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NoSpeedLimits
08-11-2004, 12:10 PM
Instead of bumping up the previous lengthy thread http://www.bimmer.info/forum/showthread.php?p=32840 regarding my A/C problems, I figure I would give it a fresh thread. But, before I begin with the A/C update, I want to let you know that I got my car back and she is looking sweet with the new paint job! I'll post some pics when I get a chance, and access to a digital camera.

Okay, as per your recommendation, I picked up one of those pressure gauges at wally-mart. I hooked her up to the smaller fitting (the one closer to the front of the car). This line connects to the larger diameter tube, which I cannot at this moment recall if that is the high or low pressure side. Just so you know, before I hooked up the gauge, I made a short trip with the car (about 2 miles max) and parked it for about five minutes -- I warmed her up but I didn't run the A/C system. And, without the car running, the pressure (I believe it would be the static pressure) reading was a tad under 100 psi (about 98 psi). So, what does this number tell me? I am not sure, but too me it appears that the system has pressure, but is it enough? If it is enough, should I try jumping the LP switch to see if the clutch will engage?

As always, thanks for help and time!

winfred
08-11-2004, 01:05 PM
anything over about 35 psi and the lp switch will be tripped, if the ac is not turning on i would be looking at fuses and seeing if theres any power in the circuit, there should be power to the lp switch. i've had the main control box under the dash fail and kill off all three functions of the ac switch

NoSpeedLimits
08-11-2004, 01:38 PM
Other than missing fuse #8, all of the fuses appear to be okay. I can attempt to check for power at the LP switch. Before I make this attempt (I hate to ask but better safe than sorry) since I am just not that familiar with A/C systems, could someone please correct me if I am wrong, the LP switch is located on top off the drier (I think that is it's name) located under the air intake box at the right front of the engine compartment???

Otherwise, what three functions of the A/C switch would you be referring too?? Do you mean On, Off, and I am not sure what the third would be???

Also, is there any other symptoms that should I be searching for that would confirm that I have problems with the main control box???

FYI. The indicator light comes on when I turn on the A/C and all the different speeds of the blower motor function properly....there is just no cold air. And everything else in the dash appears to be functioning properly.

Tiger
08-11-2004, 01:51 PM
So with A/C off... you got 100 PSI... that means you do have freon in the system... and your system is holding pressure. When you turn on your A/C... is green light lit? You also must turn on the recirculator just so you don't bring outside air in.

So what happens when A/C is on? The low side has bigger pipe than the high side... and low side will feel cold whereas high side feels warm or hot.

NoSpeedLimits
08-11-2004, 02:03 PM
Yep, green light is lit. The A/C just blows hot air...one day it was working, then the next it wasn't. However, I am not surprised that the A/C is not blowing cold air due to the fact that the clutch is not engaging on the compressor. Based on TimGin's post, it sounds like my lp or hp switch might be malfunctioning. Since I have pressure, I think I may attempt to jumper the lp switch to see if the clutch will engage. I just need help with figuring out which wires to jump.

I guess my confusion with the low and high side was due to the fittings being different sizes, the smaller fitting lead to the larger diameter tube. So, based on your statement, is it safe to assume that I was testing the LP side of the system?? Oh-yah, since the A/C is not working, I never thought to feel for temperature difference in the tubes.

Mr Project
08-11-2004, 03:25 PM
Well, since it's not working you won't feel a temp difference. And yes, the larger-diameter tube (with the smaller-diameter fitting) is the low pressure side.

On my '91 535i, the low pressure switch is a black connector off of the switch, which is mounted to the Receiver/Dryer. I disconnected it and jumpered the vehicle side of the harness.

AllanS
08-11-2004, 03:45 PM
Does the green light being lit imply pressure, or does it just mean that the button's been pressed?

I've been having a similar problem as NoSpeed so I'm following along here.

winfred
08-11-2004, 05:11 PM
rear window defroster
ac compresser
recycle


Otherwise, what three functions of the A/C switch would you be referring too?? Do you mean On, Off, and I am not sure what the third would be

Mr Project
08-11-2004, 06:00 PM
Does the green light being lit imply pressure, or does it just mean that the button's been pressed?

Fairly sure on my '91 that the green light comes on with button press regardless. At least that is what I recall from my recent work. I hit the button with no refrigerant in the system and the light came on even though the compressor was (obviously) not engaged.

sbcncsu
08-11-2004, 06:05 PM
Does the 94 540i have the automatic dual climate control? If so, you may have a problem with the module or the RELAY... I no longer have my Bentley but will research the ETK and TIS.

It is definitely electrical, now to trace it out. Anybody have the bentley with the wiring diagram of the A/C on the 94 540? Can anyone shed some light?

632 Regal
08-11-2004, 08:45 PM
something stupid that I must mention here, if the blower switch is all the way to zero or counter clockwise the AC wont turn on. Sorry if this is a real lame comment but when I bought my car I got additional off cause the air didnt work...thanks to my son we fixed that problem on the way home.

Check yout switches for power at the drier and whatever, one side should definetly have 12 volts when the system is supposidly on, of the other doesnt thats the switch you need to replace.

NoSpeedLimits
08-12-2004, 06:56 AM
Nothing is too stupid...we all have had those momentary oversights that remind us that we are only humans. :) On this particular item, I fortunately did not, and I can confidently say that the blower functions as it should in all positions of the dial.

I could be mistaken, but IMO I feel that the green light would come on regardless if the compressor is functional, I speculate that the light only indicates power at the switch.

