of the page. I have recently started doing a study on the blower motor as there seems to be a number of issues come up as it gets warm each year. Here is the link to the info I have posted so far on another forum. I have not screen printed any of the schematics as of yet but the pin out into might help. I think info on your car will be the last that I posted.

http://forums.bimmerforums.com/forum....php?t=2003822
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  #11  
Old 06-13-2013, 01:04 PM
sas_man sas_man is offline
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Your speedometer may be a part of the issue

Hi:

I had my speedometer and MID out for pixel repair. During this time I had my AC recharged at my son's shop. When we went to test the air conditioner, the compressor would not turn on. We could jump it and the compressor would run.

I had just taken the IKHA apart to lub the intake fan (the low buzzing noise that sometimes comes from the fan controls when you turn off the car) and thought I screwed it up.

The speedometer and MID came back from BimmerOnly yesterday. When I installed the speedometer and MID back in the dash, the AC started working again. So I agree that the outside air temp sensor might have something to do with it.
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  #12  
Old 06-13-2013, 09:55 PM
Mayorchuck Mayorchuck is offline
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Quote:
Originally Posted by sas_man View Post
Hi:

I had my speedometer and MID out for pixel repair. During this time I had my AC recharged at my son's shop. When we went to test the air conditioner, the compressor would not turn on. We could jump it and the compressor would run.

I had just taken the IKHA apart to lub the intake fan (the low buzzing noise that sometimes comes from the fan controls when you turn off the car) and thought I screwed it up.

The speedometer and MID came back from BimmerOnly yesterday. When I installed the speedometer and MID back in the dash, the AC started working again. So I agree that the outside air temp sensor might have something to do with it.
Good info. The outside temp sensor does feed directly to the IKE (cluster). The IKE puts that info on the I-Bus/K-Bus. So the DME gets the information from the cluster, not the sensor itself. So if the cluster is removed, there is no loop to the DME. The DME would read that as the default temp of -40F. The DME will not send power to the clutch in that case.
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  #13  
Old 06-14-2013, 11:13 AM
bimmerhaas bimmerhaas is offline
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Re: another ac compressor question

OK dumb question time I've found the pressure switch under the air filter is there another pressure switch meaning is there 2 switches?....if so where and which is which....I've tried replacing the one under the air filter with another one but still had no luck

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  #14  
Old 06-15-2013, 01:57 AM
zachiepie zachiepie is offline
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Quote:
Originally Posted by bimmerhaas View Post
OK dumb question time I've found the pressure switch under the air filter is there another pressure switch meaning is there 2 switches?....if so where and which is which....I've tried replacing the one under the air filter with another one but still had no luck

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Sure is a complicated car. I've suspected the high side switch as my problem as well, and I don't see any others from the schematics I've seen. I'm surprised replacing that switch didn't fix it
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  #15  
Old 06-15-2013, 01:59 AM
zachiepie zachiepie is offline
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Quote:
Originally Posted by sas_man View Post
Hi:

I had my speedometer and MID out for pixel repair. During this time I had my AC recharged at my son's shop. When we went to test the air conditioner, the compressor would not turn on. We could jump it and the compressor would run.

I had just taken the IKHA apart to lub the intake fan (the low buzzing noise that sometimes comes from the fan controls when you turn off the car) and thought I screwed it up.

The speedometer and MID came back from BimmerOnly yesterday. When I installed the speedometer and MID back in the dash, the AC started working again. So I agree that the outside air temp sensor might have something to do with it.

I've never taken my dash out, and I can't think of any sort of random repair project like that I may have done since my compressor problems. My outside air temp works fine, so the DME should be reading that end correctly. Good info though.
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  #16  
Old 06-15-2013, 08:42 AM
Mayorchuck Mayorchuck is offline
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Going to have to dig deeper. If the pressure and said sensor are good, there is an evap sensor that is listed as a cutoff:



You may need to pull your control panel out and to see if the snowflake is sending a signal. Pin outs are in the link in my post above.

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  #17  
Old 06-15-2013, 06:24 PM
zachiepie zachiepie is offline
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Mayorchuck you rock. Thank you for the help.

After digging through it all, it almost seems as if my AC control panel is going bad. The snowflake light is on (it wasn't a few weeks ago) and I can't get the Max AC light to turn on. Not sure if it's supposed to be off if the compressor is off, but that's what I'm leaning towards anyways.

Man, these are complicated.
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  #18  
Old 06-15-2013, 06:47 PM
Mayorchuck Mayorchuck is offline
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Use a meter and push the button on and off. Don't let the LED's make that decision. Mine are sporadic at best. Some days they work, others they flash and sometimes nothing at all. But all the buttons work as they should, even when the LED's are out. If you do get another IHKA, get one the same year or newer. If you have MAX, be sure to get the same and not one that says REST. Would be ideal if you had someone you could swap long enough to test it.
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  #19  
Old 06-17-2013, 06:17 PM
jitsjaf2009 jitsjaf2009 is offline
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The assumption seems to be since jumping it put out cold air there is enough Freon. It may be the low level holding it out. If you haven't got the gages, buy the Freon set up at the auto parts with a gage...set it out in the sun for awhile...hook it up and turn on the a/c. It should allow enough flow into the system to allow the low pressure switch to engage and allow the compressor to kick on. You could jump the clutch and do it that way, but I feel safer doing it with the warmed up can of Freon.
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  #20  
Old 06-22-2013, 01:56 PM
zachiepie zachiepie is offline
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My mechanic and I (he's my brother) are heading out of town, but we'll double check the pressures when we get back. I assume that you guys are saying that the only way to get a truly accurate pressure read is to jump the compressor and hook up our gauges? And yes, we have an actual set of pressure gauges, the ones you plug in high side and low side (not the cheap ones at the parts store).
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