Winfred, since in my case the green light comes on, is it safe to assume that the main control box is okay? Since I never use them, is it easy verify that the rear window defroster and recycle operate properly?

Mr. Project, I am a little confused as to what you mean by "vehicle side of the harness." So, to bear on the side of caution, I will attempt to run out to my car and take a digital of what I believe is the lp switch and hopefully you or someone else can point out which wires to jump. In-the-mean-time, feel free to clarify it with your words and hopefully you'll save me the trouble of stepping out to take a photo -- I would be greatful since everybody in the office has a view of the parking lot and I will therefore be hammered by curious/nosey co-workers. ;)

BTW - anyone know where the hp switch located?

sbcncsu
08-12-2004, 07:20 AM
I was reading the TIS last night and noticed that the later model BMWs use combination switch that is a Low, Medium, High pressure switch all in one. Again, I don't have a bentley any longer but the wiring should be in that book. It will tell you which wires in the connector are the low, medium and high.

The combination switch is mounted on top of the accumulator (receiver drier) and has one connector with 3 or 4 wires.

Mr Project
08-12-2004, 07:38 AM
The combination switch is mounted on top of the accumulator (receiver drier) and has one connector with 3 or 4 wires.

NSL, in my case I do have the single 'combo' switch on the Receiver/Dryer, but rather than 1 large connector coming from it, I have 2 small ones. Each connector on mine is 2 wires. One connector is grey, one connector is black.

By "Vehicle Side" I simply mean that when you disconnect the connectors so that you can put a jumper in, it won't do any good to jumper the side (wires) that goes to the switch. In order to 'fool' the DME (or whatever runs this) into activating the compressor clutch, you have to jumper the connector that goes back into the vehicle. Obvious, but I figured as you said "nothing is too stupid". :)

On my car, jumpering the grey connector activated the compressor clutch. (A/C button was "ON" in the car, probably required) Jumpering the black connector just activated the aux. fan. (probably the high-pressure switch)

I'm not sure on mine how it would determine the 'mid' level pressure by using those 2 connections. Maybe a certain combination of the 2 signals?

NoSpeedLimits
08-12-2004, 09:18 AM
I pulled this image from the electronic parts catalog...based on your description, I believe the lower drier shown in the picture matches what is in our vehicle. Thanks IOU for taking the time to explain it...you saved me a bunch of unsolicited socializing. ;)

Mr Project
08-12-2004, 10:07 AM
Exactly. That #2 style is what I have in my '91, and presumably what you would have in your '94.

NoSpeedLimits
08-12-2004, 11:47 AM
Okay...the verdict is in, I jumped both of the connection and the first one fired up my auxiliary fan. The second lead...drum roll please...fired up the compressor and gave me cold air. Yippy! :) So, I believe it is safe to assume that my lp switch needs replacement???

If my assumption is true...is it safe for me to unscrew the lp switch and replace it myself??? I am concerned about the system being under pressure and possibly causing me harm. Also, will the removal of the lp switch cause refrigerant to leak out??? Any recommendation would be appreciated. I'll check my Bentley after work today to see if they have any information pertaining to this procedure.

Mr Project
08-12-2004, 11:49 AM
I wondered about this myself... on my Receiver/Dryer, the port for the combo switch has a schraeder valve, so it can be changed without releasing a significant amount of refigerant.

NoSpeedLimits
08-12-2004, 12:14 PM
Thanks to BMA...I will have the replacement pressure switch tomorrow. And, if all goes well with DIY job then I should be enjoying A/C this weekend :)

FYI. The pressure switch p/n = 64 53 1 390 070 (BMA p/n = BM044273) and costs less then forty bucks.

Thanks for all of your help!

TimGinCentralNJ
08-12-2004, 02:02 PM
something stupid that I must mention here, if the blower switch is all the way to zero or counter clockwise the AC wont turn on. Sorry if this is a real lame comment but when I bought my car I got additional off cause the air didnt work...thanks to my son we fixed that problem on the way home.

Check yout switches for power at the drier and whatever, one side should definetly have 12 volts when the system is supposidly on, of the other doesnt thats the switch you need to replace.

632 Regal
08-12-2004, 06:30 PM
Thanks to BMA...I will have the replacement pressure switch tomorrow. And, if all goes well with DIY job then I should be enjoying A/C this weekend :)

FYI. The pressure switch p/n = 64 53 1 390 070 (BMA p/n = BM044273) and costs less then forty bucks.

Thanks for all of your help!

NoSpeedLimits
08-17-2004, 08:24 AM
Problem fixed, thanks to all those who helped! Installation took about 15 minutes -- piece of cake. The amount of refrigerant lost is dependant on how quickly one can unscrew the switch -- not much leaked out. The wires out of the back of the switch slow the removal and installation process.

I was disappointed to see that my auxiliary fan is still not functioning. Not exactly sure why I was able to get it to operate when I jumped the pressure switch, but with the new switch installed it still does not work. Low speed with the A/C on, not sure about high speed. I'll attempt to jump the temp switch located on the side of the radiator and see if that kick starts the fan. If not, then I plan to replace the resistor. Sound right???

DanDombrowski
08-17-2004, 08:42 AM
Awesome man. This is one for the books. Good thing you got that expensive electrical diagnosis and compressor replacement from the repair shop, right?

gvilkelis
08-17-2004, 08:53 AM
If the aux fan works on low speed when A/C is on, it means that the resistor is OK.
Resistor is used only for aux fan low speed operation.